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Forum: Pentax DSLR Discussion
04-09-2007, 12:02 PM
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Hi Jonas,
I believe that all K10Ds have VPN to a very similar level, given the exact same image capture circumstances. Of course, getting the same exact exposure and color temperature on two different cameras at two different times is impossible.
I also believe that seeing it or not seeing it is influenced by the following (at least):
Monitors being used.
Ambient viewing conditions.
Presence of any color blindness (I have a bit of red/green color blindness, which is reasonably common).
Pattern recognition differences in different people.
Here is a test that I believe will show very similar VPN in all K10Ds:
Create a new image in your favorite editor. In a white (255,255, 255) background, place two squares, one filled with 128,128,128, the other filled with 000,000,000.
Leave plenty of white area around the squares.
Print the image on a good quality B&W inkjet on matte paper.
Tape the print down and light it as evenly as you can.
Set the K10D to ISO 1600 and perform a custom color balance on the white area in the print. Spot meter on the white area and adjust the exposure until you see that the histogram is just under clipping on the right side.
Shoot a RAW image.
Open in your favorite developer, leaving all settings "as shot". Use the little eyedropper to make sure your white is just under 255.
The black square will have some noticeable patterning in the vertical direction, albeit reasonably faint.
Now push the exposure just +1 and the patterning will be much more noticeable in the black square. I never saw any pattern in the grey square no matter how much it was pushed. Note also that your black square is no longer black. Herein lies much of the controversy:
If a part of my exposure is 000,000,000 why would I push it such that it is no longer black?
On the other hand, I am sure that patterning shows up somewhat before full black as I have tested with shots of my white wall where some detail was still visible and pushing +1 started to reveal distinct green and purple patterns. +2 and the patterns were very obvious. The wall was exposed to be very dark, maybe zone 1 or 2, but not black.
So, the absolute amount of illumination that hits the sensor is the main driver of VPN, but it seems to follow light and color gradients in these dark areas as well (which is a function of the image prcessing done by the NuCore chip). This is why it is usually seen in smooth background areas, usually darker, many of which might have also had a color temperature gradient as well. High ISO is not really the cause in the normal noise amplification sense, rather low light levels in certain parts of the scene where the NuCore performs certain tricks to compensate for color and light gradients, and also where a dark level offset error will show is the cause. Unfortunately, it seems to do this in hardware so we cannot get at the unprocessed RAW data to apply a different technique that might work better.
Normally, I have no desire to shoot any 10MP APS-C camera at 800-1600 ISO, and even less desire to push that shot +1 or more, so I have not seen VPN in any but test images, but there is no doubt in my mind that every K10D camera will produce pattern noise under certain conditions.
Ray
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Forum: Pentax DSLR Discussion
04-06-2007, 06:33 PM
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I guess we have differing definitions of low key and that may be the problem. Low key, as I understand it, means predominantly similar tones, mainly darker, with few, if any, highlights. High key is just the opposite.
Google Low key definition and you will find any number of definitions that pretty much match this definition.
I also have several photographic texts with the same or similar definition.
What is clear is that play between sun and shade is most definitely NOT low key and is beside the point I was making altogether.
Moody shots also do not have to be crammed into the last 3 stops of DR at the low end of the sensor range to be moody and dark at the final result.
Sparkling sunshine is also not germane to the issue of shooting low key images as far to the right on the exposure histogram as possible in order to avoid excessive noise.
I do not know about you, but when faced with less than sparkling sunshine, in many cases I can simply use a slower shutter speed or a wider aperture. This is not always possible (like with action shots), but there is nothing new about that in the world of photography.
The bottom line is that one can often expose to use as much of the full DR as possible so to avoid noise issues. If you leave 2 stops of room under the right side of the histogram when exposing your low key image, you are simply limiting your DR and inviting noise problems. Many, if not most, of the "VPN" images I have seen posted are muddy, seriously underexposed scenes shot at high ISO and pushed significantly.
If you have VPN problems at 100ISO, you should send the camera to Pentax with sample images and ask for a repair or replacement. People that claim to have such problems and choose not to send the camera back puzzle me. I guess as far as I am concerned there is a growing credibility gap when these folks continue to hammer on how bad VPN is with the K10D but refuse to make a warranty claim.
As for VPN at 100 ISO in my images, I have yet to see that in either of my K10D bodies. I can see VPN in deep shadows (maybe zone 1 or perhaps 2) at ISO 1600 in areas with little detail, more so if I push the image more than one stop.
While I believe that all K10D's behave this way, perhaps some worse than others, this is not an issue for me as I never expected a 10mp APS-C camera to be usable at high ISO. I reach for my K100 for those shots.
Ray
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Forum: Pentax DSLR Discussion
04-05-2007, 09:24 PM
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"No camera can handle 6 f stops under exposure but a camera should be able to handle the needs of low key imaging. "
I have read this "low key" argument with relation to VPN and the K10D several times now, and it seems to me to suggest a fundamental misunderstanding of how to best use the available DR of your camera.
Just because the image consists mostly of tones that are within a limited brightness range, and in the case of "low key" obviously darker tones, does not mean that you have to expose such that they all fall into the "mud" at the low end of the sensor's range.
In fact, exposing this way with any digital SLR just about guarantees that you will have considerable noise in the image, especially at higher ISO settings.
It makes more sense to move the exposure to the right to get more light onto the sensor to get your image into the region where the sensor signal to noise ratio is much better.
You can then adjust the overall levels down in PP to any level you desire, giving you the darker overall "low key" look you want without extra noise.
Of course, I am assuming that "low key" is defined as I described above and that the entire DR of the scene being captured fits well within the DR of the camera, leaving room at the upper end to add exposure without clipping.
So, just because the image is low key does not mean that you have to cram all of image into the bottom 2 - 4 stops of the sensor range. Given this, I fail to see where "low key" shots with the K10D will necessarily have to result in VPN, or that "low key" shots are necessarily limited by the K10D and VPN.
Ray
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