Canon Rebel XTi, Custom WB

[IvorE]

I just recently got a Canon Rebel XTi and am having trouble setting the custom WB. In the menu, I scroll down to Custom WB, press "Set" and get the last shot I took (a picture of a white sheet of paper), and I press "Set" again. sometimes it works but a lot of the time, it doesn't seem to take--if I shoot the white paper again, it still looks dirty grey. What am I doing wrong? I don't get the set screen/import image that they show in the manual--well I did once, but don't know how I got to it!

Thanks for the help.

 

[Mike Teezie]

I can't help with your main issue, as I don't have an XTi to fiddle with - but I can tell you this - if you are using a custom WB, you should look into getting an 18% grey card. They are really cheap from Amazon or B&H.

 

[beavo451]

If you take a picture of a just a white sheet of paper, the resulting picture with show up as grey. The white fools the camera meter into thinking it is overexposed, so the camera acutally underexposes the white. That is why your pictures of the white paper are coming out grey, even though you may have set the white balance correctly.

 

[IvorE]

Should I use grey card for WB?

I do have a grey card--I've been metering off it for manual exposure. Should I take a picture of the grey card, instead of the white sheet of paper for setting the WB??? If the camera is underexposing the white sheet, is it getting a true reading to set the white balance?


thanks for the help.

 

[Damitri]

You can use a grey card or a white paper to set the WB. All it does is setting the color balance so that you get neutral white or grey (no yellow or blue cast). It is basically unrelated to exposure which determines if your white paper comes out white, grey or almost black.

It is better to use an 18% grey card because they are guranteed to be neutral in color. With just a "white" paper you never really know (if you are a perfectionist!). With an 18% grey card you also set the WB at a correct exposure. I am not sure but that may make it more exact depending on your camera.

So: WB only removes color casts. It does nothing to exposure (how dark or bright the resulting image is)

Godd luck!

 

[ChrisA]

... it still looks dirty grey.

"grey" is what you want. What you are trying to do with white balance is remove any red or blue tint. You want a perfect 18 percent grey.

Auto exposure systems are really stupid all they see is the amount of light and set the exposure such that on average the frame is light grey. In theory you wuld get the same result if yu shot a black papaer in full automatic as a white paper. Grey in either case. Some modern meters are slightly smarter but a blank sheet of paper can fool even a Nikon RGB meter.

It will be real hard to know if you got WB perfect ntill you go indoors and look in the computer screen. The screen on your camera is in the same light as the paper and your eyes automatically adjust to the light, so to your eyes white is white, looking is not a good test.

 

[IvorE]

Thanks

Thanks so much to all of you. Your advice really helped. I set the WB using an 18% Grey Card and got the best colors so far with this camera! I think using that neutral grey made a big difference.

Also, perhaps switching to Adobe RGB color space may have had something to do with it. Anyone know what impact that might have??

 

[beavo451]

Also, perhaps switching to Adobe RGB color space may have had something to do with it. Anyone know what impact that might have??

Aboslutely nothing.

Well... maybe you can see more shades of gray.