[argyllcms] Re: Creating a camera profile with ColorChecker Passport Please Help
- From: Ben Goren <ben@xxxxxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Fri, 12 Jun 2015 14:30:05 -0700
On Jun 12, 2015, at 11:37 AM, Brett Howard <brett@xxxxxxxxxxxxxxxx> wrote:
I feel like I need to get over the first hurdle of just getting the dang file
to be able to be read.
If it's a problem with scanin recognizing the file, as I seem to remember was
the starting point...the quick-and-dirty answer is to use Iliah's RawDigger
instead to extract the chart values.
If that's not an option, the first most common problem is underexposure. You
might have heard of a technique called, "ETTR," or Expose To The Right, meaning
the right (bright) side of the histogram. There's a lot of sordid history
behind that technique...it never really should have existed in the first place,
and only does because camera manufacturers design their in-camera meters to
underexpose -- and then apply exposure compensation with a film-like tone curve
in their development engines. This was done to protect highlights, since
overexposure is relatively unforgiving in digital cameras...but the
implementation is quite problematic in all sorts of ways. ETTR is intended to
compensate for that underexposure, but most ETTR techniques have problems of
their own.
What you're looking to do is to _correctly_ expose your image, such that an
object that reflects 50% of the light that hits it produces a value in the RAW
file that's 50% of the maximum value for that particular file format. Another
complication...this is in linear gamma space, as that page I pointed you to
describes.
Once you've got exposure correct, the next big problem for scanin is going to
be cropping and geometric distortion. Although scanin can deal with some of
that, it has its limits. The closer your target is to being perfectly square
and centered and almost but not quite filling the whole frame, the happier
scanin is going to be.
Assuming you're typing everything correctly, scanin is quite reliable at
recognizing properly exposed and framed charts, so start on that end of it.
Cheers,
b&
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