Lumolabs: Sensors of Nikon D700, D5000 and Pentax K-x

(Photo ©2009 Karsten Pawlik.)

After the interesting findings about the relatively good dynamic range properties of the Pentax K-x (cf. Lumolabs: Pentax K-x sensor quality), many have requested to publish a comparison with some other well known camera models.

Well, I am happy to announce that a great photographer and dear friend of mine, Karsten Pawlik (kafenio.org) shares my passion and we could spend some time in studio together in order to compile this comparison.

Most of the photos (e.g., all Nikon photos) presented in this article are © Karsten Pawlik. The opening photo shows two Pentax K-x with the gorgeous Pentax FA 31/1.8 Limited lens, in both black and silver color.

It is interesting to compare the K-x with these two cameras from Nikon for the following reasons:

1. Nikon D5000 and Pentax K-x may share the same Sony Exmor sensor which is supposed to be found in the Sony A500 too. (well, maybe not: DxO measures that the A500 has a different sensor)
2. Nikon D700 is a full frame camera and captures 1.2 stops more light than both the Nikon D5000 and Pentax K-x which are both APS-C only. It is interesting to see if this advantage shows in images.

1. ISO Noise


(please click on the photo above (and all others) for better readable versions)

The above chart summarizes the noise levels for 18% gray patches (2800 °K tungsten) at various values for ISO: 100, 1600 and 12800, measured as a signal to noise ratio (SNR [dB]). Please read Lumolabs: Welcome and testing methodology for details about how we measure these values. Towards the end of this article, you'll find links to all original test shots suitable for further examination.

Within this article, I will ignore the fact that the D5000 delivered the best SNR at ISO 100. AT ISO1600, we see the expected result: About 3dB or 1 f-stop (1EV) advantage for the full frame D700 with respect to both D5000 and K-x.

At ISO 12800, the K-x manages to match the result of the D700 while the D5000 behaves as expected. However, the SNR should decrease by at least 9dB when going from ISO 1600 to 12800 while it only decreases by only about 6dB for the K-x. This is a sign for raw file noise reduction at work for the Pentax and I believe that all SNR values for Pentax K-x should be reduced by 3dB for ISO values of 3200 or higher.

(Note: The D5000 has no native setting of ISO 12800. It was emulated using ISO 6400 and exposing like for ISO 12800, pushing 1 stop in postprocessing.)

In summary, we confirm the 1 stop advantage for the full frame sensor as far as high iso gray level noise is concerned.


2. Dynamic range

The situation turns out to be more complicated when we study the respective dynamic ranges. Let's start with the full SNR curves for all cameras.


Look first at the three red (D700 full frame), blue (D5000) and green (K-x) curves in the middle of the graph: These are the ISO 1600 curves for the three camera models and the red line lying above the others shows the full frame advantage we have been talking about above. The curves show how the signal-to-noise ratio decreases (relative noise increases) towards the shadows (the lower luminosities towards the left). At ISO 1600, the full frame advantage remains significant throughout all luminosities spanning 7 stops (1%). Note that the curves at ISO12800 may be "polluted" by noise reduction tricks for the APS-C sensors.

Most important for the determination of dynamic range are the SNR curves at lowest ISO (i.e., ISO 100). In order to measure deepest shadow noise, we made three shots at ISO100: normal, underexposed by -5EV and underexposed by -10EV! Patches from all three shots were analyzed to compile an SNR curve spanning 13 stops (down to 0.02% luminosity (which is RGB 0.05/255 and sRGB 0.6/255 aka perfect black)).

The surprising result is that at deepest shadows, the D5000 outperform the D700 by 2 dB and the K-x by even 5 dB. This should translate to about 0.5 EV more dynamic range for the D5000, and about 1.5 EV more dynamic range for the K-x, when compared to the D700. DxO does indeed confirm more dynamic range for the D5000 (12.5EV) compared to D700 (12.2EV). In combination, this is a confirmation for the "13EV or better" dynamic range claim I made in my earlier blog article.


3. Dynamic range (revisited)

I decided that this isn't the full story. Numeric results of measurements of noise are one thing. Plausibility checks are another.

(you must click the image and then select "O" (original size) to use this chart!)

The above chart contains various (small) noise patches from all cameras and ISO values. I even added some Pentax K-7 patches for comparison (Note: the K-7 has more pixels). Towards the end of this article, you'll find links to all original test shots suitable for further examination.

A quick examination of the patches at ISO 100 and -10EV shows that the D700 wins hands-down: better color accuracy, better readability of letters and better contrast. It sure looks slightly more busy (more noise) but the noise looks more fine grain too. More fine grain? Yes, the noise from the D5000 and K-x look coarser than the noise from the D700 or K-7. But noise should be statistically uncorrelated and look always fine grain (except for pattern noise).

Good detail note: all three cameras have no visible pattern noise.

Obviously, the sensor of the Nikon D5000 and Pentax K-x (and I guess it is the sensor rather than the firmware) plays some tricks with the signal in deepest shadows: there seems to be some sort of deep shadow noise reduction at work (like binning dark pixels) which leads to softer detail and a lower noise measurement.

Therefore, I conclude that the excellent dynamic range measurements of the D5000 and K-x are partly due to sophisticated signal processing, possibly on the sensor itself.

However, even taking this disclaimer into account, we can say that the deepest shadow reproduction of all three cameras play in one league: e.g., look at the 153 letters in the -10EV samples and compare to the K-7 (-9EV only) where the letters aren't legible anymore.

I conclude that by dynamic range, taking all information into account, the cameras rank as follows:

1. Nikon D700 (#3 by lab test)
2. Pentax K-x (#1 by lab test) and
   Nikon D5000 (#2 by lab test)

and are all very close.

The ISO12800 patches roughly confirm the numeric lab results. A K-x at ISO12800 and a K-7 at ISO6400 do roughly have the same noise while the K-7 keeps a slight resolution advantage even at such high ISO values.


4. Conclusion

Traditionaly, there is a one stop difference between full frame and APS-C. Temporarily, this sensor (Nikon D5000, Pentax K-x, supposed to be a Sony Exmor sensor) fills the gap (towards a Nikon D700) with respect to dynamic range while the difference remains with respect to high ISO noise.

This means that the D5000/K-x sensor has the same sensitivity to light as usual (as the D700) but has significantly reduced read-out noise.

The Pentax K-x may have a slight advantage over the Nikon D5000, esp. at very high ISO values. At the same time, this sensor (or firmware library) seems to include raw data alteration which makes the numerical analysis even more difficult, even when done in the DxO way. The time for true signal measurements has come, defining random noise as the sample variations of the signal and fixed pattern noise as the difference of the mean value with the ideal signal.

Lab tests (our own and the ones published by DxO) make the D5000/K-x have better dynamic range than the D700. But this is due to the limited testing methodology. D700 still has the better dynamic range, but by a small margin only.


5. Further reading

Access to full sample shot material:

• Pentax K-x test shots (full size)
• Nikon D700 test shots (full size)
• Nikon D5000 test shots (full size)
• Lumolabs: Welcome and testing methodology

Enjoy! :)

Lumolabs: Pentax K-x vs. K-7, sensor and video

Pentax has recently released a new SLR, the Pentax K-x. And while it is positioned at the entry-level market and very competitively priced, it is yet rumoured to have a very good noise performance.

After having done all my lab tests, I may say that the rumors are not true.

The truth is that the K-x may be the 35mm SLR camera which has the best high ISO noise and dynamic range performance to date. This isn't "very good". This is outstanding!

This is my concluding summary which is based on the following individual articles:

• Lumolabs: Pentax K-7 HD video quality
• Lumolabs: Pentax K-x HD video quality
• Lumolabs: Pentax K-7 sensor quality
• Lumolabs: Pentax K-x sensor quality

Noise and Dynamic Range comparison:

At the top of the article is a compilation of various gray sample patches for both cameras, for direct comparison. The patches are from linear raw files (cf. "further reading" at the end of the article).

