What's the difference between a white card and gray card?

[Theantiquetiger]

I don't understand why you would set your WB to a gray card. Is this to make for a different feel to the image?

 

[480sparky38 37]

What's the difference between a white card and gray card?

A white card may be 255:255:255 in the image, so there's no data the software can use to change WB with.

I don't understand why you would set your WB to a gray card. Is this to make for a different feel to the image?

A gray card is a known color. Using it allows you to adjust all the other colors in the image so they are rendered as accurate as possible.

 

[greybeard32 4]

White balance is a misleading term, kind of like "depth of field". A better term would be light balance. A good gray card will let you nail the color balance in your photo, a pure white card can do the same thing but, pure white is often hard to find so I stick with gray. Oh, "depth of field" should be "depth of focus"..........lol

 

[EIngerson]

Actually, both will work. The issue is, grey will put you in the middle of the color spectrum. White will put you at the bright end and black will put you at the dark end. Now, before anyone flips out. Colors are still a reflection of light. That's why I speak in terms of color and not light. Sometimes its easier to connect to it.

 

[runnah]

Actually, both will work. The issue is, grey will put you in the middle of the color spectrum. White will put you at the bright end and black will put you at the dark end. Now, before anyone flips out. Colors are still a reflection of light. That's why I speak in terms of color and not light. Sometimes its easier to connect to it.

I don't think it's that black and white.

 

[KmH]

A good gray card will let you nail the color balance in your photo

Only if light having only 1 color temperature was used to make the photo. If mixed lighting (more than 1 color temperature) is used color balance cannot be 'nailed'.

The key part of a gray card is that each of the 3 additive colors DSLR cameras use have the same value.
Gray is preferred because the camera's light meter is calibrated based on the assumption that most scenes average out to middle gray that has a 12% to 18% reflectance.
White/Black has a much greater/lesser reflectance and can fool the camera's light meter.

The better gray cards are not only made to be neutral gray, they are also made to have that 12% to 18% reflectance.

Human eyes are not accurate enough to see that most of the things that look white usually have a slight color cast.

 

[EIngerson]

I don't think it's that black and white.

Believe me I know. Lol

 

[pixmedic]

Actually, both will work. The issue is, grey will put you in the middle of the color spectrum. White will put you at the bright end and black will put you at the dark end. Now, before anyone flips out. Colors are still a reflection of light. That's why I speak in terms of color and not light. Sometimes its easier to connect to it.

I don't think it's that black and white.

its really more of a grey area.

 

[480sparky38 37]

Actually, both will work. The issue is, grey will put you in the middle of the color spectrum. White will put you at the bright end and black will put you at the dark end. Now, before anyone flips out. Colors are still a reflection of light. That's why I speak in terms of color and not light. Sometimes its easier to connect to it.

I don't think it's that black and white.

its really more of a grey area.

Grey area........ or gray area?

 

[runnah]

Grey area........ or gray area?

A for America, e for Europe.

 

[Derrel]

Grey area........ or gray area?

A for America, e for Europe.

The Canuckians also use an "e" in their gray colour, as in their crazy Canuckian football's championship game, the Grey Cup.

News - grey cup,100gc | CFL.ca | Official Site of the Canadian Football League

 

[WayneF]

I don't understand why you would set your WB to a gray card. Is this to make for a different feel to the image?

No. Either white or gray can work, but the WB idea is a neutral color (but not too dark is a good idea too). Pure gray is a neutral color, not red, not blue, i.e., no color cast (but random grays certainly can have a color cast too - there are pink grays and blue grays, etc). Neutral gray has equal RGB components, like RGB (50,50,50) or RGB(150,150,150) are neutral gray. White and black are just special cases of a gray tone, black near RGB(0,0,0) and white near RGB(255,255,255). This shade that we see in our picture depends entirely on how much we light it, but the neutrality should remain.

Except the color of light varies. Incandescent is orange, skylight is more blue. Different instances of any of them vary, flash varies color with power level. This non-neutrality gives a color cast to all subjects in that light.

Our white balance tools (today's variety) watch us click on a neutral spot in the picture (a white card or gray card). That is how we tell the computer that "this spot is neutral, make it be neutral". And it does, it removes any color cast there, and leaves it neutral (equal RGB). Which we know it should be... so that ideally corrects the whole image perfectly.

Even black can work, but a dark color like RGB(40,40,40) is too near zero to ever be able to show much of a red cast. It can sort of work if no other choices, but lighter, towards white, is the best bet, shows the color cast better.
Gray cards for white balance are nowhere near as dark as 18% (and 18% cards are not color controlled anyway). Still though, better than nothing. Even scene stuff we find in the picture can work, white plates, envelopes, church steeples, picket fences, shirt collars... maybe not precise, but all normally much better than nothing. But a good known white card is best.
One example of this variety is at White Balance Correction, with or without Raw

One consideration of white is we cannot let it be clipped at 255, because if one channel is clipped, we lose our color cast, so there is no clue how to correct it.
But a white card in a portrait scene probably does not reach 200, because we cannot light humans that bright either.
My notion is the white card is about perfect. No gray pigments for manufacturing to have to control either. I have a couple of WhiBal cards, but I prefer to use the Porta Brace White Balance card ($5 at B&H).

 

[Biota]

I understand what is written above, and i used a grey card as well. But I dont fully understand why shades are used over colors for setting the balance? Is it because the sensors work in the 3 color system and the shades are "neutral" to all of them? I dont think i am wording it right...

 

[darkchild]

I just read this whole thread and my unconfused mind suddenly became confused.

 

[WayneF]

I understand what is written above, and i used a grey card as well. But I dont fully understand why shades are used over colors for setting the balance? Is it because the sensors work in the 3 color system and the shades are "neutral" to all of them? I dont think i am wording it right...

How could we detect a color cast in a red color? Is it too much red or not enough? There is no way the tool can know what color that red object ought to be, and then subtract out a little excess.

Whereas, pure gray shades are neutral (colorless). Gray (and white and black are just special shades of gray) is a neutral color ... if pure, then neutral has equal RGB components ... no color cast ... which computers can measure and detect that. If what we know is a pure gray was instead seen as RGB( 100, 100, 120), then it has a blue cast, which can be removed. We know exact degree, but we do have to know it was neutral though (it should have been neutral).

When we click the White Balance mouse tool on a neutral white or gray shade, we are saying "Computer, we KNOW this shade is neutral, it ought not to contain any visible color cast, so remove any color cast you detect there, and apply that correction to the entire image". And it does, so that spot does become equal RGB component numbers then, and our image becomes perfect white balance (no color cast).

Pure gray shades, and white, are specifically "colorless" by definition, and so any false color is easily detected. White is even better, because it is lighter, and color cast is easier seen than in something rather dark, where it doesn't show up as well.

It is after all named White Balance, the idea is to balance whites. Gray works too (sure, there are off-color grays and whites, but pure gray or white is neutral color - equal RGB components). Many white things found in the picture (church steeples, white shirt collars, paper envelopes, etc) work pretty well, but better, to actually know, we can we provide our own KNOWN gray or white. But many shades of gray are too dark, less effective, hides color cast. White is more bang for the buck.

In earlier digital days, the correction method was to align the right ends of data in the three RGB channels in the histogram, which assumes there was some bright white in the scene. This is still what the Photoshop Auto Levels does, aligns the right end of the three RGB channels (with a small specifiable clipping). This can magically restore the color of faded pictures (somewhat), but it can also be quite wrong too, if no bright whites. There will be bright whites after that correction is done.