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From: Paul N on 18 Jun 2005 18:33
Just getting up to speed with color managed workflows, I read some
interesting stuff such as the articles by Norman Koren and thought I
understood... but I don't: what I see on the screen is totally unexpected.

The setup is the following:
- Photoshop CS working color space set to sRGB
- Images are sRGB (confirmed in statusbar of PS)
- Monitor calibrated using Spyder; ColorVision LUT loader runs at system
startup

My assumptions are the following:
- Since picture color space and PS working space are identical, image RGB
values need no recalculation when image is opened in PS
- Monitor profile works system-wide (video card LUT) so PS does not have to
care about it.
- When I open an image in a *non color managed* app such as Irfanview,
essentially the same takes place: RGB values are sent to the video card
unchanged and the color correction is done via the LUT
- Conclusion: colors should look identical on screen in PS and Irfanview

To my big surprise, the images in PS and Irfan look *different*: the colors
in PS are more saturated and dark grays are darker.

The article by Norman Koren says that PS is using the *default monitor
profile*. For what purpose does PS use the monitor profile?????
Clearly there must be something wrong with my reasoning. The move to a color
managed workflow only makes sense if you understand what's going on so I'm
eager to know.

Any help to clarify this issue would be greatly appreciated.
Paul




From: Bill Hilton on 18 Jun 2005 20:07
>Paul N writes ...
>
>My assumptions are the following:
- Since picture color space and PS working space are identical, image
>RGB values need no recalculation when image is opened in PS

No, there's an on-the-fly modification for display purposes only using
the monitor ICC file so you see the on-screen image colors as
accurately as possible, based on what was measured by your Spyder
during characterization.

>When I open an image in a *non color managed* app such as Irfanview,
>essentially the same takes place: RGB values are sent to the video card
>unchanged and the color correction is done via the LUT
> Conclusion: colors should look identical on screen in PS and Irfanview

No, the non-color managed apps don't use the monitor ICC file so the
colors are different, as expected.

When you ran the Sypder software you first set black and white points
and white balance, which is the "calibration" step, and all programs
take advantage of this. Then the cal software displays colors of known
values on the screen and the puck measures them and eventually the ICC
profile is generated which changes the displayed colors to match the
known values, as closely as possible (the monitor ICC file is actually
a very tiny matrix). This is the "characterization" step. Color
managed programs use this ICC profile, non-color managed programs
don't.

You can see what your file *should* look like in a non-color managed
program by temporarily ignoring the monitor profile, which is done with
View > Proof Setup > Monitor RGB. Typically if there is a very large
difference between views it often means the profile is not very
accurate, I've found. You should see saturated colors changing if you
toggle this on/off (cntrl-y) but nothing earth-shaking for most colors,
at least on my monitors.

Bill

From: Paul N on 19 Jun 2005 07:49
Thanks Bill, the 'Monitor RGB proof' setting indeed results in the same
colors as I see in IrfanView.

Your answer raises new questions, see below.

Paul

"Bill Hilton" <bhilton665(a)aol.com> wrote in message
news:1119139635.248388.70070(a)o13g2000cwo.googlegroups.com...
> >Paul N writes ...
> [...]
> When you ran the Sypder software you first set black and white points
> and white balance, which is the "calibration" step, and all programs
> take advantage of this. Then the cal software displays colors of known
> values on the screen and the puck measures them and eventually the ICC
> profile is generated which changes the displayed colors to match the
> known values, as closely as possible (the monitor ICC file is actually
> a very tiny matrix). This is the "characterization" step. Color
> managed programs use this ICC profile, non-color managed programs
> don't.

The way you explain it, the cal step would not be recorded in the ICC file
and would be a manual step (tweaking the monitor's controls). Yet, the LUT
downloader *does* use the ICC file.

On my Dell 510m laptop, the LUT step makes a huge difference, accounts for
about 95% of the correction; The main effect is removal of strong blue cast
probably due to a very high color temp (9000K?). The Intel control panel
provides no manual control over this. Maybe the Colorvision startup app does
change the white point? Is this a software controllable parameter in video
cards?

Is it correct to regard the calibration as a 'coarse tuning' and the
characterization as 'fine tuning', in other words is this 2-step process a
technical issue (video LUT not able to implement the fine tuning) or is it
more fundamental than this?