The resulting 18% gray level chart is like this:


Signal to noise ratio of 18% gray luminosity and color temperature 2900°K (halogen tungsten). Using manufacturer ISO stops 100, 200, 400, 800, 1600, 3200, 6400, 12800. The interpretation of results is the same as for the corresponding graphs on dxomark.com. E.g., print-normalization is for 8 megapixels. The dotted lines indicate the slope for pure photon shot noise.

Obviously, the K-x has no true ISO 100 and both cameras reduce noise even in RAW at ISO 3200 and higher. The ISO sensitivity of the K-x seems to be slightly higher, like at ISO 100, true ISO were more like 87 for the K-7 (DxO's value for the K20D) and 105 for the K-x. However, the above curves have not been left/right-shifted to take this into account.

Gray level noise at ISO 1600/3200 for the K-x is about the same as at ISO 1000 for the K-7. While gray level noise at ISO 1600 and 3200 are about the same for the K-x, there is a minimal loss of resolution when looking at the pattern part in the full test charts. Nothing serious, though.


Signal to noise ratio (SNR) for the Pentax K-7 and K-x. Full measurement for various luminosities and ISO settings at color temperature 2900°K. Measurement similiar to dxomark.com. The dotted lines indicate the slope for pure photon shot noise. The flattening at 30% gray and brighter is believed to be due to systematic measurement errors like imperfect gray patches. The dashed curves for the K-x have been properly normalized to match the higher sensor resolution of the K-7.

The curve for K-7 only and test images are at:
Full SNR Pentax K-7

The curve for K-x only and test images are at:
Full SNR Pentax K-x

The K-x/ISO 200 and K-7/ISO 100 curves are almost identical down to 1% luminosity.

The full SNR graph clearly exhibits the true strength of the K-x sensor: it maintains the good SNR at low luminosity levels. This is an indication that the read-out noise from this sensor is very low.

Therefore, the K-x sensor outperforms the K-7 in low light situations whereas the K-7 outperforms the K-x in good light. This is further confirmed by the better resolution and more artifact-free images from the K-7.


Video:

The quality from HD video is very good. The resolution is as high as the 720p mode allows. It somewhat more moiré and color moiré artifacts than the K-7 and therefore, may not exactly match its analog and film-like quality in 720p mode. But it is very good nevertheless.


Conclusion:

The Pentax K-x has a sensor which rivals the best. That Pentax makes it available in the entry-level class is a good thing. On the other hand, the Pentax K-7 excells in many respects and even its noise performance isn't bad. It is in line with the rest of the competition which is beaten by the K-x in this respect now.


Pentax K-x: "Editor's choice" (entry level, available light)
Pentax K-7: "Editor's choice" (semi professional)



Further reading: Lumolabs testing methodology.

Lumolabs: Pentax K-x sensor quality

The Pentax K-x is an incredible machine for an entry level SLR. Here, I will look at the image quality which its sensor can produce.

In my lumolab testings, I will not report about ergonomics or lack of features etc. The internet is full of this easily obtained information and I will refrain from duplicating it here.


Test chart results:

The photo at the top of the article is an ISO test shot taken at ISO 1600 and color temperature 2900°K. It is a linearly converted RAW file (cf. "further reading" at the end of the article). Go to the gallery (click the image) to have a look at all test shots, available at original full size.


ISO resolution test chart using FA 31 Ltd. at f/4.5. The inner part is 4x. The Nyquist limit is at "7.1" in the inner part. Watch the original at 100% size.

The K-x resolves down to the Nyquist limit. However, it exhibits color moiré and false demosaicing at the limit frequency. The anti alias filter is very weak or absent as it allows for moiré down to three times the Nyquist limit. Color moiré is visible for textures at the Nyquist frequency.

E.g., note that the "7" patch has false demosaicing and strong color moiré. The same is visible from the zone plate chart. The K-7 doesn't show this in comparison.


Zone plate test chart using FA 31 Ltd. at f/4.5. The big circles have a resolution limit of 1280 LW/PH. The smaller ones are 2x and 4x. The 4x circles at above ~4000 LW/PH have uncolored printing moiré. The Nyquist limit is at 2848 LW/PH which is about 55% into the smallest circle. Watch the original at 100% size.

The zone plate chart of the K-x has false colors (fringing) already at half the Nyquist frequency and "green blobs" at three-quarter of the Nyquist frequency, followed by heavy color moiré at the Nyquist frequency exactly. The latter two effects are limited in spatial frequency space but the fringing is kind of disappointing.

While most testers will not notice the effect and welcome "the good resolving power of the K-x", which "leaves no resolution advantage to the K-7" (anticipated quotes from future pseudo tests), I personally would have preferred a stronger anti alias filter.


Numerical lab result:

The numerical evaluation of all noise charts (the full SNR plot) is as follows:


Signal to noise ratio (SNR) for the Pentax K-x. Full measurement for various luminosities and ISO settings at color temperature 2900°K. Measurement similiar to dxomark.com. The dotted lines indicate the slope for pure photon shot noise.

It is possible to derive both dynamic range and noise from the graph. If extrapolating the 0db point for ISO 100 at luminosity 0.01%, then the resulting dynamic range is 13.3 EV (print-normalized to 13.6 EV). E.g., DxO tests the print-normalized dynamic range of the K20D to be 11.05 EV and of the outstanding Nikon D3X to be 13.65. The flattening at 30% gray and brighter is believed to be due to systematic measurement errors like imperfect gray patches.

The theoretical photon noise separation between neighboring ISO lines is 3dB. There are three effects which can be observed:

- The SNR at ISO 100 is reduced for luminance levels above ~3% and drops to the ISO 200 values. A sign that ISO 100 is no native IO value for this sensor. On the other hand, it is exceptionally high for luminance levels below ~3%, with a boost more like ISO 75 than ISO 100.

- The ISO 3200 line is only 0.5 dB separated from the ISO 1600 line. DxO labs found that this is due to noise reduction applied to RAW data at ISO 3200 and higher. Without such noise reduction, the SNR would obviously be about 2.5 dB lower. This smoothing is even stronger than for the K-7.

Overall, the gray level noise (the SNR at luminosity 18.00%) is very close to the competition (worse at ISO 100, same at ISO 200 and better beyond) while the black level noise (the SNR at luminosity 0.10%) is very small. The ISO 1600 curve provides about the same black signal than ISO 100 pushed +4EV.

I have not measured SNR for luminance below 0.04%. But from extrapolation one may deduce that the K-x has a dynamic range of about 13.6 EV which would be even an excellent value for a full frame camera.


Update - The K-x "bump" at 2%, ISO 100 (2009, October 29):

Because of the importance of the ISO 100 SNR curve at low luminosities for the outstanding dynamic range claim made for the K-x, I have evaluated available testing material again, with special emphasis on this bump.


Signal to noise ratio (SNR) for the Pentax K-x. Full measurement for various luminosities and ISO 100 at color temperature 2900°K. Measurement similiar to dxomark.com. The dotted lines indicate the slope for pure photon shot noise.

This graph is meant to study the "bump" at about luminosity 2% in the ISO 100 curve of the full SNR graph (cf. above). The full 12 EV test chart is compiled from two parts: one exposed normally, another underexposed by 5 stops.

The above plot is a reexamination of both parts, now separately evaluated. There indeed is a discontinuous step (by +1.8 dB) when going from the normal to the -5EV curve which I cannot currently explain. The flattening of the brightest parts looks the same and could indeed be due to imperfect bright print patches. This would imply an underestimation of the "bump" by another 1.7 dB leading to a possible overall overestimation of SNR by +3.5 dB in the dark part.

Even taking this correction into account though, the above plot still confirms an extrapolated 0 dB SNR point at 0.01% luminosity. Therefore, the conclusions made in the other sesctions are not altered by this detail examination.

(end of update)


Conclusion:

- Resolution: Full Nyquist 12.2 Mpixel resolution, some moiré, some color moiré, some demosaicing artifacts. Very weak or absent anti alias filter.

