[argyllcms] Re: A beginner's questions

On Wed, 2008-01-30 at 18:04 +0100, Luud Heck wrote:
> Hi all,
> 
> I'm new to this list and color management in general so please forgive
> my ignorance and lack of experience here and there. I try to read as
> much as I can in order to avoid wasting your time, but a few nudges in
> the right direction might prove very valuable to me.

Don't be embarrassed.  I've mastered some pretty involved subjects in my
life, e.g., Linux system administration. but I've found color managment
to be one of the most confusing.

> 
> Based on the information I found on the Argyll CMS webpages I obtained
> a Spyder2Express to calibrate and profile my monitor. (Maybe I should
> have looked in the list archives earlier as I read ColorVision is not
> all that Linux friendly, but then again this one is readily available
> in the shops here in The Netherlands which helps if you ask it as a
> birthday present ;-).
> 
> So far I manged to get it working with my Gentoo installation. I used
> the binaries of the latest beta 8 with which it proved very easy to
> get the hardware working.
> 
> However, I'm not sure the profile I generated on Linux is proper. I
> like the colors much more, but the darker areas become really dark.
> Also, the profile I generated on windows with the software from
> ColorVision keeps the images much lighter (to be honest, on windows I
> did not really see the changes before and after calibration which
> worries me a bit as well, but my main interest is in getting it right
> with Linux).

I've profiled my monitor with an Eye One Display under Fedora Core 7
Linux using argyll  and under Windows XP with the vendor's software.   I
haven't compared them directly with screendumps, but under comparable
circumstances, the images I see on my screen look the same.

> 
> A screendump of twice the same photo can be found at the link below,
> on the left displayed with gthumb without color management, on the
> right with the Gimp with a profile generated with Argyll.
> 
> http://www.heck.dds.nl/Comparison-color-management.jpg
> 
> I have a Samsung Syncmaster 191T TFT screen (about 4 years old now)
> and an ATI Radeon 9700Pro graphics card. I need to use the
> fglrx_xgamma program to adjust the gamma of the display (xgamma and
> dispwin did not appear to change anything on my display). 

You shouldn't be using xgamma. You want to load the vgct tag in your
monitor profile using either dispwin or xcalib.   If you look at the
argyll archives you will find an explanation of the difference between
xgamma and the others.  You will also find a discussion I initiated
about  what the point of loading the vgct tag is and what else a color
managed application like gimp 2.4 does with the profile.  I was rather
confused about the matter, and a couple of kindly souls set me straight.

> As my
> monitor is connected via DVI digital I only have backlight control on
> the monitor. I adjusted the gamma until dispcal would tell me that it
> measures a gamma of about 2.2 (using "dispcal -yl -r"). After this I
> ran the profiling step (option 6 when running "dispcal -v2 -yl -o
> Samsung191T").

I have a Samsung 226CW.  You should read very carefully what the argyll
documentation says about profiling LCD monitors.   Lars has addressed
this issue in his answer and you would do well to take his advice.

If you want a valid comparison under Windows, you should leave the
hardware settings on the monitor alone and just let the vendor's
software create the profile.


> 
> $ dispcal -v2 -yl -o Samsung191T
> 
> I read somewhere in the mailing list archive that the option -k0 might
> help, but it made no visible difference in the end result.
> 
> For me the first step is to make sure that what I see on my monitor
> matches with what I would get back from a photo printer service.
> Locally there is one here that provides the icc profile of their
> printing machine for proofing at home.

I suggest strongly that you read a book like Real World Color Management
by Fraser, et. al.  You will learn that you can only go too far in
having your prints match what you see on the screen.  There are first of
all gamut and rendering issues, and also viewing a paper print is very
different from viewing a monitor.  So don't expect miracles.

You will also find ways in such a book to judge the accuracy of your
monitor profile which don't depend on using a print profile to make
prints.  I don't think you should mix up the issues of profiling your
monitor and profiling a printer.  Also, there is a difference between
using a profile for printing and using a profile for proofing. Since I
haven't yet mastered this aspect of the subject, I will leave it for
someone else to comment.

> 
> Now the questions:
> - Is the behavior in the dark areas (bottom left water area for
> example) proper behavior? (If as a test I crank up gamma with
> fglrx_xgamma I can lighten up these dark areas and make the details
> visible again, but the rest of the picture gets way too light then)
>  - What are the best steps to validate what I see on my screen
> compares to the prints (I don't mind ordering prints for testing
> purposes, but prefer to use the right methods for this as not to waste
> too much money on going back and forth)


>  - Are the steps I took proper or did I miss something?
> 
> Thanks for your time and patience,
> Luud Heck

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