[Digikam-users] Color management behaviour

Fri Jun 19 18:05:35 BST 2009

Hi Leonardo,

I'm quite a newbie on color management, but I'll try to describe my setup and 
workflow in the hope it helps you.

I'm using an EOS 450D and digiKam 0.10.0 on openSuSE 11.1. The first thing 
with CR2 files is that they don't have an embedded or built-in color profile.

But, we need to tell digiKam which is the camera profile. I've been wandering 
a while with Digital Photo Professional (the raw converter/editor supplied by 
Canon). At least in mine, the camera profiles can be found under the folder

C:\Program Files\Canon\Digital Photo Professional\icc

There are in fact a pair of ICC profiles, one for sRGB color space and one for 
AdobeRGB color space, for each picture style available

Faithful: fs.icc, fa.icc
Landscape: ls.icc, la.icc
Neutral: ns.icc, na.icc
Standard: ss.icc, sa.icc
Portrait: ps.icc, pa.icc

So if you work with sRGB colorspace, the suitable camera profiles should be 
fs.icc, ls.icc, ns.icc (*s.icc for sRGB), and so on. Copy them to 
/usr/share/color/icc under Linux and configure the path and preferred input 
profile on the Color Settings setup tab. These profiles are *not* identical to 
standard sRGB or Adobe RGB, they are specific to the camera model. This can be 
the reason you see the picture differently with/without color management.

As for the monitor profile, monitors come frequently with a "driver" in CD, 
part of which is the monitor's color profile. For example, I own an LG Flatron 
(not quite a good display as I would be pleased to have ;-) ). I searched on 
the driver CD and found the file lh1970hr.icm, which is the display profile 
for this particular model. As before, I copied this file to 
/usr/share/color/icc and selected it in digiKam setup. And as before, the 
monitor's profile is *not* identical to standard sRGB (although approximate), 
it is specific to the display model.

On the other hand, a distinction must be made between profiling and 
calibrating a monitor. Both are **essential** to have a good, or at least 
acceptable, color-managed workflow; otherwise you'll get under/overexposures 
while adjusting, as well as color shifts/casts. So in addition to getting a 
good monitor profile, you need to calibrate as much accurately as you can the 
monitor's black point, white point, and gamma. I suggest the methods described 
in the excellent tutorials and charts from Norman Koren at

http://www.normankoren.com/makingfineprints1A.html

which, if you don't need an extreme color accuracy, can be done "eyeball" 
without the need of a spectrometer.

Personally I always shot RAW in Adobe RGB colorspace, as it is a bit wider 
than sRGB and well suited for editing / printing. On the RAW converter I 
select the Landscape Adobe RGB input profile (la.icc) for general use, but 
change it when appropiate (pa.icc for portraits for example).

Once finished editing, I select Color -> Color Management, set Input Profile = 
Embedded profile, Workspace profile = sRGB and click OK to convert from Adobe 
to sRGB. Then I save the finished image in JPG or PNG format with sRGB 
embedded in it. In this way I see the picture OK in digiKam as well as in 
Gwenview or the GIMP.

Maybe the camera profiles are different for your 350D, but you can install 
Digital Photo Professional in a Windoze box, and use the filemon.exe utility 
from Micro$oft

http://technet.microsoft.com/en-us/sysinternals/bb896642.aspx

to investigate which files are opened/used during conversion and editing. One 
or more of them will be the camera profiles :-)

Wow, sorry for the length ;-)  I hope that if something is wrong the "gurus" 
will reply with the truth (don't forget I'm also a newbie :-)), simply it 
works quite well for me.

Regards,

Francisco

On Viernes, 19 de Junio de 2009, Leonardo  wrote:
Hi all,

I'm definitely lost with color management, I'm experiencing a number of issues 
(which I'm going to describe) and I do not understand where (if)
I'm doing something wrong.

I'm using digiKam 0.10.0 on Kubuntu Jaunty.

I refer to some screenshots you can find on Picasa ath the following address: 
sorry for the localized interface.

http://picasaweb.google.it/giordani.leonardo/DigiKam0100KubuntuJaunty#

My color management settings are:

Monitor: eye-made profile built with lprof (Samsung SyncMaster) - it is 
identical to an sRGB profile
Workspace: sRGB (since my monitor is limited)
Input: Canon Profile
Rendering: Perceptual

Since screenshots describe my workflow I'll comment them all.

01. First I start with a RAW file (.CR2) made by my Canon EOS 350D

02. I open it in Image Editor and digiKam ask me about "convert" or "assign" 
to current workspace profile (sRGB): since the source image is RAW
I choose "convert".

03. Here is my picture: it is a bit dark since the histogram (not shown in the 
screenshot, sorry) is concentrated on low keys.

