[argyllcms] Re: WP correction with ICC based CMS applications.
- From: János, Tóth F. <janos666@xxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Sun, 24 Oct 2010 00:03:51 +0200
UPDATE
Well, I managed to get 6500K white when I created a new document in
Photoshop CS5. So, I think my profile is OK. But there are some software
related "issues".
My previous test image was a white rectangle which I created in MS Paint
(Win7 x64 version) and saved in PNG format. As much as I know, MS paint is
not an ICC aware software. It measured ~5900K in paint.
When I opened this PNG image in Photoshop or IrfanView (CMS plugin ON), I
measured ~5940K. So, I assumed that "something happened".
When I used Photoshop to converted this image into the device profile and
saved it as a PNG format, spotread measured ~5640K on the IrfanView (CMS
plugin OFF) window. And it measured the same on the Photoshop windows, as PS
used the device profile for rendering. (If I enabled the IrfanView CMS
plugin on the converted PNG, I got a false result. A blue image. But this is
OK, because this ismage was already converted and tagged with a simple sRGB
profile, not the device profile...)
When I opened the unconverted PNG (which I created in PS) in IrfanView (CMS
ON), I measured ~5940K again.
Firefox 4.0b6 hehaves like IrfanView. (May be PS tagged the file with a V4
profile which is not supported by these softwares. Or.. I don't know...)
So, the profile works in Photoshop, when the image is correctly tagged. But
this is not enough for me because I want proper colors in Firefox AND
MPC-HC.
MPC-HC shows the same behaviour as IrfanView and Firefox. It does
"something" but not what I want. The image is processed because I can see a
yellowish but relatively smooth gray gradient instead of the uncorrected
bluish grays + yellowish 100% white.
So, I think that the MPC-HC implementation is broken. It uses littleCMS 2
which theoretically supports V4 profiles as well. But there are no profiles
here. It works from the device profile and user selectable presets (desired
gamma and rendering intent ; and an input standard preset which can be
auto,Rec709,Rec608, etc).
But it has to be enough because the source standard is defined. It knows
that Rec709 has D65 white and sRGB primaries. And the tonal response curve
is an open question in the "community" but the picked up one of the
possibilities (flat gamma 2.35, I think) but this won't affect the white
point adaption (which is D65 for sure...).
May be I should talk with the MPC team about this.
But I am not absolutely sure about this because it shows the same behavior
that "many" other softwares.
I also played with the MS Photo Viewer -> same as IrfanView or Firefox. But
it theoretically supports V4 profiles as well. I never measured 6500K here.
The only situation where I achieved the "correct" result is the new document
in Photoshop. (May be I forgot to check the PS saved image in MS Photo
Viewer.)
Any ideas?
PS.:
Does the -u switch in colorpro do anything with YXZ cLUT + matrix profiles?
(And can it play any part here? Or any other switches...?)
I am wondering what would happen if I get an ICC file for Rec709 and I
create a Perceptual B2A table with colorprof. May be MPC-HC would use it
when I set it to Perceptual intent mode. But it looks like it works without
the tables. (May be it creates it's own tables from the colorimetric data.)
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