- Noise: Gray level 40.0 dB at ISO 100, 31.6 dB at ISO 1600, dynamic range (print-normalized) >13 EV.

The image quality is good at low ISO values and very good if shadows are pushed-processed. It is outstanding at high ISO values and sets the bar for 2010. I haven't tested the Nikon D700 but from the known results, I say that the Pentax K-x is seriously challenging the D700 in terms of high ISO noise and dynamic range. With a much smaller body, a smaller sensor and a much smaller price tag ... and video ;)

I award the Pentax K-x the following title:

"Dynamic range champion 2009 in the 35 mm body class".



Further reading:
- Lumolabs: Pentax K-7 sensor quality
- Lumolabs testing methodology.

Lumolabs: Pentax K-7 sensor quality

I have previously reported about the image quality from the Pentax K-7.

The corresponding blog articles are here:

• Tungsten high iso noise
• Comparative noise study K-7 vs. K20D
• Comparative resolution study K-7 vs. K20D

Here, I will set a level playing ground for future comparisons of the image quality obtained from various cameras.

In my lumolab testings, I will not report about ergonomics or lack of features etc. The internet is full of this easily obtained information and I will refrain from duplicating it here.


Test chart results:

The photo at the top of the article is an ISO test shot taken at ISO 1600 and color temperature 2900°K. It is a linearly converted RAW file (cf. "further reading" at the end of the article). Go to the gallery (click the image) to have a look at all test shots, available at original full size.


ISO resolution test chart using FA 31 Ltd. at f/4.5. The inner part is 4x. The Nyquist limit is at "7.8" in the inner part. Watch the original at 100% size.

The K-7 resolves down to the Nyquist limit with very little color moiré and false demosaicing. The anti alias filter is rather weak as it allows for moiré down to twice the Nyquist limit. Color moiré is under control though.


Zone plate test chart using FA 31 Ltd. at f/4.5. The big circles have a resolution limit of 1280 LW/PH. The smaller ones are 2x and 4x. The 4x circles at above ~4000 LW/PH have uncolored printing moiré. The Nyquist limit is at 3104 LW/PH which is about 61% into the smallest circle. Watch the original at 100% size.

The transition at the Nyquist limit is rather smooth (the printing moiré being stronger than the sensor moiré) with almost no color moiré.


Numerical lab result:

The numerical evaluation of all noise charts (the full SNR plot) is as follows:

Signal to noise ratio (SNR) for the Pentax K-7. Full measurement for various luminosities and ISO settings at color temperature 2900°K. Measurement similiar to dxomark.com. The dotted lines indicate the slope for pure photon shot noise.

It is possible to derive both dynamic range and noise from the graph. If extrapolating the 0db point for ISO 100 at luminosity 0.07%, then the resulting dynamic range is 10.5 EV (print-normalized to 10.9 EV). E.g., DxO tests the print-normalized dynamic range of the K20D to be 11.05 EV which is about the same. The flattening at 30% gray and brighter is believed to be due to systematic measurement errors like imperfect gray patches.

The theoretical photon noise separation between neighboring ISO lines is 3dB. There are two effects which can be observed:

- The SNR drops faster than required by photon shot noise at gray levels under about 1%. This reduces the dynamic range. Gordon B Good found that this is due to a rather large read-out noise caused by the variable gain amplifiers (VGA) integrated into the CMOS sensor chip.

- The ISO 3200 line is only 1 dB separated from the ISO 1600 line. DxO labs found that this is due to noise redauction applied to RAW data at ISO 3200 and higher. Without such noise reduction, the SNR would obviously be about 2 dB lower.

Overall, the gray level noise (the SNR at luminosity 18.00%) is very close to the competition while the black level noise (the SNR at luminosity 0.10%) is rather large. This is of concern if brightness needs to be pushed in post processing. Interestingly, the ISO 1600 curve provides a better black signal than ISO 100 pushed +4EV.


Conclusion:

- Resolution: Full Nyquist 14.6 Mpixel resolution, weak moiré, very weak color moiré, nearly no demosaicing artifacts.

- Noise: Gray level 40.5 dB at ISO 100, 28.1 dB at ISO 1600, dynamic range (print-normalized) 10.9 EV.

The image quality is excellent at low ISO values and if shadows aren't pushed-processed, good at low ISO values otherwise and in line with the 2008 competition at high ISO values.


Further reading: Lumolabs testing methodology.

Lumolabs: Pentax K-x HD video quality

The Pentax K-x is an incredible machine for an entry level SLR. Here, I will look at the quality one can expect to obtain from its 720p@24Hz HD video capture mode.

In my lumolab testings, I will not report about ergonomics or lack of features etc. The internet is full of this easily obtained information and I will refrain from duplicating it here.

The above is a frame from a dumb sample video, available here:



Test chart results:


Video frame from 720p HD mode. ISO resolution test chart using FA 31 Ltd. at f/4.5. The inner part is 4x. The 720p Nyquist limit is at "8.5" in the outer part.

Watch the original at 100% size.


Zone plate test chart. The big circles have a resolution limit of 1080 LW/PH. The smaller ones are 2x and 4x. The Nyquist limit is at 720 LW/PH which is about 67% into the big circle. Watch the original at 100% size. The sampling frequency is clearly visible by the position of the four false color disks positioned at an 70% radius. The false color at and remaining artefacts beyond the sampling frequency is due to a missing video anti alias filter.

Note that the false color artifacts are significantly more intense than from the K-7, overall and esp. at 45°.

A similiar image for the Canon 5DmkII is visible here: Canon 5DmkII zone plate test.


Rolling Shutter Test:


Panning left and right to evaluate the rolling shutter effect.

Note that the sensor of the Pentax K-x is read out in the opposite direction than that of the Pentax K-7, like bottom-up rather than top-down.

In comparing with the K-7, please note that the panning speed is not exactly equal. The magnitude of the rolling shutter effect is proportional to the panning speed. Also note that the K-x video has slightly more blur. Lightning condition and aperture has been the same, though.

Some testers have stated that the K-x has a stronger rolling shutter effect than other cameras. I cannot confirm this. Maybe, the opposite direction of skew disturbed the viewing habits of video testers ...


Conclusion:

The Pentax K-x delivers very good HD video quality. It has color moiré artifacts close to the Nyquist frequency which are due to subsampling without an anti alias filter. The artifacts are strong and not so nicely confined to a close neighborhood around the sampling frequency. So, in real footage one has to expect to see some textures with color moiré. This is a problem of all SLRs though, specifically those sampling at natively 720p.

The effect seems to be about that of a Pentax K-7 along horizontal and vertical lines. But the K-7 has no such artifacts along diagonal lines which may point to the fact that it uses more and differently aligned pixels in its subsampling procedure. Obviously, the K-7 scans 1024 lines (using 864 in 16:9 format) whereas the K-x only scans 720 lines.

Interestingly and unlike the K-7, the K-x has no magenta/green fringing and no double seam effect along near vertical lines. The subjective effective resolution in 16:9 is about 1350x717 or 1.0 MPixel. This is an excellent value not achieved by consumer HD camcorders. It even surpasses the 1280 limit ;) The K-7 has slightly less resolution in the horizontal direction but much better resolution along diagonal lines.


Further reading:
- Lumolabs: Pentax K-7 HD video quality
- Lumolabs testing methodology.

Lumolabs: Pentax K-7 HD video quality

I have previously reported about the HD video mode in the Pentax K-7.

The corresponding blog articles are here:

• As a movie camera -- Part I, Part II, Part III

Here, I will set a level playing ground for future comparisons of the video image quality obtained from various cameras.

In my lumolab testings, I will not report about ergonomics or lack of features etc. The internet is full of this easily obtained information and I will refrain from duplicating it here.

The above is a frame from a dumb sample video, available here:
Bavarian Camels (K-7 version).


