I am trying to generate an RGB thumbnail for a CMYK pdf file using the Dragonfly gem. It is working fine with this code:
file.image.convert("-flatten -density 300 -quality 100", 'format' => 'jpg', 'frame' => 0).url
The result is the correct url of the thumbnail image.
Since some users upload CMYK documents, I want to convert them using color profiles and the colorspace
option:
file.image.convert("-flatten -profile /path_to/USWebCoatedSWOP.icc -profile /path_to/AppleRGB.icc -colorspace rgb -density 300 -quality 100", 'format' => 'jpg', 'frame' => 0).url
The result is always "nil". No error is shown.
When I execute the code (which is shown in the console) manually in the terminal, the file is correctly converted. The "DRAGONFLY: shell command":
convert /path_to/my_cmyk_file.pdf[0] -flatten -profile /path_to/USWebCoatedSWOP.icc -profile /path_to/AppleRGB.icc -colorspace RGB -density 300 -quality 100 /path_to/my_rgb_thumbnail.jpg
The result is this:
/path_to/USWebCoatedSWOP.icc ICC 1x1 1x1+0+0 16-bit sRGB 557168B 0.010u 0:00.000
/path_to/AppleRGB.icc ICC 1x1 1x1+0+0 16-bit sRGB 552B 0.000u 0:00.000
/path_to/my_cmyk_file.pdf[0]=>/path_to/my_rgb_thumbnail.jpg PDF 420x595 420x595+0+0 16-bit sRGB 56625B 0.180u 0:00.190
What could cause the problem within Dragonfly?
I managed to get it to work with a custom processor and the shell_update
functionality:
processor :cmyk_pdf_thumb do |content|
content.shell_update ext: 'jpg' do |old_path, new_path|
"convert -density 300 #{old_path}[0] -flatten -profile USWebCoatedSWOP.icc -profile AppleRGB.icc #{new_path}"
end
end
Now I can convert CMYK documents by file.image.cmyk_pdf_thumb
. Even if I set the ext
option to "jpg", I have to encode
the result to get a JPEG file:
file.image.cmyk_pdf_thumb.encode('jpg').url