[Digikam-devel] CMS beginner question

[Thorsten Schnebeck]

Am Donnerstag 09 Februar 2006 23:21 schrieb F.J.Cruz:
> A Color Management Module (we are using Little-CMS) is a conversion engine
> which translates the pixels colors from a color space to another color
> space. A color profile is a set of tables of parameters and mathematical
> matrix coefficients or raw color values describing the target gamut in a
> standard format.
[...]
> - Inputs profiles (cameras and scanners): an input profiles describes the
> color gamut of a camera or scanner. All cameras and scanner "read" the
> color in RGB. These are "one direction" profiles, this is,  we can
> translate from device coordinates to absolut coordinates. The profile can
> also contain one dimension curves that can be linears or non linears,
> altough the purpose of theses curves are not specified and depend on the
> app which buids the profile.

Ok, I make a new example. Lets focus on two colors, black and white :-)

My cam produces a jpeg, 8-Bit per channel so white is 
RGB8=(255,255,255) and black is RGB8=(0,0,0)
If I use the RAW mode white is
RGB12=(4095,4095,4095) and black is RGB12=(0,0,0)
When I view a 16Bit PNG the color white is
RGB16=(65535,65535,65535) and black stays RGB16=(0,0,0)

So now I want to start using CMS. The cam's  JPEG are calibrated in sRGB. When 
using RAW I have to apply an external profile. Like you said in your 
description a input color like RGB12(white) will be translated to a target 
like e.g. RGB16(white) . Thats my problem in understanding this stuff. The 
color white is well defined in all color spaces, so when I use CMS why do I 
have to manually adjust the target color range. White should be white, or?

Maybe the problem is, that we did not talk about format conversion so far but 
only about device color ranges. Is a PNG-16bit file handled like an output 
device?

> > Ah! So, what about showing at least the filename when the "vendor
> > tag" is empty?
>
> I guess you are talking about info messages in dialog setup. These messages
> show the path to the profile.

I attach a screenshot of the setup dialog. Please look at the monitor profile 
(Monitorprofil) its set-up, as you see in the the info box but not shown in 
the dialog.

Thanks for your patience :-)

Thorsten
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