Test chart results:


Video frame from 720p HD mode. ISO resolution test chart using FA 31 Ltd. at f/4.5. The inner part is 4x. The 720p Nyquist limit is at "8.5" in the outer part. The 1024p Nyquist limit is at "10.0" in the outer part. The color moiré shows that the 720p frames are downsampled from 1024p video frames.

Watch the original at 100% size!


Video frame from 1536x1024p HD mode. The 1024p Nyquist limit is at "10.0" in the outer part and "2.5" in the inner part. The resolved parts with distinct lines is about "8.0" in horizontal and "8.5" in vertical direction, corresponding to 1200x850 pixels in 3:2 or about 1200x717p pixels in 16:9 mode.


Video frame from 720p HD mode. The big circles have a resolution limit of 1080 LW/PH. The smaller ones are 2x and 4x. The Nyquist limit is at 720 LW/PH which is about 67% into the big circle. The Nyquist limit of the 1024p sampling is at 864 LW/PH which is 80% into the big circle. Watch the original at 100% size.
The sampling frequency is clearly visible by the position of the four false color disks positioned at an 80% radius. The false color at and remaining artefacts beyond the sampling frequency is due to a missing video anti alias filter.

A similiar image for the Canon 5DmkII is visible here: Canon 5DmkII zone plate test.


Rolling Shutter Test:


Panning left and right to evaluate the rolling shutter effect.

Note that the sensor of the Pentax K-7 is read out in the opposite direction compared to that of the Pentax K-x, like top-down rather than bottom-up.


Conclusion:

The Pentax K-7 delivers stunning HD video quality, specifically in 720p. It has color moiré artifacts close to the Nyquist frequency which are due to subsampling without an anti alias filter. The artifacts are strong but seem to be nicely confined to a close neighborhood around the sampling frequency. So, in real footage one has to really hit the "wrong" texture to see the effect.

The effect seems to be about that of a Canon 5DmkII along horizontal lines. But the Canon has no such artifacts along vertical lines, pointing to supersampling within lines and line skipping. The Pentax K-7 does line and row skipping. Obviously, the 5DmkII scans 1053 lines whereas the K-7 only scans 1024 lines.

Moreover, in 1024p along nearly vertical edges (cf. the 1024p resolution test chart), one can see the magenta/green fringing and a double seam effect. This is much less visible in 720p though. Additionally, it may be possible to cure it in post processing. The subjective effective resolution in 16:9 is about 1200x717 or 0.9 MPixel. This is a good value actually not achieved by consumer HD camcorders.

Due to its supersampling applied to 720p video, footage from the K-7 looks more cinema-like and analog than footage from entry-level dSLRs.


Further reading: Lumolabs testing methodology.

Lumolabs: Welcome and testing methodology

Welcome to Lumolabs.

I never was really satisfied with the big lab tests (dxomark.com and dpreview.com) and really was disappointed by print magazine and other ezine tests. So, I decided to set up my own testing laboratory, based on experience as a photographer, insight as a physicist, software writing and image processing skills and patience.

For the time being, I am not challenging the big labs and confine my ambitions to the following areas:

1. RAW file image quality, in particular noise, dynamic range and resolution.
2. Video frame image quality, in particular resolution and artifacts.
3. Pentax.

I am not looking into color accuracy (not even chrominance noise...) or the camera's JPG engine. Or autofocus, ergonomy, build quality, etc. I may do lens tests and other vendors later as well.


Let me provide you with a short summary of my testing methodology:


RAW file treatment

I use the RAW file from the camera (DNG preferred) and use Adobe Lightroom 2.4 (LR) to do the demosaicing. The standard settings must be altered in the follwing ways to get a neutral demosaiced 16Bit sRGB TIFF file:

- Gray card calibrated white balance (I use 2900°K halogen tungsten light).
- Blacks 0 (changed from 5)
- Brightness 0 (changed from 50)
- Contrast 0 (changed from 25)
- Sharpening 0 (changed from 25)
- Noise reduction Color 0 (changed from 25)

I then read the resulting 16Bit sRGB TIFF file into my own lumolabs software. I properly convert the sRGB response curve (which isn't exactly a gamma curve) into linear colors and 18% gray is RGB 117.6/255.


Taking test chart photos

I then take test chart photos with controlled manual settings, including manual focus. About the slowest shutter speed is 1/15s.

Some think that noise test shots must be taken in low tungsten light. I agree for the tungsten part and I use it. I disagree for the low light part, though. A short exposure is a perfect approximation to low light because the read-out time of the sensor is longer than 0.1 seconds anyway whatever fast be the shutter. So, only if I wanted to study exposure time longer than, say 1/5s would low light be able to have an influence. In consequence, I don't publish exposure times shorter than 1/10s. Additionally, except for initial focus, I avoid using live view in noise tests to not overheat the sensor.

One of my test charts is the zone plate chart useful to evaluate anti alias filter and Bayer mosaic filter artifacts. It is shown in the beginning of the article. It is allowed to download it for own testing purposes, providing proper credit is given.

Other testing charts are an ISO-12233 resolution chart which I modified to include inner parts of 4x the resolution. Another chart is the noise testing chart with defined gray and color patches. All charts are printed on A2 paper using a high end photo printer. There are minimal printing artifacts visible at and beyond 4000 LW/PH (line widths per picture height). They do not disturb the testing results though.

The density range of the printed noise test chart is about 7 EV. So, I take a second shot at -5EV and obtain a combined test chart of about 12 EV dynamic range (luminance range 0.02% to 100%). Which immediateley turned out to be outperformed by the recent Pentax K-x ;)

My software will search for patches of minimal variance to exclude the effect of scratches and the like which may be present on the printed test chart. I am not sure though that there aren't some invisible defects below the -40dB range. They do not disturb the testing results though, except maybe for very bright patches.


SNR, noise and dynamic range

I am unrelated to DxO Labs, Boulogne, France. However, whereever I found their methodology to be appropriate (cf. dxomark.com), I adopted it. I disagree on some of their methodologies but some are best practise to be followed. My biggest concern with DxO is their lack of examination of influence of spatial frequency dependencies. They only "correct" their results for resolution effects as to be expected from pure photon shot noise. IMHO, this isn't good enough. I am currently working at a new testing methodology to overcome this. For the time being though, I am happy to adopt DxO's pixel-level measure methodologies.

It is therefore important to understand the SNR [dB] figure. It is explained here: SNR.

Another important detail is the print normalization: Noise, dynamic range etc. are all improved by downsizing an image. Still, measures take place at the varying resolution of the sensor. Like DxO, I use a "print-normalization" calibrated to a 8 MPixel resolution. The normalization formulae are here: print-normalization.

SNR [dB] can be easily understood by using the follwing hints:
- A patch of basically random pixels has an SNR of 0 dB.
- A decrease of light by 1 EV, doubling the ISO, going to a 50% darger region in an image or doubling the number of pixels all amount to a change of SNR by -3dB.
- Going from 1.53 crop APS-C to full frame amounts to a change of SNR by +3.7dB. So, 3dB is a lot ...

My full SNR curves can be directly compared with the DxO mark tab "Full SNR". Note however that DxO uses noise patches made from glass, has a different light source most importantly at a different color temperature and uses a different raw converter. Also, in derived measures, I don't include ISO sensitivity variance and possible raw data noise reduction (smoothing).

The dynamic range is the luminance level where SNR reaches 0dB, converted to f-stops and normalized for resolution. Note that the 0dB level is arbitrarily choosen by DxO and is resolution dependent. They formula-correct for resolution dependency but fail to understand that the full dynamic range must be measured at a much lower resolution. I plan to address this issue.


Video frame tests

The video frames studied in the video section are extracted using the Quicktime Pro "export as an image" feature. Because the video uses the camera's JPG engine, here are the parameters:

- Pentax: WB manual (2900°K), "Natural color profile preset", all other parameters at default values (like noise reduction and sharpness -1).


