Linary Loc: UK

The densitometer I use is a printers reflective densitometer. Designed to measure spots of colour on colour bars and spot colours on a printed sheet. You can get an understanding of the device here: http://www.xrite.com/categories/portable-spectrophotometers/exact

This is not the one I use, but fairly similar.

jerryc41 Loc: Catskill Mts of NY

Lots of gray info.

http://www.bythom.com/graycards.htm
http://digital-photography-school.com/how-to-use-a-gray-card-to-get-more-accurate-exposures-and-color/
http://www.digitalphotomentor.com/how-to-use-a-gray-card-for-custom-white-balance-and-metering/?utm_source=Digital+Photo+Mentor&utm_campaign=f5fb80c5b2-DPM_Blog_Broadcast&utm_medium=email&utm_term=0_ec33f1d0c3-f5fb80c5b2-263056661&mc_cid=f5fb80c5b2&mc_eid=fddc3ab094

lloydl2 Loc: Gilbert, AZ

in photgraphy and within acr and lightroom gray is defined as any shade between white and black that has equal values of Red Green and Blue. The WB eye dropper clicked on any color will change that color value so that RedGreen and blue all have the same value somewhere between 0 and 255.. Middle gray is when that value is 128 for each r g b. Appearance of cold (blue) could mean that your monitor is not properly calibrated. Before you click on the gray card hover over it with the wb eyedropper and note the values of RGB they should all be the same number andif it is a 50% gray card they should be 128 or very close. If it is off than it could be your monitor or the card itself. There is also confusion about 18% gray vs 50% gray. Your camera meter is set up to return a meter reading where 18% of the scene is a tonal level of 50% gray (this is a light value and not the color gray) It equates to zone 5 on ansel adams zone system...

PGHphoto Loc: Pittsburgh, PA

If you are trying for accurate white balance (and NOT exposure) you need a white card. The temperature is set based on trying to get white to look white under the current lighting conditions.

A Gray card is for getting exposure correct based on reflected light. An 18% gray card approximates the reflectance of skin tones. The 2 are quite different and you will not get accurate colors in camera if using a gray card for white balance.

clickety

That is my experience as well.

jamesl Loc: Pennsylvania

I have owned many grey cards from different sources and if they are set side by side they do not necessarily match exactly in color. The shade of grey varies some but all that really matters is that the RGB values are all the same making them neutral. Any neutral shade of grey will work perfectly well to set white balance to eliminate color casts.

A good true 18% grey card is also useful to check exposure when shooting since it is what the camera lightmeter is trying to adjust thescene/subject to be.

PGHphoto Loc: Pittsburgh, PA

The only way to be certain that a gray card has the property of R, G and B values being the same is to make it a white sheet. All printers - commercial and home - use different techniques to attain black. Most are not true black but a variant of blue and brown. This is why when a printed black fades it sometimes appears to be blue and does not just fade to gray. This is not as important when shooting stills since you can easily modify in post so you could get away with using a gray card for white balancing. I am willing to bet that the average person without a 199, 199, 199 (#C7C7C7) reference card can't see a 199, 201, 204 (#C7C9CC) as not true gray. For video - especially broadcast video - you will never see anyone using anything but white to do a white balance and also will make sure all cameras use the same source for their white balance.

The consideration is that a non-white reference can absorb some wavelengths that will cause a camera to mis-identify the appropriate white setting. The naked eye normally can't see a mild yellow shift in ambient lighting when reflected on a gray card but a camera can. Why go through the hassle of getting a white balance that you can't rely on because you used a gray card ?

Wall-E Loc: Phoenix, AZ

Never seen a '50%' grey card.
All the ones I know of are 17-18%.

Dennis833 Loc: Australia

The answer to your question is yes, grey cards are different. When I shot art works I include my 30 year old Kodak grey card. I have two newer cards that give incorrect results. I shot on AWB and prefer to eye ball the raw files. I open the tiffs in photoshop and use the eye dropper tool. This gives me a very accurate match.

Bill Emmett Loc: Bow, New Hampshire

I use a Color Checker Passport, by X-rite. Just shoot a test shot and view it in LR and work with the light on the subject. There are several Utube videos on the process.

B

Lenshood Loc: Maine

Count me among the confused. I'm an old analog shooter. Knowing what kind of light you are shooting in seems much more important than post production color correction using a gray card. Eighteen percent gray cards are more valuable when exposing pictures because all light meters are calibrated to an eighteen percent gray card. Theoretically, if you place a gray card in the scene, meter from it, take the picture exactly as you should, develop the negative perfectly, and print using minimum time/maximum. Black standard, you should get a print in which the card is precisely eighteen percent. Color balance is easy, 5500 Kelvin for daylight, 3600 Kelvin for tungsten, 7300 for flourescent. Vary to taste. To me, the gray card is more pertinent to exposure than color balance.

Lenshood Loc: Maine

I agree with you, but would indicate that 18% gray is one stop darker that skin tone.