Tags contained in the ICM file generated by Spider:
- desc, cprt
- wtpt
- xyz values of rgb colorants
- gamma curves for rgb, all 2.199
- vcgt private tag
- tcpt private tag

Any web pointer or other reference greatly appreciated!
______________________________________________________



From: yesnno on 19 Jun 2005 08:38


Bill Hilton wrote:
>
> >Paul N writes ...
> >
> >My assumptions are the following:
> - Since picture color space and PS working space are identical, image
> >RGB values need no recalculation when image is opened in PS
>
> No, there's an on-the-fly modification for display purposes only using
> the monitor ICC file so you see the on-screen image colors as
> accurately as possible, based on what was measured by your Spyder
> during characterization.
>
> >When I open an image in a *non color managed* app such as Irfanview,
> >essentially the same takes place: RGB values are sent to the video card
> >unchanged and the color correction is done via the LUT
> > Conclusion: colors should look identical on screen in PS and Irfanview
>
> No, the non-color managed apps don't use the monitor ICC file so the
> colors are different, as expected.
>
> When you ran the Sypder software you first set black and white points
> and white balance, which is the "calibration" step, and all programs
> take advantage of this. Then the cal software displays colors of known
> values on the screen and the puck measures them and eventually the ICC
> profile is generated which changes the displayed colors to match the
> known values, as closely as possible (the monitor ICC file is actually
> a very tiny matrix). This is the "characterization" step. Color
> managed programs use this ICC profile, non-color managed programs
> don't.
>
> You can see what your file *should* look like in a non-color managed
> program by temporarily ignoring the monitor profile, which is done with
> View > Proof Setup > Monitor RGB. Typically if there is a very large
> difference between views it often means the profile is not very
> accurate, I've found. You should see saturated colors changing if you
> toggle this on/off (cntrl-y) but nothing earth-shaking for most colors,
> at least on my monitors.

The OS and the video card must play some role in using a monitor's ICC
profiles. What are they? I know how to select a monitor profile as
default in WinXP, but that's about it. What else is involved in OS?

Is choosing a video card important for color management and using ICC
profiles? For example, using the same profile, will the displays look
the same on the same monitor for different (but comparable quality)
video cards?
From: Johan W. Elzenga on 19 Jun 2005 08:51
Paul N <paul2n.replace-2-by-1(a)hotmail.com> wrote:

> > When you ran the Sypder software you first set black and white points
> > and white balance, which is the "calibration" step, and all programs
> > take advantage of this. Then the cal software displays colors of known
> > values on the screen and the puck measures them and eventually the ICC
> > profile is generated which changes the displayed colors to match the
> > known values, as closely as possible (the monitor ICC file is actually
> > a very tiny matrix). This is the "characterization" step. Color
> > managed programs use this ICC profile, non-color managed programs
> > don't.
>
> The way you explain it, the cal step would not be recorded in the ICC file
> and would be a manual step (tweaking the monitor's controls). Yet, the LUT
> downloader *does* use the ICC file.

No, it uses a Color LookUp Table (CLUT). That is not the same as an icc
profile. You could set the monitor to another ICC profile manually, but
that does not change anything you see happening on startup.

> On my Dell 510m laptop, the LUT step makes a huge difference, accounts for
> about 95% of the correction; The main effect is removal of strong blue cast
> probably due to a very high color temp (9000K?). The Intel control panel
> provides no manual control over this. Maybe the Colorvision startup app does
> change the white point? Is this a software controllable parameter in video
> cards?
>
> Is it correct to regard the calibration as a 'coarse tuning' and the
> characterization as 'fine tuning', in other words is this 2-step process a
> technical issue (video LUT not able to implement the fine tuning) or is it
> more fundamental than this?

No, that is not correct. It's two entirely different things. Calibration
is setting the monitor to the best possible settings. Using a profile is
trying to compensate for physical differences that exist between
different devices (different monitors, monitor and printer), to make the
colors look as similar as possible on those devices (of course within
the limits of those devices).

Let me illustrate it with a practical example. Suppose your monitor
isn't too good at displaying very saturated yellow colors, but your
printer can print them very well because it uses pure yellow ink.
Without using profiles, your prints will have much more yellow
saturation than you thought they would have when you previewed them on
screen. Using your monitor profile, your computer can compensate for
this by increasing the yellow saturation when the image is sent to the
monitor, so it looks more like the print (within the limits of the
monitor. Colors that cannot be displayed, still cannot be displayed).
Likewise, it can desaturate the yellows a bit when sending the image to
the printer. As a result, the print and the preview on screen will match
much better. That is what profiles are for.


--
Johan W. Elzenga johan<<at>>johanfoto.nl
Editor / Photographer http://www.johanfoto.nl/
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