Enjoy the tests :)

Pentax K-7 in German magazine test

I don't normally copy/cite content from other sources. But I am going to make an exception now. I cite numeric test results which were recently published by German photo magazine ColorFoto (ColorFoto 9/2009). I do so because there are so few sources around which offer a comparison of the K-7 image quality when brought to lab tests.

You may read more about the K-7 test done by ColorFoto by fetching a printed copy. You may probably be able to download the full text after the printed copy went out of stores, by going here: www.colorfoto.de.

So, besides citing their numeric image quality test results, I am only going to say this much: They liked the K-7 a lot!


Cited test results:

Test (ISO)	Pentax K-7	Pentax K20D	Nikon D300	Canon D50	Olympus E-3
Resolution 100 [LP/PH]	1327	1310	1253	1327	1146
Resolution 400 [LP/PH]	1325	1294	1248	1326	1113
Resolution 800 [LP/PH]	1318	1302	1189	1286	1052
Resolution 1600 [LP/PH]	1295	1287	1144	1191	1053
Texture loss 100	0.0	0.0	0.2	1.1	0.7
Texture loss 400	0.0	0.0	0.2	1.2	0.7
Texture loss 800	0.0	0.1	0.3	1.0	0.9
Texture loss 1600	0.1	0.2	0.3	0.9	1.1
Noise 100 [VN]	0.8	0.8	0.7	0.6	0.9
Noise 400 [VN]	1.5	1.5	0.8	0.9	1.7
Noise 800 [VN]	2.6	2.4	0.9	1.2	2.7
Noise 1600 [VN]	2.7	4.1	1.3	1.5	3.6
Dynamic range 100 [EV]	8.5	8.5	10.5	9.5	8.5
Dynamic range 400 [EV]	7.5	7.5	9.5	9.5	8.0
Dynamic range 800 [EV]	7.0	7.0	10.5	9.5	7.0
Dynamic range 1600 [EV]	6.5	6.0	9.0	9.0	6.5
AF + shutter latency at ~10 EV [ms]	390	280	270	280	360
AF + shutter latency at ~3.5 EV [ms]	580	1060	470	260	730

Notes:
Lenses used (image quality test / AF test):

• Pentax DFA 100 f2.8 Macro / DA 18-55 f3.5-5.6 AL II
• Nikon AF 60 f2.8 Macro / AF-S 27-70 f2.8 G ED
• Canon EF 50 f2.5 Macro / EF 24-70 f2.8 L USM
• Olympus ED Digital 50 f2.0 Macro / ED 12-60 f2.8-4.0 SWD

Light values (EV) in AF tests are computed from quoted 3000/30 lx figures by myself.

The image tests have been run from the JPGs produced out of camera. The default setting of the K-7 (as used in the test) applies noise reduction starting at over ISO 800 only which explains the relatively good values at ISO 1600. Most other brands obviously already apply noise reduction at ISO 800 or below.

The ColorFoto lab tests may be unique in that they provide a measurement of the loss of texture (typically caused by aggressive noise reduction algorithms).

Therefore, one may have a careful look at the "texture loss" measurements. Pentax has none, Nikon has it somewhat under control and Canon is more like a mess. So, depending on how you weight noise vs. texture, either Nikon or Pentax would win in the noise/texture department. Dynamic range when measured from JPGs does always include the tone curve applied. As there are plenty of tone curve parameters to play with, esp. on the K-7, I don't know how useful the corresponding measure is. I included it for the sake of completeness of citation.

More interestingly though, the K-7 sensor seems to have no significant difference to the K20D sensor (to be confirmed by raw file lab tests though) and the K-7 JPG engine seems to offer subtle improvement in resolution and noise/texture. This is in line with what I found out myself (cf. my other blog articles). And, this test sharply contradicts another blog article ricing high concerns...

Another figure being noteworthy of course is the AF measurement. In low light, the K20D AF.S figures were last in the field. The K-7 now seems to be more comparable to Nikon or Olympus with Canon still winning the competition. But the results are to be taken with a grain of salt: The difference of figures in full light between K-7 and K20D showcase errors in the measurements.


Conclusion

The first lab test of the K-7 image quality I am aware of confirms my early impression: image quality is on par with K20D or better. The JPG engine still produces a lot of noise but preserves a lot of texture detail too, compared to its direct competition.

LumoLabs: Busting the alignment myth

This will be a special feature for hard core falconeye followers ;)

It all started with the exciting new feature of the Pentax K-7 camera which can produce true HDR images in-camera (it takes 3 shots, 3 exposure values apart from each other, and creates a single, tone-mapped or blended image from the sequence). It does it so well, esp. in the medium setting (as opposed to strong) that a limitation of the feature does actually hurt: you require a tripod to use the function.

The general opinion why Pentax left out the alignment step from their HDR function is that it is a processing power-hungry computation not easily done in-camera.

Not my opinion, though. I felt that Pentax has left out 10% of the implementation which reduces 90% of the functionality. Shouldn't it be the other way round?

Now, opinion isn't proof.

So, I implemented my own alignment operator, benchmarked it and compared its quality against the state-of-the-art in HDR.


The algorithm

The implementation is based on an algorithm whose computing time increases linearly with image size and is constant with amount of distortion. Note that I did not attempt to cope with the alignment problem known in panorama stitching, i.e., I don't do SIFT key extraction, I don't correct for lens distortion, I don't project onto a sphere before alignment, etc. pp. However, what I do is correct for shift and rotations which is a mathematical first order approximation to the latter and rather exact for small shifts and rotations.

The implementation uses a monochrome quad tree and high bit depth. The coding is in Java. It isn't based on anybody else's intellectual property.


The benchmark

I benchmarked the algorithm with a 5 image HDR from Munich Siegestor. It had distortions of up to 20 pixels and needed rotation as well. The source images haven't been ideally sharp (e.g., 1/25s and wide open with 15mm). And no program created a perfect alignment. So, I considered this example be adequate. The images were 14.6 MPixel JPG images.

The processing times on a Mac Mini (Early 2009), one processor used, are as follows:

• Single alignment: 175 ms
• Alignment of all HDR images: 700 ms
• Reading of all images from disk into Java heap: 16 s
• Shift-turn and write images to disk: 34 s
• Total, disk to disk (70 MB transferred), 5 images: 50 s

The K-7 has a dedicated image DSP and can certainly rival this. E.g., it can JPG-compress a 14.6 MPixel image in about 100 ms only!

Because the HDR function within K-7 already has created the required image structures in its 2 GB memory, it would be conclusive to assume that addition of an auto-alignment feature to the HDR function would add less than an extra 1/2 second to overall operation time.

If processing speed isn't the reason, so maybe it is quality? This must be looked at. In particular as some of the alignment operators I compared with took several to nearly 10 minutes to complete.

The quality

I've run several alignment operators and come up with the following ranking:

1. Photoshop CS3; PhotoAcute ("normal alignment")
2. Falk Lumo Operator (as of this blog article); PhotoMatix 3 ("by matching features")
3. PhotoMatix 3 ("by matching features"; "reduce ghosting")
4. PhotoMatix 3 ("by correcting horizontal and vertical shifts")
5. No alignment

All pre-aligned images have been read into Adobe Photoshop CS3, either by HDR merge (without further alignment) or by opening the 32 Bit .hdr-file written by PhotoMatix. Tonemapping was done in Photoshop CS3, using the "Equalize Histogram" method. The latter isn't best but as it has no parameters, I thought it would make for a good option in a comparative study. Finally, the result was studied to derive the above ranking. Which is entirely subjective!

Below are the two samples from category #2. Please, visit the gallery to view the other samples, too. Note that all sample images have been resized to 6 MPixel.

Fig.1 No alignment


Fig.2 PhotoMatix


Fig.3 Falk Lumo Alignment Operator (as decribed here)

Take me to the gallery

Conclusion

The myth is busted. There is no reason to not include auto-alignment into the next firmware release of the K-7 HDR feature. In less than an extra second of processing time, about PhotoMatix quality can be provided. Make it so!

