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Old Jan 5, 2004, 11:31 AM   #11
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Ok thanks again and a lot for many quick answers!

It all sums up in me doing as I begun, using a grey card and setting a custom/manual white balance under the lighting conditions I work under.

But something strange really has happened with the test shots I made. They should give the same or very close rgb-values since I made a custom white balance (one for each ligthing condition) and directly after that shot my test images.

I will try a new test...

/Samuel
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Old Jan 5, 2004, 3:28 PM   #12
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Are you sure that the second picture used the custom white balance. If you turned your camera off between pictures, it may have reverted to the auto white balance. Can you check the metadata on the images to see what the white balance setting was?
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Old Jan 5, 2004, 4:48 PM   #13
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There is more of a difference between daylight and florecent than just color temperature. Daylight has mainly a smooth black body distribution while florecent has a very spikey distribution.

Try the same experiment with daylight and tungsten lighting. Also at different times of the day and with different cloud covers. If those match fairly well with manual white balance, the issue is the "spikeyness" of the florecent lighting.
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Old Jan 5, 2004, 5:34 PM   #14
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Well, here I am again. Now Ive repeated my test, and the results are here:

http://www.bildtre.com/samuel/test/

There is a little but noticable difference in the color cast in these shots. And I was expecting/hoping that the would be matching. Am i hoping to much? Is it possible to get closer than this?

This is what I did:

- Lit a lightbulb in a dark room.
- Measured the exposure manually by filling up the viewfinder with it.
- Made a custom whitebalance by filling up the viewfinder with the greycard.
- Took a picture of the greycard against a white wall (in the same place as it was before), this resulted in the picture "bulb.jpg". I used the same exposure settings as when I did the white balance.

Then I did the same thing again, but with a fluorescent as a light source, which resulted in "fluor.jpg".

/Samuel (who used an Fujifilm S2 for shooting)
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Old Jan 5, 2004, 5:47 PM   #15
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Were you expecting the bulb.jpg and the flour.jpg to be the same?

I'm not sure I follow what you're trying to accomplish, I guess.
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Old Jan 5, 2004, 8:34 PM   #16
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I have a Canon G3 and I just keep a sheet of plain white paper with me. If the lighting is tricky with odd colour casts (snow!) then I just pull out the piece of white paper and set my white balance to the piece of paper. So far it's worked great, I get perfect whites with no colour casts.
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Old Jan 6, 2004, 11:07 AM   #17
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First off, to set white balance, shouldn't you use a white card, not a grey? That is what it says in my 10D manual (I made this mistake in the past, and was corrected here.) A grey card is used for proper exposure, isn't it?

Another thought, just something that poped into my head (I'm fairly ignorant here.) Do either of the types of lights alter their light quality when they heat up over time? Could that have effected anything.

Also, don't floresent lights pulse/flicker slightly? Itsn't it something like 60hz or something? If the picture was taken at different parts of the cycle could that effect the results?

Just some thoughts that poped into my head....

Eric

ps. Is it just me, or do both pictures how uneven lighting? The bottoms seem a bit darker than the tops. You've gotta fix your lighting arrangement too.
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Old Jan 6, 2004, 4:19 PM   #18
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.............Also, don't floresent lights pulse/flicker slightly? Itsn't it something like 60hz or something? If the picture was taken at different parts of the cycle could that effect the results?...........

That's precisely one of the problems. Digital cameras are sampling devices - they timeshare all the things they do through their microprocessor. I've even seen auto exposure come out wrong under discharge lighting. Take 5 shots, look at the Exif and I'll bet the exposure will differ. Movie cams can have similar problems when their frame exposure rates run closely synchronised to flourescents, electronic shutter can interfere as well.

However, I think the first post said incandescent, which I'd take to mean tungsten. In wavelength and camera sensitivity terms there's a lot of difference between flash/daylight and tungsten so it would't surprise me if an auto balance under tungsten where the camera will be stretching its gain, might be different to more lumens from daylight. So I wonder if the exposures were different in the tests 'cos I've found auto balance for tungsten indoors so poor (due to low light) that I always use the preset. On the flourescent issue, don't forget they may look bright, but actually there's not a lot of light lumens there for digicams unless you're talking the proper daylight matched cold light type, used for TV studio.

So my guess is the auto white balance will not track correctly when the light levels are low, compared to daylight. It's sort of the autofocus analogy only it's white bal. VOX
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