Best results when changing RGB to CMYK

@crispincorky ::WORKING IN OR CONVERTING RGB TO CMYK::

Generally I would advise that there is significant opportunity for error when converting to CMYK unless some thought is applied to the process.

When simply choosing image>mode>cmyk the default CMYK ICC default profile [as selected in "Color Settings"] is used. IF that default profile relates properly to the print condition that’s the destination for the files then that's OK.  [usually CMYK data is prepared for an offset or digital press].

BUT, many users simply take the advice to use image>mode>cmyk without checking whether the default CMYK ICC profile is the right one for the print destination in question. That can lead to some pretty unsuitable data going to press and, thus, a disappointing print run.  

::INKJET PRINTING::

Unless preparing files for an inkjet winter driven / controlled by a RIP, then the pipeline that’s used for the data converts from CMYK back to "whoknowswhat" RGB before printing. ALL inkjet printers I know of, unless RIP driven, are far better treated as RGB devices. Taking data from RGB via a press CMYK might needlessly reduce colour gamut - so, will potentially reduce saturation in areas that could have been fully realised had RGB data been sent to the printer driver software. Inkjet printers tend to have colourspaces that far exceed the CMYK press ICC profiles installed with Photoshop

I hope this helps explain my position on working in CMYK colourpace 
neil barstow, colourmanagement net - adobe forum volunteer - co-author: 'getting colour right'
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Hi Test Screen Name,

That’s a point, in RIP conversion - and it often works fine.

In fact it's the default process of a modern "late binding"workflow where the PDFs are made in RGB and conversion to CMYK is automated down the line based on printing use.

However, I like to teach my clients (many of whom are photographers) that’s its worthwhile taking control of the conversion from RGB to CMYK manually, creatively, on a file by file basis.

- That way the colour and tonal compression issues sometimes associated with conversion to CMYK are often avoided, such as the dreadful purple skies we've all seen in print. A bit of judicial editing to saturation of severely out of gamut colours in the RGB file can often smooth an image's way through the conversion to CMYK and into the world of offset print.

Also choosing between relative Colorimetric and Perceptual Rendering Intents for CMYK conversions can improve results,

there is no sensible overall default for Rendering Intent.

Even if a photographer or designer is going to send out an RGB file in the end, it can still be worth doing the above judicial edits to saturation [as preview to it's eventual conversion] to ease the images way through the bottleneck en route to offset print.

I hope this helps

if so, please do mark my reply as "helpful"

thanks

neil barstow, colourmanagement

Sorry,

I am sure your comment was well intentioned but I am afraid you are mis-informed -

For the safety of other users, I feel I need to point out that the method you describe is a really simplistic and possibly even dangerous method of converting from RGB to CMYK

And its pretty rare that a conversion to CMYK will  happen "without losing any colors" which you claim to be the result of using your "easy" method.

Why is Photoshop's  "image/mode/CMYK" too simplistic?

- because relies upon 2 settings which a user may have never even looked at:

1: the default CMYK profile selected in Photoshop's "color settings".

This is often not the right CMYK profile for the current print job.

CMYK profiles are totally specific to the print method and substrate, there are NO good defaults w that work for everything.

e.g such conditions as Coated or uncoated paper - sheet fed or web press or even newsprint perhaps?

you can read more here: color management / colormanagement : about icc colour profiles

When sending a letter you'd never use a default ZIP code, do remember that CMYK needs the right coding too.

2: the default rendering intent in Photoshop's "color settings".

Controlling the rendering intent during conversion can provide better results that relying upon a default.

in Photoshop's "convert to profile" action is the safe way to do this conversion.

I hope this helps

if so, please do mark my reply as "helpful", so others who have similar issues can see the solution

thanks

neil barstow, colourmanagement

What if your client is unable to get the print details from the print house or is reluctant to give you the contact details of the print house directly (goodness knows why!), how on earth do you know whether to leave the images as RGB or change them to CMYK, I am worried that if I leave the images as RGB for the print house to sort out and the print house don't think to change them to CMYK the end result will be awful?

I have this same trouble with trying to get the PDF spec from some print houses, it's like pulling teeth, I am going to have this issue with this current job too if I cannot get hold of the print house's contact details. I just want to make sure I set the artwork up as best I can for the best results.

can you show me how to do that please