Re: Colorimetric Accuracy in the Field
Re: Colorimetric Accuracy in the Field
- Subject: Re: Colorimetric Accuracy in the Field
- From: Ben Goren <email@hidden>
- Date: Mon, 03 Jun 2013 20:16:01 -0700
On Jun 3, 2013, at 7:03 PM, Robin Myers <email@hidden> wrote:
> On Jun 3, 2013, at 6:13 PM, Don Schaefer wrote:
>
>> Then what?
>
> Set up your camera and a color chart holder, an artist's easel works well, outdoors in the summer at noon.
While there's much good advice in Mr. Myers's words, there are many ways to follow the instructions exactly and still end up with a less-than-satisfactory profile.
Some variations I'd suggest...well, hesitatingly, I'd suggest using a light tent (outdoors at noon in the middle of summer) to illuminate the chart. It doesn't solve all the problems of properly illuminating a chart in an uncontrolled environment, but it solves more problems than it creates. For better results, you'll have to devise a contraption that blocks extraneous reflections and specular highlights -- not a straightforward task, especially if you still want some portion of skylight to contribute to the illumination of the chart.
I've already beaten to death the amount of pre-cooking of the data that most raw processing engines do that can't be turned off or reversed, which is why I recommend Raw Photo Processor or one of its other free / open-source cousins. If that's an option, you can precisely and perfectly normalize white balance and exposure using the method I detail here:
http://trumpetpower.com/photos/Exposure#The_right_way_to_do_it
If that's not an option, then here:
http://trumpetpower.com/photos/Exposure#How_to_make_the_most_of_a_bad_situation
you'll find my recommendation of how to get not-quite-so-bad results out of Adobe Camera Raw and similar raw developers.
And I can't stress enough the importance of the chart. The ColorChecker SG is barely adequate. You can make your own, far superior chart...and, in so doing, you'll learn both why the commercial charts mostly don't cut the mustard and why almost nobody could afford to buy or manufacture a really good chart.
Once you've got a good profile, when you're out in the field, instead of photographing a gray card and doing an eyedropper white balance, you'd photograph a chart (and the ColorChecker Passport is ideal for this purpose) and follow the same steps at the links above to normalize white balance and exposure. You'd apply your profile...and, within the quality of your workflow, that's all there is to it.
Cheers,
b&
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