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Archive 2012 · 18% gray card; what magic?
  
 
splathrop
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p.1 #1 · 18% gray card; what magic?


Not sure I understand the science of this. Why is it better to use this for custom white balancing than a white sheet of laser printer paper, for instance? What difference do you see in the resulting colors? Any reason not to make one using Photoshop and your photo printerójust set the K value on CMYK to 18% and the rest to zero? Or would there be a better way to do it?


Dec 08, 2012 at 03:58 AM
gdanmitchell
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p.1 #2 · 18% gray card; what magic?


You could use various things including white pieces of paper. The gray cards have a few advantages though:

1. They are small and sturdy, often being made of material such as plastic which will stand up to more abuse that pieces of paper.

2. Paper is usually not really white - it tends to be slightly warmer or cooler toned than that.

3. The gray tone also gives you and accurate midpoint exposure, above which you would have whites and below which you would have blacks.

4. Many gray cards also include white and black patches - and sometimes more.

In reality, if you shoot raw, quite a few of us are happy in almost all cases just to set color balance by eye, subjectively and to conform to our preference rather than to an objective standard. (In certain types of publishing, particularly when product color accuracy is important, this might not be so appropriate.) In a lot of photography, objective accuracy is less important than making it look right - which may well mean warming or cooling the coloration of the image.

I carry a small gray card that includes white and black patches, but it turns out that I rarely find it to be that useful in the field. YMMV.

Dan



Dec 08, 2012 at 04:11 AM
sirimiri
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p.1 #3 · 18% gray card; what magic?


Grey cards are, in theory, an item made via a controlled process, with a specific intent. Nor do they cost that much.

Sheets o' "white" paper....?

You get the idea.



Dec 08, 2012 at 04:21 AM
Shutterbug2006
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p.1 #4 · 18% gray card; what magic?


A grey card is a neutral balancing tool.

Instead of basing color adjustments on white or black objects, a neutral balance determines the best adjustments using the average of all the light in an average scene.

An 18% grey card will let the camera and all of your post-production software know what color levels the overall exposure should produce. The use of the 18% gray card is basically to tell your camera, "look, the neutral grey is over here!"

White balancing using a white object can produce mixed results, because overexposed images all appear white.

You can color balance in camera (for each set of shots under similar lighting conditions), or take a shot with grey card, and use it later in post-production.

If you are shooting a portrait, have him/her hold the grey card in front of their face for a test shot and and/or zoom the grey card to fill the frame. Avoid reflections on the card.

When you process your photos in Photoshop, open the shot with the grey card. Enter the Image > Adjustments > Levels menu, and click on the middle eyedrop icon.

Save the level adjustment and you can load it for every other shot under the same lighting conditions.

Edited on Dec 08, 2012 at 04:27 AM · View previous versions



Dec 08, 2012 at 04:24 AM
BrianO
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p.1 #5 · 18% gray card; what magic?


splathrop wrote:
Not sure I understand the science of this. Why is it better to use this for custom white balancing than a white sheet of laser printer paper, for instance?


It depends on the card. Older ones (and some cheaper new ones) were meant to be an exposure standard, not a color standard, and they may not be spectrally neutral. Good ones, though, are good for both.

I know several photographers who do use white paper with good results, and one of them actually carries a binder with paper in different pastel tones for custom white balance. A slightly blue paper, for instance, will give a warm tone to photos (good for some portraits), while a slightly pink paper will give a cool look (good for snow scenes, day-for-night scenes, etc.).

It's all a matter of different courses for different horses; one can use the tools one likes just because one likes them.

Shutterbug2006 wrote:
...White balancing using a white object can produce mixed results, because overexposed images all appear white.


An important point, and why I wouldn't use white paper myself.


Edited on Dec 08, 2012 at 08:09 PM · View previous versions



Dec 08, 2012 at 04:25 AM
John Mills
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p.1 #6 · 18% gray card; what magic?


Camera meters see everything as 18% grey so it is perfect for getting correct exposures, but you must replace the card every now and then as they will not be perfect over time due to exposure.


Dec 08, 2012 at 06:44 AM
BrianO
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p.1 #7 · 18% gray card; what magic?


John Mills wrote:
...you must replace the card every now and then as they will not be perfect over time due to exposure.


Yeah, and even more so for colors. My Datacolor ColorChekr has a little red square in a window in the frame, and a matching square hidden from the light. When the first one becomes noticeably faded it's time to replace the card.


Edited on Dec 08, 2012 at 08:08 PM · View previous versions



Dec 08, 2012 at 06:59 AM
anthonygh
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p.1 #8 · 18% gray card; what magic?


Anyone using raw capture with a colour calibrated monitor doesn't have to worry about this...one can be an artist and use ones sense of aesthetics to determine colour balance.


Dec 08, 2012 at 03:37 PM
 

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DougVaughn
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p.1 #9 · 18% gray card; what magic?


I use my white balance card almost religiously because I'm color blind in specific colors and shades. No fun for a photographer. I use the card to get what should be "true" color, then warm or cool to taste. I still don't always trust myself and often ask my wife, "does this look realistic enough?"


Dec 08, 2012 at 03:46 PM
Photon
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p.1 #10 · 18% gray card; what magic?


The important points have been well covered above, but I'll add:
The 18% reflectance standard dates from film use and the gamma curve of "normally" developed film. Still, when a mid-tone gray object is placed in a scene with a range of tones and the digital exposure is adjusted to capture the whole scene, the gray reference will be exposed at a level that's good for adjusting white balance via custom WB or later raw development. You can shoot a white sheet in isolation and meter it normally - you'll get a gray sheet that's fine for WB, except that as already pointed out, "white" paper (and even cloth) often has a tint.
So, don't worry much about 18%, but look for a reference that's truly a neutral gray.



Dec 08, 2012 at 05:35 PM
Caleb Williams
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p.1 #11 · 18% gray card; what magic?


In addition for color correction purposes, an 18% gray card gives you some space between white and blacks and to find a hue neutral gray.

You can then average them in your editing software exactly (rather than using an eye dropper tool). Using that amounted of control can be important when you're printing photos.



Dec 11, 2012 at 11:50 PM
ross attix
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p.1 #12 · 18% gray card; what magic?


http://xritephoto.com/ph_product_overview.aspx?id=1257&catid=28&action=overview

X-Rite has this so covered.



Dec 12, 2012 at 12:11 AM
BrianO
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p.1 #13 · 18% gray card; what magic?


ross attix wrote:
X-Rite has this so covered.


As does Datacolor:

http://www.youtube.com/watch?v=QowwKLorHa8

I have one:








Dec 12, 2012 at 04:43 AM
Bieg
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p.1 #14 · 18% gray card; what magic?


BrianO
What bracket are you using to mount the passport?



Dec 12, 2012 at 04:57 PM
BrianO
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p.1 #15 · 18% gray card; what magic?


Bieg wrote:
BrianO ...What bracket are you using to mount the passport?


It's not a ColorChecker Passport, it's a Datacolor SpyderCHECKR, which is quite a bit larger than the Passport. It works similarly, and like x-rite's Passport it comes with software for camera calibration and post-production color balancing.

http://spyder.datacolor.com/portfolio-view/spydercheckr/

Not sure on the umbrella bracket; I have several, including Manfrotto, Lastolite, Photoflex, and RPS Studio, but I think that one is a cheap model from Impact:

http://www.bhphotovideo.com/c/product/298709-REG/Impact_3117_Umbrella_Bracket.html



Dec 12, 2012 at 09:08 PM





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