- Less than 5MB
- "CMNJ" which I found is the french for "CMYK colors"
- JPEG hi-def
It took me some time to find the appropriate tools for Ubuntu Linux, since Gimp was not much help with all that. CMYK seemed to be planned for the Gimp-v3.0, but all I found were comment on this "future release" (I'm now using "GNU Image Manipulation Program version 2.6.11", standard one with Ubuntu...).
DPI problem
I used the XnView tool to reset the DPI to 300.
xnview : (sudo apt-get install xnview was enough to install it !)
I found this tool following what is explained here : http://www.rideau-info.com/photos/changedpi.html.
CMYK problem
First of all, I had never heard about it, so I was gonna assume it was the default format... In French CMYK is called CMJN, and referred as "Quadrichromie" (opposed to "RGB"(en) "RVB"(fr) "trichromie").
Of course, the pictures I had were in RGB, so I had to convert them to CMYK.
I found a tool able to do that easily, coming on the side of the LittleCMS image library : jpegicc !
Hoping my quest was over, I read the doc on how to use it, and found that CMYK needed some "profiles definition". Looking around on the net, I found some distributed by Adobe doing a search on their website "research" tool. I then found a .zip, unpacked it and had RGB and CMYK profiles (~10 differents).
In order to test them, I applied all of them (in the folder "profiles/CMYK_Profiles/" ) to a sample file "test2.jpg" to see the resulting colors :
for i in profiles/CMYK_Profiles/* ; do jpegicc -o"$i" test2.jpg test2.cmyk--`basename "$i"`.jpg ; done
To the lazy ones, the command for a single profile (or to copy-past it) :
jpegicc -oProfile.icc file-In-RGB.jpeg file-Out-CMYK.jpeg
Those were rendering quite different colors at the end, and I said good bye to my white background.