K-7 Barbecue

K-7 Grillen

In order to celebrate the end of the Pentax K-7 alpha test, another tester from Munich and myself organized a little barbecue.

I've cut a little movie from files found on my K-7 and some shots from friends (in German language).

K7Grillen (K-7 Barbecue) from falconeye on Vimeo.

Enjoy :)


Btw, the green light at the end is the K-7's AF assist light.

Pentax K-7 Concluding Review Report

Fig. K-7 getting wet feet while recording a movie (aperture blades stopped down).


This is my concluding review report about the Pentax K-7 dSLR camera hitting stores next week (last week in Japan).

It is based on my experience throughout the past month, after Pentax Germany was so kind to ask me to test their new flagship camera. It is today that I have to return the camera :(

You may read about my detailed findings in my various blog articles found here:

• I am Pentax K-7 Alpha Tester :)
• In the rain
• Its continous autofocus -- Part I, Part II
• Its precision autofocus
• Tungsten high iso noise
• Comparative noise study K-7 vs. K20D
• Comparative resolution study K-7 vs. K20D
• As a movie camera -- Part I, Part II, Part III
• Ergonomics

Again, I am not going to repeat the spec sheet of the camera. Please, go to

• pentaximaging.com K-7 website
• K-7 user manual
• DPReview web preview/review

to get the full list of features. Here, I'll just share my opinion about the product. First, I am going to break up my impression with various "use cases" in mind.

1. General comments

The Pentax K-7 is in a class with only five competitors (*). It is Nikon D5000, D90, D300, Canon EOS 50D, and Pentax K-7. The price range covers 730$ (D5000), 950$ (D90), 1200$ (50D), 1300$ (K-7), 1700$ (D300). However, as the K-7 is at launch price now, it is expected that the street price of the K-7 is to drop below 1000$ later this year and would be priced roughly like the D90.

So, let me quickly compare the K-7 against the other four models:

• K-7 vs. D5000
  Pro: Better LCD, Faster/better shutter, much better VF, SR, WR, metal body, 15MP
  Con: Heavier, no tilt LCD


• K-7 vs. D90
  Pro: Faster/better shutter, slightly better VF, SR, WR, full metal body, 15MP
  Con: none


• K-7 vs. 50D
  Pro: Slightly better VF, video, SR, WR
  Con: 1/180X, no double cross center AF sensor, no tethering


• K-7 vs. D300
  Pro: Lighter, video, SR, 15MP
  Con: slower and no 150k shutter, 1/180X, no 51 AF points (11), no 1005 zone metering (77), no tethering

_____
(*) defined by dSLR, 12+ MPixel APS-C, LiveView, ISO3200+, 3.5+ fps
SR: in-body stabilization (shake reduction)
WR: sealed body and kit lenses for weather resistance

This little list is not meant to rank the competition ;) But it shows that the K-7 is very interestingly positioned. Let's say that the D5000 seems to be an interesting camera but is positioned below the D90 which is a more serious competitor, but still somewhat below the class of the K-7. The only true matches in class are 50D and D300, where D300 actually is somewhat above. However, if video or in-body stabilization or bad weather-resistance are required then there simply is no match for the K-7. The only thing we need to check out is whether K-7 delivers on its promise. If it does then it has no real competition (yet).

Having said this, I'll leave the feature list comparison for a more meaningful consideration of strong or weak fields of application. Each of the following fields gets a score within 1 to 5 stars (category for digital 35mm mount SLR).

Throughout, this is based on the following judgements:
- High ISO noise performance is on par with the current state-of-the-art for APS-C (ignoring differences of a 1/3 stop). The K-7 will look both more noisy and more detailed at the pixel level compared to the competition above. Some think that this renders more beautiful images when printed. Others think that buttery images at high ISO are better. I think that the differences aren't significant enough to be important but I prefer to keep noise and detail for later processing. Full frame delivers one full additional stop though.
- Autofocus is significantly improved compared to previous models from Pentax and at or above average. But still no match for the best in its class (D300).
- 15 MP resolution is fully applicable when using good glass.
- Everything what you can read in the separate articles as given above.


2. Landscape / Cityscape photography
★★★★★
Actually, the K-7 is a stellar performer here and K20D already scores high. The relatively lightweight body, stellar image quality at low ISO in combination with available stunning prime lenses makes this the best choice short of a (heavier) full frame 20+ MP camera. A function for automatic horizon just makes it perfect.

3. Wildlife
★★★☆☆
It scores high like for landscape, but I remove two stars for the following reasons:
- fast and/or long glass is extremely rare and expensive, and a tele converter is lacking.
- AF.C autofocus is good (and much better than in previous Pentax cameras) but may still miss a shot in action-loaden situations (flying birds, predator attack).
Note that the first point is not a weakness of the camera itself.

4. Sports and Action
★★★☆☆
Same rationale as for wildlife. Also, there are faster, machine gun type bodies.

5. Wedding
★★★★☆
The K-7 is the perfect APS-C body for this kind of shootings and additionally can provide stunning HD footage. It is a robust tool and sufficiently fast, too. However, in situations where light is not optimal, a full frame body with fast glass can be a better option.

6. Family
★★★★☆
Much like wedding. But ease of use and the fact that full frame would be overkill adds a star. Very young active kids or pets can still be challenging though and costs a star.

Btw, I don't agree with some other reviewers that the K-7 underexposes. If I would, I would subtract another star here. I agree that K-7 tends to expose darker than what is seen in other cameras, but for a reason. Easily studied with its live histogram. E.g., a burned highlight in the extreme quarter decreases exposure from 1/25s to 1/30s. So, it isn't true that K-7 underexposes to rescue irrelevant highlights. It just takes into account that bright levels clip where dark levels don't. Just work with +1/3EV if you never adjust levels.

7. Street and People Photography
★★★★★
Can't be beaten. Light-weight un-obstrusive and able to cope with almost every foreseeable situation. A smaller camera (like K-m or non SLR) may be interesting but would be less rugged. The improved metering performance with highlights and with flash are important improvements coming with the K-7 (for night life).

8. Travel
★★★★★
Same rationale as above. Just keep an eye on your stuff, though. An SLR may not always be the best option. Depending on your priorities.

9. Portrait and Studio
★★★★☆
The K-7 is almost perfect. The lack of a tethering option costs a star, though.

10. Movies
★★★☆☆
I judge the K-7 to be the second most interesting SLR offering video (with Canon 5DmkII being no.1 which would get 4 stars). The missing 2 stars are:
- No supersampling of full 15MP down to 1080p
- No videographer form factor/controls/EVF available with working Contrast AF
(taking the strengths (ISO, DoF etc.) into account.)

What sets it apart from other offerings are a "better than 720p" mode @30fps, uncropped 3:2 video, stereo, bearable jello effect, some manual control (aperture, EV compensation, exposure lock), no motion-compression artifacts. Of course, full manual control, electronic viewfinder and a fast contrast AF are all missing.

11. HDR and panoramas
★★★★★
The built-in HDR feature makes any other camera score 4 stars or less only. But Pentax missed the chance to align the images in-camera which would have been straightforward to do. The feature works great, otherwise. Moreover, the K-7 offers perfect control to do HDR panoramas. Live view with grid, exposure bracket and horizon control are an additional help.

12. Macro photography
★★★★☆
Perfect control available. A higher resolution LV would be an improvement but doesn't currently exist on the market. I subtract a star because an automatic focus series for focus stacking would be great. AFAIK, it doesn't currently exist on the market for no reason.

13. Astro photography
★★★☆☆
LiveView is of great help and controls are perfect. Missing though:
- Tethering option.
- Dark frame subtraction shut off for exposures > 30s not possible.
- Crop of FoV compared to full frame, depending on the type (FoV) of telescope.

14. Final Verdict
Four stars is the average and my conclusive score. If you look at my criteria, there probably will be no camera scoring at 5 stars (smarter beats bigger). Certainly not its direct competitors, the 50D and D300. I like both cameras as well and they have different weaknesses and strenghts. But I like the K-7 better. A contender for 5 stars would be Nikon's D3X, if it were 1/3 lighter and had video.

