Re: Primer on photographic exposure, etc.
Re: Primer on photographic exposure, etc.
- Subject: Re: Primer on photographic exposure, etc.
- From: Ben Goren <email@hidden>
- Date: Tue, 21 May 2013 07:15:00 -0700
On May 21, 2013, at 5:33 AM, José Ángel Bueno García <email@hidden> wrote:
> Hello:
>
> "If you are a fine art photographer, your target should
> reflect (pardon the pun) the media you are photographing."
>
> Do you mean IT8.7/1 for slides, IT8.7/2 for photographic copies and
> ColorChecker(s) for the rest of art objects?
The IT8 targets are good for scanning photographs. More patches would be nice -- always! -- but they have enough for good results and the distribution is good. That's especially considering that there aren't very many pigments to worry about.
I'm a huge fan of the ColorChecker Passport for field use to colorimetrically normalizing exposure and white balance. It's the only small chart I'd really consider for matrix profiles, but 50 patches really aren't enough for quality work. Even the ColorChecker SG doesn't have enough patches.
What you need to do is build your own target. You'll want as many different paint samples as you can practically apply, and ideally a few different tints of each paint. You'll also want to fill out the rest of the chart with as many patches as you need to get into the hundreds (ideally several hundred or more) patch range by printing on high-quality fine art (OBA-free) paper on an inkjet with as many different inks as possible. You can use your favorite printer profiling package to generate the patch colors. Print the chart, paint the paints, measure with your spectrophotometer, and you've got a better chart than any you can buy.
> What about the distance to the target?. If I have to reproduce original art
> on paper near DIN A3 size I don´t change the distance to reproduce a
> ColorChecker, and think is OK if the surface to reproduce is evenly
> illuminated by a single light source and that that is the way to
> characterize the sistem in a fixed condition.
As I noted in the previous email, what matters most is angle of view, not target distance.
But a single light source isn't going to give you even illumination unless it's very far away (such as the Sun). Ideal is a very large, very narrow ring light at 45° to the art. Two or more bare-bulb lights positioned in spots on an imagined virtual ring light work just fine, with more bulbs being better. I get great results with four Einstein flashes in a square. The traditional copy stand uses two lights to good effect.
Cheers,
b&
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