RGB and CMYK import to PM 1

[tisnix108]

I received some images on CD-rom (CMYK),
others I scan (RGB)
I work them in Photoshop, sometimes I use a filter:
to use a filter I convert to RGB.
Do I need to reconvert to CMYK before saving the image to my PM-file?
(this gives pixelation on the filters I used)
Convertion to CMYK is 'separation' which should be done at the end of the process yes?

 

[carlow]

Hi

It depends on what you are going to do with your images. if you are going to use them in a document that will be printed, than you must make the conversion.

If you are going to use them for the web all images must be RGB.

never mix up cmyk and rgb in a document, when you do you're asking for trouble

..)
grillhouse

 

[zefir]

Tisnix: PM works well with RGB images for desktop printers.
For offset printing the linked images should be CMYK.
The RGB-CMYK conversion in Photoshop requires the correct
press profile.
An RGB-CMYK conversion cannot be reversed without severe losses.
It´s so far not the separation (= split into 4 separate layers for 4 B/W films).
My way for offset printing: test the RGB-CMYK conversion
in PhS by use of standard profiles (SWOP, Euro...).
Modify RGB-Copy until good results are achieved.
Give the Service Bureau the modified RGB-Copies and let them
convert, using their own profiles.
Import (link) of CMYK in PM requires the Color Management
System = On, and correct parameter settings.
Hope this helps. --G.Hoffmann.

 

[tisnix108]

Yes Grillhouse,
These questions were about printing documents exclusively,
so : -never mix up- rgb and cmyk in a document!
neighter in document PM for printing (= always CMYK)
nor for the web (= always RGB).

To Zefir,
Yes, the loss by RGB-CMYK conversion
cannot be repared,
"For offset printing the linked images should be CMYK."
you state, (corresponds with what Grillhouse says)
but +
a)test the RGB-CMYK conversion (in Photoshop)
b)give the Service Bureau the modified RGB-Copies,
=
convert to CMYK + give the Service Bureau modified RGB-copies?(not linked)
please specify Zefir

thanks for your advice, :-0

tisnix108

 

[zefir]

Tisnix: even if you optimize your RGB-copies by a slightly wrong
press profile (like Euro.. instead of SWOP) you will become
familiar with the limitations of CMYK printing.
E.g. PhS can give you the so called "Gamut Warning".
This shows the pixels which cannot be represented reasonably
in the CMYK print.
Then make your PM file as usual and link the optimized RGB-copies.
"Link" means: point to the image files, but don´t include them in the
PM file.
Save for Service Provider can copy the PM files and all linked images
into one folder, but this can be done also manually.
My work flow: The SP can make the RGB-CMY conversion much better
than I , because I don´t know all the details, like his press profile,
dot gain, undercolor removal. E.g. the dot gain depends on the paper.
The trials in advance will create RGBs, which are convertible with
nearly no problems.
Professionals are of course able to deliver the final CMYKs, but this
needs a lot of coordination with the SP.
Please feel free to ask for further explanations. I make sometimes
brochures, not daily. ---G.Hoffmann

 

[tisnix108]

Thank Zefir,
tisnix108

 

[zefir]

Thanks for the feedback. ---G.Hoffmann