[argyllcms] Re: AW: Re: Comparing sRGB and AdobeRGB
- From: ternaryd <ternaryd@xxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Wed, 17 Feb 2021 06:12:04 +0100
On Tue, 16 Feb 2021 14:27:19 -0800
"Wire ~" <wire@xxxxxxxxxxxxxxxxx> wrote:
Cris, To clarify, Herman-Joseph is saying
something further than basic CM. He is
saying that in a fully color-managed display,
an sRGB image which is limited as such by
definition, renders more vividly on his
display in Adobe RGB mode with corresponding
profile, than the same display in sRGB mode,
with same profile, and moreover he's at least
considered that the sRGB mode has good
coverage.
Actually this behavior is really easy to
understand and quite obvious, but I'm having a
hard time putting it into (few) words.
The point I was trying to make is to focus on
the fact that the values in an image file--as
well as those sent to a monitor--are relative,
the highest value being 100% of something. And
most of the time, this something is not the
same for the monitor as for the values in an
image file. In absolute terms, this 100% is
meaningless until defined by additional
information.
Here is what happens, if you try to display
sRGB values as if they were values in Adobe
RGB:
Visualize the xy-diagram with the triangles for
Adobe RGB and sRGB gamuts. If you draw a line
from white to the border of the diagram (locus),
there'll be two intersections, one with each
gamut's triangle, and (most of the time) with
the sRGB's triangle first. So the distance from
white (completely unsaturated) to the end of
the gamut (maximum saturation in that color
space) is simply longer (reaching a higher
degree of saturation) with Adobe RGB than with
sRGB. So the 100% of sRGB will be displayed as
the absolute saturation of 100% in Adobe RGB,
and that yields a different color which, for
sRGB, is out-of-gamut.
This needs to look more vivid. No surprise at
all.
And this is exactly what Herman-Joseph
described, and it's the only explanation.
Therefore, it needs to be a fact that the values
in the image file, in sRGB are never transformed
to the values in Adobe RGB.
The rest of the story was already pointed out
by others: The CM has no idea where the pixels
to be displayed came from, or in which color
space they had been encoded. It doesn't convert
anything. It just provides the applications
with the information where it has to convert
the values to, and it does so only if asked.
In the described scenario, for what reason
ever, neither the application did perform such
a conversion.
Herman-Joseph has two choice to make it happen:
He can embed a profile into the image, or he
himself can tell the application, that the
image file is encoded in sRGB. In both cases,
the application should perform the
transformation, and the image should look
correctly.
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