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09-24-2009, 04:27 AM   #1
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K-7 Auto White Balance problem

In an other thread on this forum, we have discussed the K-7 auto white balance performance.
Although it works great in many environments, I would like to warn people who only shoot in JPG when working in "yellow" environments.

Applying post processing clearly solves the problem.

Examples:

K-7 in Auto White Balance, shot in RAW:



Now, the same image, processed in Lightroom 2.5, WB set to daylight:



At first I thought my K-7 was broken, since almost all pictures suffer from this blue instead of black shadows.
Fixing the JPG's that I shot does not completly turn the shadows blue into black, and also the fixing affects the other colours in the images too much.

My guess is that Pentax has listened too much to the camera critics, trying to improve their auto white balance performance in artificial (yellow) light.
The effect is that in outdoor situations, you will have a blue cast over all shadows in many of your pictures.

Therefore:
- For RAW shooters: easy to repair.
- For JPG shooters: be warned, don't trust Auto White Balance too much.

- Bert

09-24-2009, 05:30 AM   #2
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Good tip.
Thanks for sharing it Bert.
Does look like an overcorrection.
A good reason to shoot RAW, no matter the camera.
09-24-2009, 06:31 AM   #3
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I don't really rate it a "problem" as such....you just need to know the limits of some of the cameras settings, and know that there are other ways around it.

My WB setting for the K-7 is In very bright daylight is Daylight WB.
In just about all other situations AWB works fine.
Does that sound logical ?
09-24-2009, 01:17 PM   #4
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thats more of a coverter issue than a real wb one, the K7's awb was rather good, tho it sided with warm in sunlight vs accurate.

09-24-2009, 04:21 PM   #5
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I would suggest that your AWB is broken and/or as Torphoto suggests, the converter could be bad at k-7 files... I've shot about 4000 frames w/ my K-7, and tungsten or daylight, the AWB is almost always right on - I've never seen a blue cast like you've got there.
09-25-2009, 04:04 AM   #6
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Open shade situation

This particular shot is "open shade" situation and very tricky to get accurate WB. I agree with you that AWB of K-7 has been fooled here. It would be interesting to check what color temperature it read in the original shot. Can you check it in ACR? and also let us know the temperature for the corrected one.

I agree with Ash, the RAW is proving its usefulness in such cases. Have you tried any shot with daylight WB (in camera) during your safari trip?

Atindra
09-25-2009, 07:22 AM   #7
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Just a thought inspired by Atindra's post - is it possible, that instead of auto, your camera's WB was set to Tungsten or similar? There's a "White Balance" tag in exif that will say "auto" if it was shot in auto mode - you can read all exif tags with PhotoMe or exiftool.

Edit: Ok, I should have checked first... You're photo has exif intact and does show "auto"... oh well, just a thought.
09-25-2009, 08:33 AM   #8
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QuoteOriginally posted by heliphoto Quote
Just a thought inspired by Atindra's post - is it possible, that instead of auto, your camera's WB was set to Tungsten or similar? There's a "White Balance" tag in exif that will say "auto" if it was shot in auto mode - you can read all exif tags with PhotoMe or exiftool.

Edit: Ok, I should have checked first... You're photo has exif intact and does show "auto"... oh well, just a thought.
Ok, to clear up things:

1) I did not use a TC with this photo.
2) Lightroom indicates that the colour temperature "As Shot" = 4300, Lightroom Daylight = 5500, I guess temperature representing the reality best is ~ 4900.
3) PhotoMe tells me that AWB is not set. I cannot find the field representing the 4300. Tell me specifically which fields you'd want to see.

This is NOT a 1 image issue. I can show you plenty.
I have been shooting with a K10D and a K-7 side-by-side. Only the K-7 shows the blue casts.
The K-7 AWB has been fooled, the K10D's not.
All K-7 images with the blue cast are daylight shots (in sun light), where AWB set the colour temperature between 4200 and 4300.
I agree with Falconeye that 5500 K is too much. Refering to what my K10D makes out of it, 4800K - 4950K would have been much closer to reality.

Here, at home, the K-7 AWB does very well. However, remember that the world there is predominatly yellow by colour and here it is not.

- Bert

09-25-2009, 09:19 AM   #9
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What is your setting for Custom Menu Item 12 ? AWB in Tungsten Light - Subtle (Default) or Strong ?

If you set it to "Strong" it will apply strong correction to any scene it interpretes as Tungsten light , which it may well have in the African savanna.
09-25-2009, 09:23 AM   #10
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Dumb response ;)

Since the K7 has a "tungsten" wb adjust is it possibe that this may be affecting the AWB? Not familiar w/ the camera but some tweaking of the tungsten AWB may be in order..................
As far as I can tell there are no other reports of this issue...opp's found this.
so I may be on to something here:
Re: K7 & K20D AWB Difference.: Pentax SLR Talk Forum: Digital Photography Review
GordonBGood wrote:

Pete Fang wrote:

Thanks for the test. My own experience is also that the K-7's AWB works much better under artificial light sources. I briefly tested the K-m and its AWB was an improvement over the K20D but the K-7 seems to be even more consistent.