So, the K-7 not only feels like a lot of fun to use, it is a very good proposition on the current market. The best ever made by Pentax and a bigger step forward for Pentax than they did whith the (already very good) K20D. Compared to the K-7, the K20D feels old already.

So it does deliver on its promise indeed which means:

Pentax K-7

★★★★☆

Editor's Choice

"APS-C SLR camera"

(5 stars not assigned in category; as of 2009, July 1st)

A sunny sunday

Enough testing. The Alpha Test is going to end anyway soon. Just relax, sit outside in the garden and have a good time. Which doesn't mean that I cannot press the shutter once in a while ;)


And then I saw a red balloon in the distance.

Shot freehand with a Pentax K-7 and a FA* 300/4.5 lens. You may click on the image above to view it in original size and see that the opening image actually is nothing but a 100% crop from this very image. You actually can see heads more than 3 km or 2 miles away (as I later computed).

Enjoy ;)

K-7 and ergonomics

This is just a short essay about 5 ergonomic details in the K-7 which may create worries.


1. The omission of the Shake Reduction button

The K20D has a clearly visible SR button which is missing in the K-7. The following sequence is required in the K-7 to switch SR on or off. First, lets define how I call the buttons around the OK button: "8", "4", "5", "6", "2", like on a numeric keypad, with "5" being the OK-button itself ("8" is the drive button on top of "5").

[INFO] -> [2]/[6]{0-6} -> [RearDialClick]

{0-6} means that the button must be pressed 0 to 6 times, depending on where it was before. Assuming you only switch SR, it is just two buttons, [INFO] -> [RearDialClick]

Because SR is switched off automatically, e.g., on a tripod with remote control, this omission is no big deal.


2. The omission of the exposure bracket button

The K20D has an exposure bracket button which serves to quickly enable exposure bracket using the two dials to set #images and EV distance in between.

Assuming you always use the same exposure bracket (e.g., 5 exposures 2EV apart), the enabling sequence is as follows:

enable: [8] -> [4] -> [4] -> [5]
disable: [8] -> [6] -> [6] -> [5]

So, it is 4 button presses to activate and de-activate. If used often, one can live withit. But it is a lot less fun to set than with the K20D. Again, this omission is no deal breaker though.


3. Pressing OK for AF selection

Not being a heavy user of AF point selection, I can live with pressing OK prior to AF point selection. A user which relies on AF point selection however, will not understand why the logics isn't inverted as soon as you dial into AF point "SEL" mode. Because now, a change of AF point is much more frequent than, e.g., a change of drive mode.

So I really hope that Pentax adds a custom setting which makes AF selection the default in "SEL" AF point mode where pressing OK acts like Fn.

-- UPDATE --
As of today (July 29, 2009), Pentax has released a firmware update (v.1.01) which adds exactly the behaviour as described above as an option. Now, AF point selection can be used like with a K20D (i.e., the OK button will act as mode switch, not as middle AF point selector).

Pentax, thank you for listening!
-- END of UPDATE --


4. The mode dial lock button (mdlb)

The mode dial of the K-7 on the left side controls mode such as P, Av etc. In order to prevent that it can be changed inadvertently, it got a button in the middle to lock it. It must be pressed in order to turn the dial.

I developped a technique using three fingers from my left hand: the index finger presses the lock while the two neighboring fingers (one is the thumb) turn. Any other technique including using two hands (the obvious choice) turned out to create headaches.

There are two problems with the mdlb:

• Engaging it will more probably lead to an inadverted change of the exposure meter mode (the level right underneath!) than the mode would change w/o the mdlb. And this inadverted change passes unnotices most of the time!
  Therefore, adding the mdlb and not removing the exposure meter mode level is a clear engineering mistake.
• They've put the video button as a mode
  So all of a sudden, mode changes are frequent. While it was ok to stay in Av mode for ages with, e.g., a K20D, you now have to always switch between video and Av modes. If you seriously use video, you'll soon do it blindly -- and change exposure meter mode sooner or later.

So, you better regularly check your exposure meter mode, and EXIF for photos said underexposed ;)

I consider the mdlb to be a real nuisance. Pentax, please, take it back! Or make it toggle so we can leave it unlocked permanently.

And by the way, making the video button a mode is a schnapsidee (crazy idea) ...

5. Focal length info

The info screen has changed. It is more useful now. But I found no way anymore to display the focal length of a zoom lens prior to a shot.

Overall

With the exception of the mdlb, I like the new interface. And I didn't want to discuss the RAW button ;) The info button grants easy access to many quick changes. So, despite some weak points, I consider the overall button ergonomics of the K-7 even better than that of the K20D. Anyway, I really like the ergonomics of Pentax, in particular their hyperprogram and manual focus shift philosophy.

K-7 as a movie camera -- PART III: Sample video

-> Link to part I

After all the preparation, I would like to share a short and uninspired video with you. And some thoughts about post processing ...

This is a short video sequence shot at 1536 x 1024 with a Pentax K-7 during an oldtimer car meeting earlier this year near Munich.

Pentax K-7 movie in 1080p from falconeye on Vimeo.

This video is nothing special. But I will use it to illustrate

Options for post-processing

1. The form factor.

720p video is 1280x720, 1080p video is 1920x1080, both in 16:9 aspect ratio. The native video capture is in 1536x1024 or 3:2 aspect ratio.

• 1536x1024 -> 720p: magnify by 83.33%, crop 8.00% from upper and lower edge each.


• 1536x1024 -> 1080p: magnify by 125%, crop 7.81% (100px) from upper and lower edge each.

There is no benefit in recording in 720p directly, except for a better control of framing (16:9 framing on rear display) and smaller file sizes. For 720p, the camera does the same supersampling to 83% size one would do in post-processing otherwise. On the other side, keeping the 1536x1024 material provides some more options for post-processing.

1536x1024 material is not suitable for direct presentation. Here, 720p is a better option.

2. Recoding.

Most video editing software will directly open the AVI file stored on SD card. Additionally, Apple Quicktime will open the file and Quicktime Pro allows to extract individual or all frames as images. Or to recode the movie, e.g., to MP4 AVC H.264.

Photoshop CS3/CS4 can open the AVI file directly as well and you get a video layer. There, you can do many image operations like you do for still images and recode, e.g., again to MP4.

After touching up the raw material, I used Adobe Premiere Elements for more video-oriented editing. On the Apple, MacOSX has something similiar on board, called iMovie.

3. Quality.

The K-7 captures stunning video quality. But it isn't good enough to justify the extra size coming with 1080p, compared to 720p. At least not without further touching up the quality.

Below, you'll see two frame images from the short clip above. The first is as out of the camera.

The second image is post-processed using my K-7 video IQ master (a program which I developed to defeat the "768-aliasing artifact"). The K-7 video IQ master is work in progress and yet unpublished. The basic idea is to use the insight about the submatrix as described in part I and try to correct some of the weaknesses in the original algorithm as built into the camera.

You may have to click onto the images to see the original size to study the difference. According to several opinions, the filtered footage has less fringing and less jaggy lines while still gaining (or at least maintaining) on overall detail (read: without becoming softer). It was used to create the 1080p clip in the opening of the article.

I hope that a forthcoming version of the K-7 video IQ master will be good enough to render 1080p footage to the same stunning quality we now see in 720p footage. And further improve on 720p quality. Btw, I very much welcome any comments on this topic.

As a side note. It is no problem to add motion blur to frames belonging to a panning action. Or tilt to remove the skew. Just open the corresponding video sequence in CS3.

Conclusion:

This shall conclude my three part article about the video capabilities of the Pentax K-7.

The video mode in the Pentax K-7 looks like a very promising proposition. It can produce stunning video quality, esp. in 720p. However, Pentax made a number of trade-offs to keep the camera affordable as a still camera (and it is a high spec camera already w/o video). Therefore, to achieve maximum possible quality in movies, a number of tweaks applied during capture and in post-processing are of help.

