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04-06-2008, 03:31 PM   #1
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K20D and odd white balance problem

I decided to shoot a volleyball game yesterday and convert/save the files in-camera as JPEGs - a change from my past practice of always shooting raw. I'm not sure it was a successful experiment, as I got some odd white balance results, and worse, I have had a devil of a time correcting them.

In this photo, the floor of the gym is too red:



Compare it to this photo, taken with the same camera settings, from the same position (I take up a spot and scarcely move for the whole game), with pretty much the same lighting, and processed with more or less identical settings in Lightroom:



Most of the shots taken during the game look like the latter, with a floor that is more yellow than orange. So what's up with the first shot (and the few others that, like that one, have an orange-ish floor)? I had the camera on Auto White Balance. Is this just what you get when you shoot jpeg? I understand very well that there are dark and light spots in the gym and these affect basic exposure settings, but could a TEENY difference in perspective explain the marked difference in color?

Will

04-06-2008, 03:37 PM   #2
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It may be that there are some fluorescent lights in the area and you're catching it in different parts of the sine curve.

This is why indoor sports suck because of all the mixed ugly light in the room. Also if they are using mercury or sodium bulbs as they get warmer the color changes.

Looks normal to me
04-06-2008, 03:44 PM   #3
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Auto WB can be a finicky beast, prone to substantial shifts when faced with changes in light temperature which our eyes and mind integrate without noticing.

Another factor that may affect your outcomes here is the in-camera JPEG processing. It is downsampling to 8 bit depth and the algorithm has to remap colors from a 12 bit colorspace, so data gets "interpreted" and colors get remapped to approximate values in the smaller 8 bit colorspace.

I'd guess you're seeing the results of the interaction of Auto WB with JPEG downsampling, which could account for the different looks from shot to shot.
04-06-2008, 03:44 PM   #4
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QuoteOriginally posted by codiac2600 Quote
It may be that there are some fluorescent lights in the area and you're catching it in different parts of the sine curve.
Thanks, Chris. My guess wasn't quite as precisely phrased as yours, but I figured it had to be something similar. The only alternative I can think of is, the K20D's white balance is inconsistent, and I'd rather not go THERE.


QuoteQuote:
This is why indoor sports suck because of all the mixed ugly light in the room. Also if they are using mercury or sodium bulbs as they get warmer the color changes.
Well, the main problem I've had in the past has been the lack of light rather than the quality of light. I'm pretty sure there were no windows in this gym, so all of the light was artificial, and it seemed to me to be about equally mixed all over - although the light was more abundant on the other side of the court (when I was shooting to my right).


QuoteQuote:
Looks normal to me
Heh. Well, it doesn't look so normal to me, and I've shot an awful lot of these games now. I am a tad unsure what to think here because two things have changed lately: I'm shooting with a K20D; and I just decided to try shooting jpeg rather than raw. But I suspect that it's the choice of jpeg that mattered here. I'll go back to shooting raw next week. I still get results that are inconsistent initially, but it's easier to fix 'em in post processing.

Thanks,

Will

04-06-2008, 03:57 PM   #5
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QuoteOriginally posted by christinelandon Quote
Auto WB can be a finicky beast, prone to substantial shifts when faced with changes in light temperature which our eyes and mind integrate without noticing.
I do not think that is the problem....
Just toninght I was shooting some scenes (stricltky private, no pics to post) and on the camera LCD I noticed about 3-4 shots with a completely different WB setting, even with manually chosen WB
04-06-2008, 04:01 PM   #6
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I found that the natural mode often gives a more accurate awb than bright mode when shooting under fluorescant lights. Might be just me imagining things again though...
04-06-2008, 04:18 PM   #7
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Next time I would use manual white balance. If that would be off, at least all shots would come out equal and need the same correction.
04-06-2008, 04:42 PM   #8
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As Codiac stated, it is caused by the "flickering" of fluorescent lighting. If you take pictures under these conditions with the K20D in burst mode, you'll be able to see all the color shifting that happens under fluo. You would get the same results with the Canikon pros with their high fps rate.
That's why it is better to shoot RAW under these conditions so you can correct WB in post. There is a similar post on
www.pentaxuser.co.uk
Just give it a look for more detail. You can also check fluorescent light on Wikipedia for a more detailed explanation.

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