[argyllcms] Re: Camera profiling with bracketing

  • From: Rishi Sanyal <rishi.j.sanyal@xxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Thu, 24 Feb 2011 18:01:12 -0800

Don't know if this'll help or is relevant, but when I experienced
flare in IT8 target scans due to scanner optics, the flare was
generally dependent on how light the patch to any side of a patch in
question was (the light the patch, the more light that bled onto an
adjacent patch).

This affected quality of profiles.

So what I did, manually, was to take such problematic patches, select
them using the marquee tool, then copy & paste over the original patch
rotated 90º using the 'darken' blend mode in Photoshop. I did this
also for 180º & 270º for each patch. This got rid of flare on most
patches & resulted in a profile that showed less clipping of dark
colors (since flare artificially brightened a lot of dark patches,
which the profile tried to compensate for by darkening those colors).

Of course, this only works if parts of the patch in question do not
suffer from flare.

Also don't know how accurate this technique is but, hey, thought I'd
throw it out there. I'm sure someone could write a script to automate
this using patch detection (even from an IT8 outline that you overlay
over the target shot).

-Rishi

On Thu, Feb 24, 2011 at 5:33 PM, Graeme Gill <graeme@xxxxxxxxxxxxx> wrote:
> Iliah Borg wrote:
>>
>> Such shots are done using tripod and remote, so if user (or scanin)
>> samples one chart
>> all other locations are the same. I prefer manual sampling (like it is
>> done in RPP)
>> because that allows to avoid any imperfections right from the start. It
>> seems that
>> profiles with manual sampling go easy to 6dE max, while with scanin they
>> are usually
>> about 12 to 20 dE.
>
> I'd be interested to have a sample that shows such a difference, as scanin
> should work better than that.
>
>> I would start with a merge utility that re-calculates spectral reference
>> for each
>> individual .ti3 file based on the exposure of grey patches (around neutral
>> grey)
>
> Right, this sounds much like HDR image merging. It is also a bit outside the
> scope of the next release :-)
>
>> filters veiling glare can reach 2/3 EV easily when shooting a chart.
>> Adding a simple
>> black trap (hole) to a chart allows for a good estimation of veiling
>> glare.
>
> That would only work for a specialised chart though. I wonder if there is
> a more general way of estimating flare.
>
> Is it reasonable to assume that flare decreases in line with everything
> else if the exposure is reduced ?
>
> Graeme Gill.
>
>

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