Enjoy your moving images :)

Further reading:

• Ned Bunnell's blog article about using a stereo microphone
• Disussion thread about K-7 video quality
• Discussion thread about K-7 and an external microphone (dosdan's posts starting at #11)

K-7 as a movie camera -- PART II: Controlling video recording

In part I, we have discussed the technical implementation of the video feature in the Pentax K-7.

Now, let's see how to make good use of it. Again, I'm not going to repeat the specification or user's guide.

At first glance, it seems to be very straight-forward: Turn the mode dial to movie and press the shutter! Ok, done this, been there. Now, for the more serious fun: how do we control shooting parameters?

The official answer by Pentax is: you don't! There is almost no manual over shooting parameters. But as always, there are back doors :)

Things to know:

1. You can set global parameters like pixel format, quality, shake reduction in the "video" menu (press the menu button when in video mode) and is not affected by all the nice settings you may have tweaked. E.g., forget about your Auto-ISO range ;)


2. Autofocus, aperture and E/V-compensation can be set prior to a recording. All three are defunct while recording. Of course, the camera won't complain if you change aperture or focus manually (read: mechanically). The focus in video mode is contrast autofocus by default. But you can switch to phase autofocus which is faster.


3. The exposure (with all its parameters) can be locked/unlocked before and during a recording, using the AE-L button.


4. EV values in video and still image modes seem to be the same.

Controlling exposure

Knowing the video exposure response curve is key in determinig and manually controlling an exposure in a K-7 video. It isn't published by Pentax but I researched them to be this:

Assuming an aperture is preset to a given value:

Light value [EV] at f/										Shutter	Sensitivity
1.4	2.0	2.8	4.0	5.6	8.0	11	16	22	32	[s]	[ISO]
0	1	2	3	4	5	6	7	8	9	underexposure	blng red
1	2	3	4	5	6	7	8	9	10	1/30	3200
2	3	4	5	6	7	8	9	10	11	1/30	1600
3	4	5	6	7	8	9	10	11	12	1/30	800
4	5	6	7	8	9	10	11	12	13	1/30	400
5	6	7	8	9	10	11	12	13	14	1/30	200
6	7	8	9	10	11	12	13	14	15	1/30	100
7	8	9	10	11	12	13	14	15	16	1/60	100
8	9	10	11	12	13	14	15	16	17	1/125	100
9	10	11	12	13	14	15	16	17	18	1/250	100
10	11	12	13	14	15	16	17	18	19	1/500	100
11	12	13	14	15	16	17	18	19	20	1/1000	100
12	13	14	15	16	17	18	19	20	21	1/2000	100
13	14	15	16	17	18	19	20	21	22	1/4000	100
14	15	16	17	18	19	20	21	22	23	overexposure	blng red

How to read the table: Look up the aperture in the upper left (e.g., f/5.6, marked in bold), search the measured light value in the corresponding column (e.g., EV 10) and look up shutter speed and ISO in the same row (e.g., 1/30s, ISO 100).

I didn't research much how aperture would be controlled if set to AUTO. But it will choose a combination from the diagonal line of constant EV in the table above. In AUTO, the aperture is controlled live and you can hear the aperture blades moving! IMHO, this is a cool feature for a dSLR with a legacy SLR lens!

(Update) I had another look at this.

In video recording with aperture set to AUTO, I illuminated the sensor with a torch and observed the lens aperture's reaction. This is what happened:

• Without extra light: wide open (f/2.4)
• With medium extra light (torch into lens): shut down (f/5.6) (*)
• With full extra light (torch fully aligned and directly in front of lens): closed down (f/11) (*)

(*) estimated from diameter left open by aperture blades, as seen thru the front lens element.

There are really only these 3 steps. With a f/5.6 lens, this reduces to really only two steps. If it changes aperture, it does so by jumping 2EV, at least. Of course, it causes a visible jump in brightness in the video then being compensated afterwards. Therefore, manually shifting aperture creates a much smoother effect. (end of update)

Note: The above table may not be fully accurate. E.g., the sweet spot shutter speed (1/30s) may be shorter, like 1/50s, actually. Note that many videographers prefer a shutter speed of 1/30s or 1/50s (i.e., the motion blur from it) for 30fps footage to minimize a stuttering effect in panning action. Also note that all this is from my own research. Pentax doesn't disclose the information given above and the recorded video contains no useful meta information.

Now, using the response curve above, you can meter any subject, set the required aperture, use E/V-compensation to hit the required EV value, switch to movie mode (E/V compensation stays active!), lock exposure with AE-L and you successfully manually controlled your video parameters!

It is possible. But I agree that it is awkward in many if not most circumstances. If you need longer shutter times at daylight without wanting to stop down then you need to use a gray filter like you maybe would use for water still photography. Note that for video, you can stop fully down without loosing sharpness in the resulting video.

However, what I did find very easy to use is the following trick: In video mode, before starting to record, I observe the live histogram on the rear display when pointing to different subjects which will emerge during a scene. Then I point to a "typical" histogram and lock exposure. Eventually, I record using these parameters.

Controlling focus

Autofocus stays inactive during recording (it was enabled up to firmware release 0.20). However, it is so slow and badly implemented that it wouldn't be useful in actual footage anyway. If you need to refocus using the autofocus, the fastest would be to set live view autofocus to phase detect and stop a recording (press the shutter again and wait ~2s), press the AF button (~1s) and start recording again (~1s). If there is no time for a ~5s break, then you must control focus manually. Unfortunately, magnifying live view is inactive during recording as well (and the view finder stays dark, of course).

Fortunately, the quality of the rear screen with its 640x480 resolution allows an approximate focus. If the DoF effect isn't required, then shooting with fixed focus at hyperfocal distance is a viable option. The DoF calculations as obtained for an APS-C sensor do still apply. If you need to pixel peep, set circle of confusion to 0.015 mm.

If you need more control over the focus, using either a field monitor or an enlarging eye piece looking at the rear screen may be an option. The K-7 outputs live view and life audio via HDMI in 480p, 576p, 720p or 1080p. The image at the top of this article shows a K-7 hooked up to an HDMI 1.3 type C cable. However, the video data will always be 480p only, possibly enlarged to match the HDMI protocol.

K-7 videographing its own live view from falconeye on Vimeo.

The video above shows how the live feed from the K-7 behaves. In particular, you can assess the latency between reality and HDMI output. I guess it is about 1/3 s.

There are field monitors one can connect via HDMI and mount to the hot shoe or flash bar. The flash bar however, may be the better choice if a microphone is already mounted to the hot shoe ;) Because the feed is always 480p only, there would be no additional benefit in getting a 800x600 or 720p field monitor (this notice may not hold true for the Samsung GX30). A 5-6" 480p field monitor with HDMI input will do it. Avoid monitors with A/V analog input only.

Field monitors may have a headphone jack for audio playback as well.

And of course, for proper framing and smooth operation, you'll definitely want a video rig :)

Controlling shake

The K-7 features electro-mechanical sensor stabilization which proves very efficient in video capture. Note however that it is designed to work for still photography. So, it cannot compensate all the shake during a longer take. Because wide angle requires the anti shake to compensate less and is more stable in the first place, it is best to use wide angle (and tele lenses on a tripod). Or a rig again ;)

Note that a wide angle lens has a closer hyperfocal distance and produces smoother panning as well. So, I just adopted wider lenses as my standard when videographing.

Controlling audio

The built-in mono microphone is very sensitive to environmental noise like wind. So, using an external (stereo) microphone is a much better option (or use external sound recording and a take board). I tried the RØDE Stereo VideoMic connected to the flash hot shoe and it produces excellent results. The recorded quality is definitely more than sufficient for voice and sound. For music one may want to record externally.

Btw, there is no control of volume. But the recording level is relatively low and I didn't have any problems with either oversteer or noise floor.

Now, let's go out and have fun with video. I.e., it is time for part III.

-> Continue to part III