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11-18-2017, 10:14 AM   #1
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Magenta color cast while using AWB

I shoot raw files so no problem making corrections. I have noticed on several occasions that when shooting subjects with a fair amount of red, (red barn door in bkgrd) on even in these new baby photos that I get a color cast which can change from one image to the next under exactly the same lighting conditions. Any ideas how or why?

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11-18-2017, 10:23 AM   #2
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The AWB function takes the overall tint of the image. AWB works best on scenics, in my opinion. You can fix this tint easily in post, or use a grey card and set the white balance before taking the photos.
11-18-2017, 10:32 AM   #3
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Could be related to the light source especially if it is not a continuous light source. The best is to shoot a manual white balance with WB card, something we know is white or a piece of white cardboard, is not the best but can work, then use that white balance setting for other photographs taken under the same lighting.

---------- Post added 18-11-17 at 18:44 ----------

Haven't seen that much bias with my K1.
Could also be a problem with the camera itself, or camera settings, or firmware version.

- Firmware: What firmware version is installed?
- WB settings: for each WB setting, there is an additional tweak possible, this setting is also done for the WB Auto setting. It could have been modified different from factory settings and not reset.
11-18-2017, 10:57 AM   #4
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A second thought: if the lighting is fluorescent, "interesting" things happen with colours.

11-18-2017, 11:23 AM   #5
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Thanks for the input. These were both window light within seconds of each other. No change in light or quality of light. I have only noticed this when shooting with a large amount of red in the image. What is strange to me 1 image is correct and the next taken after a second has the WB messed up. Very strange indeed. Of course, I shoot raw so I can correct in post processing just wondering why such a dramatic response between images.??
11-18-2017, 11:36 AM   #6
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There are several things which changed in the background including that pink bow shaped object in the upper right of the first shot. Depending on your camera, these things could have accounted for the change as described in previous posts. It won't take much to affect the auto white balance in some cases, although having a particular color in an image will tend to reduce that color whereas in your case it appears to have increased it. Again, it depends on the algorithm that the camera uses for AWB.

Manual WB overcomes this problem but be sure to use a neutral card placed in the same light as the subject.

As an aside, a nice trick if you want to tint an image, is to manually white balance on a tinted card (there are cards made for the purpose). This will introduce a tint of the opposite value in the photo so balanced. It can take the place of a lens filter for minor adjustments if done properly. Then again, there's post processing - yay!
11-18-2017, 12:14 PM   #7
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Thanks, for the input as well. I understand the WB issues and never worry about final color balance as I shoot raw and correct as needed. I am new to Pentax and the K1 and to be honest have never seen this with my Nikon gear after shooting weddings for 20 years. I am talking about 2 images 1 sec apart having two different color casts. My samples are just screen captures but the images are identical. I have seen this in my outdoor portrait sessions as well, but only against a red background, like a barn door. It seems that the red throws off the AWB. Just have not seen this in any of my other cameras, just questioning if noticed by anyone else.

I understand how to manage this just wanted to see if anyone else has noticed this as well?
11-18-2017, 12:51 PM   #8
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I have encountered somewhat similar problem with red colors. When subject has single red color it can be managed at PP stage, but when there are various shades of reds, output comes out as blob of red. Very poor resolution within red shades. I have seen this problem consistently when photographing acrylic paintings. I keep a gray card within the frame and use it for both metering and WB adjusting at PP stage. In spite of all this i used to get red blobs. This was my experience with K3 and yet to try using K1.

The red shades that I photographed are complex than autumn leaf. This was created by stacking 10+ layers of different shades transparent reds, oranges. When light falls on that patch of painting, these color get mixed up and that is a beauty to see. I think this technique is called as visual-color mixing.

11-18-2017, 02:59 PM   #9
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QuoteOriginally posted by pentaxfall Quote
I have encountered somewhat similar problem with red colors. When subject has single red color it can be managed at PP stage, but when there are various shades of reds, output comes out as blob of red. Very poor resolution within red shades. I have seen this problem consistently when photographing acrylic paintings. I keep a gray card within the frame and use it for both metering and WB adjusting at PP stage. In spite of all this i used to get red blobs. This was my experience with K3 and yet to try using K1.

The red shades that I photographed are complex than autumn leaf. This was created by stacking 10+ layers of different shades transparent reds, oranges. When light falls on that patch of painting, these color get mixed up and that is a beauty to see. I think this technique is called as visual-color mixing.

This is interesting as on a different shoot outdoors with red barn door I did get this effect. ! photo spot on the next not so.
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11-18-2017, 03:12 PM   #10
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QuoteOriginally posted by StanT Quote
This is interesting as on a different shoot outdoors with red barn door I did get this effect. ! photo spot on the next not so.
I always thought white balance settings only affected JPG and not RAW. Now I have learned something because of your misfortune. I hope the issue gets resolved.
11-18-2017, 03:31 PM   #11
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It would be useful so see the EXIF data of those images. Screen shots as provided don't help troubleshoot the problem. There are many image processing settings on the K-1. One or more could accidentally have been turned on.
11-18-2017, 04:52 PM   #12
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Thanks, one would think so, but the images are 1 after the other so if there was a setting issue it would be consistent. The DNG files look just like this. even 10 sec apart two different colors cast 1 normal 1 magenta.
11-18-2017, 05:30 PM   #13
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If that is reproducable it should be worh a bug report. There is a thread somewhere for bugs and feedback.
11-18-2017, 05:55 PM   #14
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QuoteOriginally posted by StanT Quote
Thanks, one would think so, but the images are 1 after the other so if there was a setting issue it would be consistent. The DNG files look just like this. even 10 sec apart two different colors cast 1 normal 1 magenta.
I read that DNG file stores processed a JPEG image and also raw-image. Many image viewers show the processed JPEG (embedded inside DNG) instead of rebuilding the image out of raw-data. This is for s/w optimization. So try generating JPEG from DNG, see if that JPEG is any good.

DNG file format is able to store multiple images. Here is an another example. In case of in-camera HDR the final DNG will be a large file, and it will have the raw files used for HDR. DCU5 tool is able to extract the original raw files. In fact this feature of DCU5 saved the day for me.
11-18-2017, 06:05 PM   #15
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Just wondering out loud: is there a white balance bracket feature on the K-1?
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