ps2pdf: preserving cmyk

[H.S.Rai]

I am to convert PostScript file (having images in CMYK) to pdf. I
found conversion ps2pdf make images in RGB mode. Many options were
tried, but could not succeed.

Can anyone know sure shot method to do this with preserving CMYK mode,
and / or controlling dpi of images.

There is requirement:

1) For screen view: Images in RGB, resolution 100dpi
2) For Print: Images in CYMK, resolution 300 dpi.

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H.S.Rai