[Digikam-users] Canon Color profile testing

[Gilles Caulier]

On Wednesday 06 December 2006 23:00, Daniel Bauer wrote:
> Hello everybody
>
> experimenting with colors... I have tested many different profiles, but I
> am still not happy with the results I get.
>
> As much as I can see there are two possibilities:
> 1) the Canon camera profiles we have are not really usable, or

You need to use the right camera profile, fully compatible with the RAW linear 
image resulting of dcraw conversion (16 bits color depth). More info here 
abour RAW linear picture here :

http://www.aim-dtp.net/aim/techniques

To use the right Canon/Nikon camera ICC profiles fully compatible with 
digiKam, i recommend hightly to use LightZone profiles. This program, 
available for linux use internally dcraw 8.31. I'm sure, i have checked the 
content of java tarball.

I have extracted for you the icc color profiles :

http://digikam3rdparty.free.fr/ICCPROFILES/CameraProfiles/LZ.2.0/

> 2) I am just too stupid to achieve good results.

no (:=), but the ICC color profile is not the only piece of RAW workflow. It 
more complicated. Let's me explain better with an example...

>
> I hope it's no. 1 :-)
>
> I guess Canon camersas are quite widely used. So if you are interested in
> doing some tests, I have a sample picture* for you on my server:
>
> - the unchanged original picture from camera Canon EOS 20D:
> http://www.daniel-bauer.com/test/IMG_0048.CR2 (7.1 MB)
>
> - the 16-bit tiff, the same picture converted to "wide gamut" with embeded
> profile, made with Canon Digital Photo Professional on Win98. No
> corrections have been applied:
> http://www.daniel-bauer.com/test/IMG_0048.TIF (46.9 MB)
>
> - the 16-bit tiff  converted from wide-gamut-tiff to Adobe-SRGB-Tiff with
> photoshop. This "final" version is as the picture should be in the end:
> http://www.daniel-bauer.com/test/IMG_0048_photoshop.tif (46.8 MB)
>
> Using digiKam to convert the wide-gamut-tiff to adobe-srg-tiff works
> perfect, gives quite the same result as photoshop.

It's normal. It just to change color space. The method is the same between 
photoshop and digiKam. Of course, Internally digiKam use LCMS library and 
photoshop an internal framework. But the method is normalized, and this is 
why the result are the same.

>
> But the most important first step: converting from Original CR2 to
> wide-gamut (or directly to SRGB) just doesn't give any good results with
> digiKam, no matter how I try. I think this is because we don't have really
> good profiles for Canon???

no. because the profile is not the only one transformation to have the right 
result. Look here :

http://digikam3rdparty.free.fr/Screenshots/CR2RAWImport/CR2importInImageEditor.png

.. in this screenshot, you can see on the middle the Color Management plugin 
in action working on your CR2 picture to import RW file in editor. On the 
right showfoto have open your TIF WideGamut file generated by Canaon soft. We 
will compare result with both windows.

Note: of course in digiKam CM is enable and i'm decoding RAW files in 16 bits 
color depth. 

Now we back to the color management plugin. We need to adjust some settings to 
complete import in editor, especially the right camera profile from 
LightZone :

http://digikam3rdparty.free.fr/Screenshots/CR2RAWImport/InputProfile.png

... the workspace color profile :

http://digikam3rdparty.free.fr/Screenshots/CR2RAWImport/WorkspaceProfile.png

... and the lightness adjustement :

http://digikam3rdparty.free.fr/Screenshots/CR2RAWImport/LightnessAdjust.png

This point is _very_ important : Canon, phtoshop, ufraw, lightzone used a lot 
of Exif makernote provided by camera in picture to adjust automaticly this 
settings. digiKam do nothing like this yet. It's a piece of code to do and 
it's planed to later (:=)))... This is want mean than _you_ must need to do 
it by hand.

After to set all adjustments, the import is complete :

http://digikam3rdparty.free.fr/Screenshots/CR2RAWImport/CR2ImportDone.png

Note : You can see a difference between Canon import and digiKam import 
especially in highlight (look the wall light behind the chair). You can see 
the problem in high value of histogram.

Personally, thing than the digiKam import is better because the highlight are 
not overexposed. I suspect a wrong setting in Canon soft perhaps the gamma 
adjustment.

At this point there is 2 schools : set a full auto import, or a by hand 
import. I prefer the second one, because when i shoot pictures in RAW, i will 
work indeep all adjustements. If i want a full auto picture, JPEG is perfect.
This is why auto-adjustment like UFRAW is not yet done in digiKam (:=)))...

Ok, now we continue. Here we have the sRGB transform. On the middle the 
digiKam image editor, on the right Showfoto with sRGB file generated by 
photoshop :

http://digikam3rdparty.free.fr/Screenshots/CR2RAWImport/ConvertTosRGB.png

There is a difference between both image. This is is due to the first stage of 
course, when we have imported the image from CR2 in wide gammut color space. 
We can correct a little this point using Color correction Image Editor tools 
like White Balance :

http://digikam3rdparty.free.fr/Screenshots/CR2RAWImport/WBAdjust.png

... like this :

http://digikam3rdparty.free.fr/Screenshots/CR2RAWImport/sRGBFinal.png

It's not optimum, but the image is pleasant to read. The Photoshop sRGB is too 
cold i think (it's my viewpoint of course (:=)))).

To close my report, look the comparison between digiKam sRGB and LightZone 
sRGB :

http://digikam3rdparty.free.fr/Screenshots/CR2RAWImport/sRGBdigiKamvsLightZone.png

...It's the same. Normal, LightZone and digiKam use the same ICC camera 
profile. The only difference is than LightZone adjust automaticly Lightness 
correction and digiKam no.

Gilles