If it's White Balance, how come you can use a gray card?

Question

On some digital cameras you can set the White Balance manually. If it's White Balance, how come you can use a 18% Gray card to do it?

Charlie, in a digital world, white cards & gray cards have a lot to do with white balance.

I seem to remember something about exposure, metering and the Zone System from when I was 18, some 38 odd years ago, and sold everything I had and borrowed everything I could to take the 3 day intensive workshop in Yosemite that Ansel Adams personally gave once a year.

Answer 1

use the gray card for white balance. the gray card is color neutral, but it offers the normal reflectance of a typical subject. because of this, it allows you to set camera white balance using the same exposure settings and lighting as you will be using to get the shot. Using a white card can reflect so much light that it may drive the ccds into clipping so the level set this way can be totally bogus. Also remember that this method does not work for flash photography or mixed flash and tungsten light.

The term "white balance" has to do with setting the relative gain settings of the red, green and blue image channels and is an electronic adjustment. Our brain compensates for what we see, and an object we know to have neutral reflectance (a white shirt for instance) we interpret was white irrespective of the color of the illumination source. Film and digital cameras are not quite that sophisticated, but we can help out by telling the camera that a certain subject is neutral (ie the gray card) and it will adjust to that.

Answer 2

The 18% gray card doesn't have anything to do with white balance. White balance has to do with the color of the light source while the card involves the amount of light falling on the subject. So, the card is used to determine the correct exposure using a reflected light meter. Putting the card in the subject's position and metering it will give you an average meter setting that will result in an exposure that (generally) gives the greatest range of grays from white through black (from shadows to highlights). For example, you're looking at a great scene with a lot of bright sky and dark foreground. If you use the camera's meter setting the sky will be gray and the detail will be lost in the foreground because it will be very underexposed.

TTL spot metering and in film cameras and the whole range of metering possibilities in digital cameras has all but done away with the 18% card. But if you're still (or have returned to) shooting film then learning how to use the card makes it a valuable tool. The next step up from using the card is learning the Zone System of exposure control which is how Ansel Adams made his rich images. His negatives were perfectly exposed.

This may be TMI but your eye can discern a brightness range of about 1:10,000. In other words the dimmest object your eye can see is about 1/10,000 of the brightness of the brightest you eye can resolve. A quality b&w film can only resolve a range of about 1:1000 and the best glossy photo paper can only reproduce a range of 1:100. On a bright day the highlights in a scene can be 100,000 times brighter than deep shadow areas. That's where the 18% gray card comes in. It will give you an exposure reading that will capture as much of the middle range as possible. But the limitations of film will cause loss of detail in the darkest and brightest areas. Understand? Or did I just confuse the issue even more for you?

Answer 3

It very well could be your camera model. Some have pre-set colors that will throw your adjustments off. Start with your user manual, and see what the specific instructions are for bright sunlight photos. Now, that said, Bright sunlight is a truly crappy way to photograph a painting. If you want to photograph a painting, take it indoors, into a well illuminated room with a white background (sheets work pretty good. THEN set your white balance, I'm sure you will have much more vibrant colors...

Answer 4

White balance in the terms from a digital standpoint is measuring the COLOR of the light source or Kelven (light tempeture) that a photograph will be taken in. A white card or the backside of a gray card can be used to set the white ballance in the camera. The 18% Gray card is used to get a light reading or a correct shutter speed for proper exposure for any given F/stop

Answer 5

Kelvin difference between mid grey and white in kelivin isnt as extreme as(reading white instead of grey) in exposure, however it is there,

you can white balance off anything (people do it by pressing auto and pointing at a scene), white is best - you can use grey.

White balance is balancing for white balance, on professional TV cameras they have black balance as well.

Try some exposures using white balance with a white card then do the same with a grey card, there is a difference.


White for white balance, grey card for exposure - black for black balance.

So anyone can take a white balance off grey if they want to mess around in photoshop later,

white balance on auto is what most people say here? me i make images in the camera, if shooting daylight film under tungsten then i may or may not use a blue filter (on the lens not PC) to correct the colour cast

on digital still or video camera (pro or ameteur) i white balance manaully on white paper to corect the cast/white balance, then i do a hand reading or grey card reading for exposure, photoshop is down town to me, I try to make it in the camera.

start using whitie to do your white balance then you will always get perfect results, grey for white balance will throw your shots out a few hundred or two kelvin depends on cast and intensity etc, may see it sometimes sometimes you wont

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Answer 6

I dunno about that. I use a bright white sheet of matte finish photo paper for a custom white balance. I guess 18% Gray is just "dark white" as it is neutral. It will notbe reflecting any colors into the sensor as you set a custom white balance.