18% Grey card verses white card WB test

[JZaun]

Thanks for all the input on my grey / white card question. I decided I had to run a test and compare WB using AUTO, 18% grey card and White card, (Office max printer paper). I Used the 20D on tripod with 2, 100 watt reflector lights. NO post processing except size for the web. I did try post processing with PSE3 and could make all 3 look the same :?



Auto WB
http://www.bytegallery.com/data/3222/51Auto_WB-med.jpg

Custom WB using 18% grey card
http://www.bytegallery.com/data/3222/51Custom-_18_grey_paper-med.jpg

Custom WB using white paper
http://www.bytegallery.com/data/3222/51Custom-_white_paper-med.jpg

At least in this test the grey and white worked the same. Auto was the worst.

JZ

[Jon]

I can see a difference between the white paper and the grey card. I just wish I could be sure that it's better colour balance in the grey card, not the knowledge that it was the grey card that makes me prefer the one using the grey card.

[Motorsports Photo]

AFAIK-

grey card is for exposure

white is for color balance.

Of course you can tweak anything in photoshop to match, its just easier when the you take it right to begin with.

-Pete

[Jon]

It doesn't matter what reflectance your custom white balance target has - you can over/underexpose to make it white, or let the auto-exposure fall out as neutral grey. What's critical for this is that the target actually be colour-neutral, so the adjustment will not be biased. A standard 18% (Kodak's, anyway) grey card is colour neutral.

[roanjohn]

I prefer the grey card............but its really tough to tell the difference.

Ro1

[RDKirk]

A true white card is color neutral; a true gray card is color neutral. To the camera, a white card is nothing but a gray card that must be under bright light.

A gray card is more versatile--it's easier to use for both exposure and color balance because it's not already at the edge of the envelope for exposure.

A number of people have run tests that indicate that even for color balance, cameras are more accurate with some shade of gray than with white. This includes tests with accurate materials like the MacBeth Color Checker. Again, it's probably a matter of the camera operating more in the center of its range than an extreme.

"Plain" white is almost never "plain." It often contains UV-activated brighteners than can appear considerably cooler to the camera, especially under flash. The white side of a Kodak gray card should be free of brighteners--but maybe not. The Kodak card was not actually designed for color balancing; some people report that the Kodak card's gray side doesn't respond properly in all kinds of lighting for color balance. However, if you include a Kodak gray card in the scene to determine color balance during editing, it's perfectly suitable.

[Niloc Yarts]

I have found that the Kodak grey card reflects stong sunlight which makes it appear less grey then it should be.This causes underexposure and is not all that helpful. Any comments?

[Wilt]

I have found that the Kodak grey card reflects stong sunlight which makes it appear less grey then it should be.This causes underexposure and is not all that helpful. Any comments?

Are you referring to surface sheen which can fool a reflected light meter into underexposure?...Yes, it can happen with the Kodak grey card (and other grey cards). That's why you see warnings about angling the card to not reflect extra light back to the meter.

[Niloc Yarts]

Thanks, yes, but by how much do you know to angle the card?

[Wilt]

Look at the card with the naked eye as you alter its angle (tip slightly toward/away, angle slightly toward/away) and you can SEE the sheen if it is occurring. (It will not occur in all conditions...imagine you're holding a mirror, would you see the sun (o other very bright source) in it? If so, that is the angle of sheen!

Using a meter, notice if there is a peak reading as you change angle, vs. a fairly constant reading at all the other angles...the peak is showing the effect of the sheen

[Niloc Yarts]

Thanks very much for your help- I shall try it!