JPEG to CMYK conversion issue?

[zazarb]

Hello,

Sorry if the question is obvious but I am new to CMYK conversion.

I have just tried to use NConvert to convert RGB Jpeg files to CMYK jpeg files, with a 300 dpi resolution (the original images have a 72dpi resolution):
nconvert -o output_file -out jpeg -dpi 300 -cmyk_space *.*

This command fails because my resulting jpeg images have a 72 resolution dpi (i.e. the resolution is not set to 300 dpi during the conversion)

When I do the exact same thing, but I convert the RGB Jpeg files to CMYK tiff or pdf files instead, everything works well (i.e. my result images have a 300 dpi resolution)
nconvert -o output_file -out tiff -dpi 300 -cmyk_space *.*

I have been trying to understand why it works with pdf/tiff format but not Jpeg format, can somebody explain this to me?

Thanks for your help

[zazarb]

[update] Actually the conversion to JPEG => CMYK pdf with 300 DPI also fails. I only succeed in gettying CMYK color space + 300 dpi by converting to TIFF
Thanks

[xnview]

-dpi is only used for pdf, if you want to resize your picture use

Code: Select all

-resize

[Koniec12]

DPI is used generally for graphics not only pdf