Pete, however, the cost of getting less yellow AWB in tungsten light seems to be a slight tendency to "bluer" AWB in more natural daylight lightening as reported by many comparing images to the K20D. This is a natural consequence of increasing the colour temperature range for AWB.

This bluer look for the K7 accords with my experience. I am now occasionally taking out blue in PP with K7 files, especially in naturally lit pictures. How can I tweak the AWB in camera as to warm it up a bit?

Adam, some have been finding that the Fine Tuning option for Auto White Balance (AWB) has done the trick, with a setting of about one or two toward the red and maybe a one toward the green (if you like a slightly yellow look). This will likely also affect the AWB with tungsten lighting, but perhaps this in conjunction with the stronger Tungsten compensation as selected in the Custom menus?
On a personal note this appears to be a software "glitch" in processing the RAW file. guess that's a bit self evident though
It would be helpful to know if you have changed the "tungsten" wb adjustment.

Last edited by jeffkrol; 09-25-2009 at 09:45 AM.
09-25-2009, 09:28 AM   #11
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QuoteOriginally posted by bymy141 Quote
Ok, to clear up things:

1) I did not use a TC with this photo.
Unless I missed something, I don't think anone suggested otherwise. When people said it might be a converter issue, I would assume they meant a *RAW converter* issue, not a *teleconverter* issue. the implication presumably being that another RAW converter might render the image less "cold". I kind of doubt that, though, based on the temperature numbers you posted.

Anyhow, what cracks me up (sort of) about this is that it appears the K-7 has done exactly what people have been begging camera manufacturers to do for years - to make the AWB aggressive enough to completely remove a color cast from yellow/orange lighting. That's what people say they want when shooting indoors in tungsten lighting, anyhow. But then when the camera does the same thing outdoors - removing the yellow/orange cast from the sunlit areas, thus leaving the color flat and the shadows blue - they are not happy.

QuoteQuote:
3) PhotoMe tells me that AWB is not set. I cannot find the field representing the 4300. Tell me specifically which fields you'd want to see.
I think WB is not stored as a single number, but a whole complicated slew of numbers representing the intensity of the light at different wavelengths, from which a RAW converter calculates a WB value. At least, I've heard that's the case for DNG; perhaps PEF has a single field somewhere in an undocumented makernotes field or something.

QuoteQuote:
The K-7 AWB has been fooled, the K10D's not.
I'd suggest it's the other way around, depending on what you mean by "fooled". The K-7, as mentioned above, appears to have done exactly what people have been begging cameras to do under tungsten light for years.

Last edited by Marc Sabatella; 09-26-2009 at 11:02 AM.
09-25-2009, 10:21 PM   #12
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Getting interesting

Thread is really getting interesting and informative. We should thank OP for bringing out this point of AWB getting fooled in certain conditions.

I dont think the special correction for Tungsten light on K-7 is being applied or affecting the AWB, because if thats the case then we would see very poorly white balanced shot from this camera in many situation, but that is not the case. In fact K-7 has really very accurate AWB in most conditions, I could gather from the shots so far I have seen (here, on DPR and on Flickr which makes about thousands of shots).

This particular Savannah condition with inclined sunlight and glowing golden-yellow grass, I guess is creating a color temp similar to tungsten source and camera kicks in the correction for it leading towards blue bias.
And as per OP (Bert) this happened with many of his K-7 shots, therefore its a reproducible phenomenon on his camera.
I suggest the following

1. Better to use "Daylight" or custom corrected WB in this situation.
2. Shooting RAW is easy way out because shooter need not to worry about WB while in the field like this.

Atindra
09-25-2009, 10:33 PM   #13
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i use custom corrected 99% of the time, but sometimes daylight when its not normal daylight (eg flourescent lighting) looks more natural
09-26-2009, 02:55 AM   #14
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QuoteOriginally posted by kittykat46 Quote
What is your setting for Custom Menu Item 12 ? AWB in Tungsten Light - Subtle (Default) or Strong ?

If you set it to "Strong" it will apply strong correction to any scene it interpretes as Tungsten light , which it may well have in the African savanna.
No, it is on default: 1 (Subtiele correctie, in Dutch)
09-26-2009, 03:00 AM   #15
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QuoteOriginally posted by Atindra Quote
Thread is really getting interesting and informative. We should thank OP for bringing out this point of AWB getting fooled in certain conditions.

I dont think the special correction for Tungsten light on K-7 is being applied or affecting the AWB, because if thats the case then we would see very poorly white balanced shot from this camera in many situation, but that is not the case. In fact K-7 has really very accurate AWB in most conditions, I could gather from the shots so far I have seen (here, on DPR and on Flickr which makes about thousands of shots).

This particular Savannah condition with inclined sunlight and glowing golden-yellow grass, I guess is creating a color temp similar to tungsten source and camera kicks in the correction for it leading towards blue bias.
And as per OP (Bert) this happened with many of his K-7 shots, therefore its a reproducible phenomenon on his camera.
I suggest the following

1. Better to use "Daylight" or custom corrected WB in this situation.
2. Shooting RAW is easy way out because shooter need not to worry about WB while in the field like this.

Atindra
I agree.

These suggestions are the same as I suggested in the other thread, discussing my K-7 experiences.

- Bert
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