Grey Caps and cave photo color correction

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Grey Caps and cave photo color correction

Postby pj » Dec 14, 2006 10:19 pm

About a year and half ago, I took a week long photo class at the Maine Photographic Workshop in Rockport. The course was called The Digital Landscape, which I thought was in the metaphysical sense of a vast landscape of opportunities, etc. :shock: WRONG! It was really about landscape photography in particular and thus not about printing which is what I really wanted help with. In any case, the instructor was Stephen Johnson (sorry, not Steven Johnson of forum notoriety...), a world renowned pioneer in digital photography. A great class, just not quite what I wanted.

In any case, he just introduced a new simple device to help with color correction. It is called a Graycap and is a simple, light grey colored 1" square that has an adhesive back. You usually attach it to the inside of your lens cap. It differs from an 18% grey card used years ago for metering your exposures. It is a lighter color, closer to a normal exposure value.

In any case, the idea is that you take one photograph with the Graycap included in the image, using the light source you use for your photograph. You can take the rest of your images without the Graycap included. When you sit down on your computer to process the images, the first thing you do is open the image with the Graycap. Go to the Levels Adjustment Layer, highlight the middle eyedropper (the Set Gray Point eyedropper), then click on the Graycap portion of the image. It immediately sets that as a neutral value, giving you virtually perfect color balance in your image, no matter what your lightsource was. Since the Graycap has been manufactured to exact standards with the R, G & B values being exactly equal to begin with, you know that clicking on it makes the image color shift to the correct balance. You then only need to adjust its brightness if is seems too bright or dark as a result.

Once you've done that with the Graycap image, you can drag that Levels adjustment layer directly into any other images you've taken using that same light source and it will balance them as well. All this takes the guesswork out of the usual advice to "choose a location that you think should be a neutral color balance". That advice is usually subjective at best and frequently wrong at worst. Using the Graycap means that what you think should be neutral really IS neutral by design, not guesswork.

As a purveyor of cave photography equipment, I may carry them later on as a great way to improve your color balance in cave photos. In the meantime, they are available from Stephen Johnson at his website: http://www.sjphoto.com/graycap.html . They are cheap, 3 for $15 and worth every penny. :exactly:

Peter Jones
Shot in the Dark Cave Photography
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Postby John Lovaas » Jan 16, 2007 10:11 am

Howdy Peter-

Thanks for the tip- I just ordered three for myself!

I've played with the QPsoft color cards and software, and although they are useful, these "mini-swatches" seem much more cave-friendly and idiot-proof(the idiot in question being me). Plus, I will stick a Graycap on my GSA photo scale(from geology-outfitters.com) and will be able to show not only how big(or small) something is, but also just what color it is!
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Graycaps...

Postby pj » Jan 16, 2007 11:14 am

John: Glad to hear it. Let me know how you like it.

Peter
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