Re: preview/photoshop - here's a possible solution!
Re: preview/photoshop - here's a possible solution!
- Subject: Re: preview/photoshop - here's a possible solution!
- From: Claudio Hoecker <email@hidden>
- Date: Fri, 14 Jan 2005 01:34:47 +0100
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Hi everybody,
I finally think that this is a Photoshop-Bug when PS is using Apple CMM
and IT IS NOT a Mac OS X issue!!! You wonder why? Well then, here's my
solution to get the (nearly) same (RGB) colors in Photoshop and Mac OS
X apps like Preview, Safari, Mail... (note, I did not test this on any
Windows system).
First, we need something as a reference, to make clear, that we all
talk about the same thing. For that reason, we will make use of Apples'
DigitalColor Meter and I recommend downloading the following set of
images for checking your display-calibration. The images are in an
archive "ECI Monitortest" and you can find them for free at
http://www.eci.org/eci/de/060_downloads.php
There is a .sit archive for Mac users (including TIFF) and a .zip
archive for Windows users (including BMP). The included manual is
German only, I'm sorry for that inconvenience.
Next, unstuff the archive and choose the image with the resolution that
comes closest to your display setting as your desktop background image.
Make sure that you DON'T SCALE the image, otherwise the Gamma-Area does
not work properly!!! I recommend setting your desktop preference pane
to CENTER the image.
Now, open up the exact same image in Photoshop (CS), DO NOT ASSIGN A
PROFILE and set your view to 100 %. In both images one pixel of the
image should match exactly one pixel on-screen.
Close/hide all other apps except Photoshop and the Finder. Close all
windows in the Finder. Clear your desktop from files and folders.
If you experience any difference between the gray background of both
images (for now, don't care about the gamma-area in the images), then
set your Photoshop Color Settings to the following setup (advanced
settings):
RGB Working Space: Display/Monitor-RGB (can be changed in Display
Preferences Pane) OR "ColorMatch RGB" OR "Apple RGB" OR Apples
'"Generic RGB Profile" (NOT "sRGB", NOT "Adobe (1998) RGB")
CMM: Adobe (ACE) (on my system, changing the rendering intent had no
impact, so you can set it to the preference of your choice. The same
goes for black point compensation).
NOTE: Both images should match in "color" now!
To verify this, open up the DigitalColor Meter (can be found in
/Applications/Utilities/ ). Select RGB 8 bit at first, to verify the
RGB values in the desktop background image and the image displayed with
Photoshop. You should read
R: 127
G: 127
B: 127
in either the Finder and Photoshop.
Next, select CIE L*a*b* in the DigitalColor Meter and read the values.
You should read the same values in the Finder and Photoshop. On my
system it was
L*: 60.478
a*: -0.004
b*: -0.004
Now tweak around with your Photoshop Color Settings, let's say, just
switch to Apple CMM or Apple ColorSync. The Photoshop view should
change slightly. Now read the Photoshop-image-RGB values again with the
DigitalColor Meter.
With my display-profile as RGB working space, it says
R: 128
G: 128
B: 126
L*: 60.755
a*: -0.117
b*: 0.867
With Apples' Generic RGB profile, ColorMatch RGB profile and Apple RGB
profile as RGB working space it says
R: 130
G: 127
B: 126
L*: 60.722
a*: 0.992
b*: 0.855
When I set sRGB IEC61966-2.1 as my RGB working space, it says with the
Adobe ACE CMM (Adobe (1998) RGB is in parantheses)
R: 107 (108)
G: 107 (108)
B: 107 (108)
L*: 53.033 (53,417)
a*: -0.004 (-0.004)
b*: -0.004 (-0.004)
because of the 2.2 gamma defined in the Adobe (1998) RGB profile and
the TRCs in the sRGB profile (it does not store a single gamma value,
but a curve with 1024 points). You'll notice, that the image is much
darker, but the neutral tones are preserved. You'll loose some
lightness values, due to quantization between 1,8 and 2,2 gamma, too.
Finally, switch back to Apple ColorSync / Apple CMM and read the values
for sRGB IEC61966-2.1 (Adobe (1998) RGB is in parantheses) as RGB
working space. In my case
R: 110 (111)
G: 107 (108)
B: 106 (107)
L*: 53.295 (53,678)
a*: 1.066 (1.062)
b*: 0.922 (0.918)
To confirm Photoshops' behavior with more colorful images and RGB
images with attached profiles you can try the same on your own. But as
the other images already was an RGB image, you can assume the same
behavior.
I also checked it with images with an attached profile and it worked
fine.
Conclusion?!
As you can see, all color values (RGB, L*a*b*) stay the same in the
FInder, Preview and Photoshop CS (with Adobe ACE and the correct
RGB-working space profile) but they only change in Photoshop when
changing the CMM from Adobe ACE to Apple CMM / Apple ColorSync or when
setting a "wrong" RGB-working space. Maybe Adobe is intentionally doing
something wrong to keep users sticking to Adobe ACE?! I should ask
someone at Adobe about that...
Finally, I hope this "not so short" solution helps you. As for me, I
now know how to set up my Photoshop color settings.
Regards,
Claudio
PS: The desktop background image is intended to check your display if
- - it has the correct gamma (if so, you should not be able to read the
value which your display is set to), if it does not - CHECK your
display and your display profile!,
- - it has some odd color distortion in the neutral area which covers
most of the screen,
- - the contrast/brightness is set up properly (if so, you should be able
to see the ECI logo in the big black and white boxes),
- - your profile or display creates "tone jumps" (don't know how to
describes this better)
- - your display / display profile creates color shifts in general.
I hope that there will be an english manual in the near future...
please check http://www.eci.org/eci/en/ if english downloads are
available.
PPS: For LCD/TFT displays I recommend modifying the image in a way,
that the main elements are in the center of the screen and that there
is a gamma-element in each corner to see how much impact the viewing
angle has on your display.
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