04. If I try to deactivate color management (with the small bottom right icon) 
I obtain a picture with a brown look. You can see it on screenshot
number 09, where I compared the two side-by-side.

Question 1: why, if my monitor has am sRGB-like profile, does the picture 
change when I activate/deactivate color management?

05. After some work I obtain the final picture.

06. I save it as JPEG (aiming for example to Web publishing) and the small 
preview on the left side of the screen looks different, just like the
picture with color management deactivated.

07. When I close Image Editor I see that the preview of my JPEG has that brown 
look I did not have in Image Editor; the same happens with Gwenview or
any other image viewer. If I open it with The Gimp it says "The image has a 
color profile (sRGB), convert to sRGB built-in?". Both converting and letting
the original profile result in a correct image.

Question 2: why, if the built-in profile is the common sRGB, digiKam, Gwenview 
and others do not see it correctly? Why Gimp can? I understand that an
application cannot implement Color Management, but this is an sRGB profile, 
the "de-facto" standard when no color management is active. Or not?

08. If I try to open the JPEG with digiKam it keeps asking me if I want to 
convert or assign the sRGB color profile.

Question 3: why does digiKam not recognize the built in profile?

10. Now I try to deactivate color management. Picture in Image Editor looks 
different (understandable, without camera profile).

11. After some work I end up with a picture that, when saved, viewed with 
Gwenview, Gimp or whatever, is always identical.

Question 4: why now every application can see my picture correctly? I tried to 
move them on my laptop, which has a poor monitor, and I can barely see
the differences with my main monitor both in the color-managed picture and in 
the other one.

Thank you very much in advance for your answers, and thank you for digiKam

Leonardo

> Hi all,
>
> I'm definitely lost with color management, I'm experiencing a number of
> issues (which I'm going to describe) and I do not understand where (if) I'm
> doing something wrong.
>
> I'm using digiKam 0.10.0 on Kubuntu Jaunty.
>
> I refer to some screenshots you can find on Picasa ath the following
> address: sorry for the localized interface.
>
> http://picasaweb.google.it/giordani.leonardo/DigiKam0100KubuntuJaunty#
>
> My color management settings are:
>
> Monitor: eye-made profile built with lprof (Samsung SyncMaster) - it is
> identical to an sRGB profile Workspace: sRGB (since my monitor is limited)
> Input: Canon Profile
> Rendering: Perceptual
>
> Since screenshots describe my workflow I'll comment them all.
>
> 01. First I start with a RAW file (.CR2) made by my Canon EOS 350D
>
> 02. I open it in Image Editor and digiKam ask me about "convert" or
> "assign" to current workspace profile (sRGB): since the source image is RAW
> I choose "convert".
>
> 03. Here is my picture: it is a bit dark since the histogram (not shown in
> the screenshot, sorry) is concentrated on low keys.
>
> 04. If I try to deactivate color management (with the small bottom right
> icon) I obtain a picture with a brown look. You can see it on screenshot
> number 09, where I compared the two side-by-side.
>
> Question 1: why, if my monitor has am sRGB-like profile, does the picture
> change when I activate/deactivate color management?
>
> 05. After some work I obtain the final picture.
>
> 06. I save it as JPEG (aiming for example to Web publishing) and the small
> preview on the left side of the screen looks different, just like the
> picture with color management deactivated.
>
> 07. When I close Image Editor I see that the preview of my JPEG has that
> brown look I did not have in Image Editor; the same happens with Gwenview
> or any other image viewer. If I open it with The Gimp it says "The image
> has a color profile (sRGB), convert to sRGB built-in?". Both converting and
> letting the original profile result in a correct image.
>
> Question 2: why, if the built-in profile is the common sRGB, digiKam,
> Gwenview and others do not see it correctly? Why Gimp can? I understand
> that an application cannot implement Color Management, but this is an sRGB
> profile, the "de-facto" standard when no color management is active. Or
> not?
>
> 08. If I try to open the JPEG with digiKam it keeps asking me if I want to
> convert or assign the sRGB color profile.
>
> Question 3: why does digiKam not recognize the built in profile?
>
> 10. Now I try to deactivate color management. Picture in Image Editor looks
> different (understandable, without camera profile).
>
> 11. After some work I end up with a picture that, when saved, viewed with
> Gwenview, Gimp or whatever, is always identical.
>
> Question 4: why now every application can see my picture correctly? I tried
> to move them on my laptop, which has a poor monitor, and I can barely see
> the differences with my main monitor both in the color-managed picture and
> in the other one.
>
> Thank you very much in advance for your answers, and thank you for digiKam
>
> Leonardo
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.kde.org/pipermail/digikam-users/attachments/20090619/d724b551/attachment.html>