Naive question: How is / how much better is an "official" gray card than a simple sheet of white paper for this purpose?

Western Infidels: I think gray is better because it is more in the middle of the color spectrum.

Also, if you do not have this card, the palm of your hand (regardless of ethnicity) is only a stop or two away from the neutral gray. How this would work in photo software I do not know.

One reason may be that a lot of white papers have optical brighteners added, which boost the amount of blue light reflected off them to make them appear 'whiter' and so throw off the color balance of the photo.

why dont you just use the card and a spot meter to take the accurate reading on exposure instead of cheating and doing it in photoshop....!

what would you do before photoshop was invented?

learn to take correct exposures and forget photoshop.....

when we went from film to digital it seems we lost 100 years of photography experience..........just take any old image and 'fix it in photoshop'.......god i've heard that 100 times in the last 10 years...hahaha.

when you go into the darkroom to make prints...how do you use the gray card there....oh wait....you dont....you print on a inkjet printer..not in a darkroom.....

I used to carry a Kodak Photoguide mostly because it had a pocket grey card. You can buy a big grey card for the same price and cut it into pocket-sized cards. Heck, give them away for Christmas.

Metering from the grey card is great for exposure, but setting white balance from it kinda fussy in some cameras.

The whibal folks seem to think that their material is the most accurate, and the hard plastic seems more durable than this strip. Unfortunately, they are also more expensive. Does anyone have any experience using those?

Dudes, it's not about exposure. It's about color balance. These are not at all the same

The OP has succeeded in re-discovering the wheel. I have a Kodak Gray Card that I think I bought when I was in graduate school, 1970, and earning some part time photography work on the side.

A gray card is used for two things. As the OP mentioned, for color balance. In that case it is included in the image area of the photo. Someone printing from film or photoshopping a digital image can then use it to correct color balance/color temperature.

A gray card is also used for exposure determination. Instead of measuring light reflecting off a random collection of objects, you use a spot meter to measure the card.

The Kodak Gray Card has a white side, too. It is IIRC 8" x 10" and is very stiff. If you're serious, you should own one. Newer than mine.

@ Western Infidels: Not a naive question at all. White paper could work in a pinch, though it wouldn't be as accurate as the neutral gray of this QPcard, or a similar product. Using white paper, you have to be careful not to overexpose, in which case you wouldn't have any information for your imaging software to interpret. Also, papers vary–some will be warmer, some cooler–so they can't be relied upon as an absolute value.

As Peter pointed out white balance and exposure are two separate issues. The Kodak Gray Card, which I also used when shooting film, is helpful in determining exposure but not white balance. It provides an 18% reflective gray, but it's not a neutral gray.

Since digital cameras have histograms with accurate exposure info, a traditional 18% gray card is no longer so useful.--es

In most situation, I don't bother with the grey card (which I always have with me) as the camera seems to do a good enough job. I mostly use it for staged photos. The grey card I got a few years back to replace my (rather old) Kodak is both neutral grey and 18% reflective on one side and white on the other. I have both full sheets (8x10) and pocket size (4x5) versions.

i would just like to correct a misconception here: some commenters have disparaged the use photoshop with these gray cards.

first off, photoshop is really just the digital equivalent of the film dark room. because it's software, it's easier to use compared to fumbling with chemicals and negatives in the dark, but it doesn't mean it isn't a legitimate tool to use in modern digital photography. to put it another way, no one protests that modern architecture is all done with autocad type software; you don't see engineers nostalgically longing for the days of the slide rule and the t-square.

nextly, gray cards are not exclusively used for digital photos; they are in fact, part of the tools of the trade even in the days of film. simply put, it's hard to develop a color picture and get accurate colors, regardless if by "develop" you mean using chemicals in a dark room or mouse clicks in software. determining the correct shade of color is hard because it is very subjective and is affected by changing environment unless there is a fixed value we can use as reference.

I use a WhiBal and it works well. You need a grey card, not white, as it provides a middle range of values in all 3 RGB channels. Since white is more frequently 'blown out' in one or more color channels, it is less reliable. In fact, Camera Raw or Lightroom will refuse to do a white balance using a location that is too white. In my experience, the Kodak grey card is not netral grey; but then mine is quite old. Simple experimentation will answer this question. An accurate grey can solve a lot of color balance problems, but does not necessarily create the image you want. Light sources with different color temperartures need to be balanced. If you photograph is during the 'golden hour', a grey card can totally wipe out that warm low angle sun effect. As with everything, a grey card provides information, not intelligence.

Bubba, Winston..

When I was young we didn't need cameras and such. We had a burnt stick and some tree bark and made our pictures that way!

btw, there is lots of manipulation done in darkrooms - pushing film, cropping, dodging, burning, colorizing, fixing scratches and dust spots. Same goals - a 2 dimensional image of a 3 dimensional world. Just using different tools.

Instead of a gray card like this, you can also use a microfiber lens cleaning cloth that is 18% gray. They double as gray cards, saving you the trouble of carrying both. Plus, the cloth is easier to carry because it can be tucked in your pocket or other odd places where a card would get damaged. I use an 8"x8" microfiber gray cleaning cloth I bought for $6 from Adorama, but they're available from other sources too.

(Now, to be honest, I have to admit I haven't tested the cloth to make sure it's really comparable to a gray card, though. I'm just _assuming_ it is.)

I use a similar card that I was able to get for free at Lowes (or Home Depot...)