RGB to CMYK Conversion

[Cap'n Fishy]

Once a year I need to convert some images from RGB to CMYK for printing purposes. I am doing it in PS using <Edit> <Convert to Profile>. Most don't change to any significant extent in the conversion, but the odd one goes really naff, with a lot of loss of saturation of certain colours. That is why I started doing it myself - in the past I left it to the printer, and got some nasty surprises with what I got back.

This time round it is one image with lilac hues that have gone dull and muddy. I have tried mucking about in PS adjustments, eg with saturation and lightness of individual colours, but it either doesn't help, or it introduces artefacts.

Any ideas?

Col

 

[GardenersHelper]

Looking where lilac is on the CYMK vs "monitor" vs Pantone diagram here, and the associated text, could it be that your lilac is out of gamut for CYMK?

(I would guess that their "monitor" gamut is sRGB, but it is only a guess.)

EDIT: this diagram is a bit clearer.

 

[Cap'n Fishy]

Looking where lilac is on the CYMK vs "monitor" vs Pantone diagram here, and the associated text, could it be that your lilac is out of gamut for CYMK?

Aye, that's it. I did a bit investigation. I have an inkjet, which needless to say prints in CMYK. I took the original in RGB with the nice vibrant lilacs and set up a print job with it, and then clicked the gamut warning. Sure enough, it flagged the whole area where the lilacs were. I printed it to see. Dull as ditchwater! Then I converted the file to CMYK. It went dull, and when I set up the print job and clicked the gamut warning, there was no flagging - as it had already thrown out all the colours it couldn't print. I printed 3 versions: sRGB, Adobe RGB and CMYK. Not a ha'p'th of difference between any of them!

So, how can you print lilac?

Col

 

[GardenersHelper]

Aye, that's it. I did a bit investigation. I have an inkjet, which needless to say prints in CMYK. I took the original in RGB with the nice vibrant lilacs and set up a print job with it, and then clicked the gamut warning. Sure enough, it flagged the whole area where the lilacs were. I printed it to see. Dull as ditchwater! Then I converted the file to CMYK. It went dull, and when I set up the print job and clicked the gamut warning, there was no flagging - as it had already thrown out all the colours it couldn't print. I printed 3 versions: sRGB, Adobe RGB and CMYK. Not a ha'p'th of difference between any of them!

That makes sense. Unfortunately. (I have colour rendering issues too - some greens as well as some purple/lilac colours. I'm thinking that some of this is probably gamut issues, but separating that out from imperfections in my techniques, colour perception and memory, screen, screen calibration etc is distinctly non-trivial.)

So, how can you print lilac?

Perhaps there are some commercial printers that print wider gamuts. Don't know. I just did a quick bit of searching, but didn't find any reference to wider-gamut printing services.

I keep reading that modern ink-jet printers have wider gamuts, but I've had no luck yet (again, only some quick searches) in finding out the gamut for any particular printer.

This post hints that even the wider printer gamuts may not be an answer to every prayer in this area. I haven't read the whole thread, but one of the subsequent posts links to this tutorial at cambridgeincolour - it all gets a bit complicated.

I'm currently trying to work out whether to get a wide gamut monitor. It might mean I could make images with better (more accurate, more discriminating, more detailed) colour rendition for my own viewing, but I'd then have the complication of translating to sRGB for Internet use, and as for printing ??? Not sure the complications would be worthwhile.

Perhaps stick with sRGB but start using the soft proofing in Lightroom 4 (I'm a new Lightroom user, and I haven't looked at that part of Lightroom yet). According to an Adobe video I watched this lets you see what is out of gamut for particular output devices, and presents those area as selections which you can then change to in-gamut values. Not the same as getting the colour you really wanted, but it does give some control back in terms of not losing so much detail, apparently.

 

[GardenersHelper]

I just had a first look at Lightroom's soft proofing. I started looking at some of the pictures I captured today in the garden. I didn't have to look far to find gamut issues.

Here is an example. I have turned up the temperature to make the problem areas bigger and easier to see, but the issues are still there at a more "proper" temperature, just not so much so. The (raw) image is unprocessed apart from the temperature change and Lightroom's standard input noise reduction and input sharpening.

This is what the image looks like using the sRGB gamut.


Lightroom 4 soft proofing Perceptual sRGB by gardenersassistant, on Flickr

Here is what it looks like using the profile for the Fuji Frontier printer used by the commercial printer I use (DSCL).


Lightroom 4 soft proofing Perceptual Fuji Frontier Printer by gardenersassistant, on Flickr

Here is what I got when I turned the gamut warnings on.


Lightroom 4 soft proofing Perceptual gamut warnings by gardenersassistant, on Flickr

The red areas are the Destination (Fuji printer) warnings. These are all to do with pink colours in the image.

The blue areas are the Monitor warnings. These are all to do with green areas.

In the next screen capture, on the panel on the right hand side you can see some reductions in saturation I made which brought the image back into both the monitor and printer gamuts. Bringing the Red saturation down brought the image back into the printer gamut. To get the greens back into the monitor gamut I first reduced the Green saturation. I had to turn down the Yellow saturation a bit to finish off the job.

I was interested to see that turning the Red luminance down made the printer gamut problem worse. Turning the Yellow luminance down made the monitor gamut problem worse for the little, yellower green in the centre of the flower. Changing the Green luminance in either direction seemed to make the green gamut problem shift around to different areas, but not obviously better or worse in terms of the amount of it.

Lightroom 4 soft proofing Perceptual saturation adjustments by gardenersassistant, on Flickr

 

[Chappers]

Colin

Are you looking at having the image printed via Litho printing or is it more of an ink jet printer you are after.

Next question, have you looked at soft proofing the file as an RGB one and seeing which of the standard colour spaces, sRGB Adobe RGB etc gives a better representation of the lilac colour?

John C

 

[Cap'n Fishy]

Colin

Are you looking at having the image printed via Litho printing or is it more of an ink jet printer you are after.

Next question, have you looked at soft proofing the file as an RGB one and seeing which of the standard colour spaces, sRGB Adobe RGB etc gives a better representation of the lilac colour?

John C

It's actually going off to a commercial printer for a calendar. I don't know what his gear is, but I know he converts to CMYK, and so to ease the pain, I do the conversion before I send them off, so I can see how much damage there is and I at least have a chance to make a few tweaks or even ditch the image if it is too bad.

It's a strange one, as I have done plenty printing on my deskjet over the years, and plenty other stuff - magazines, greetings cards, reproduction onto products and so on, and I have never been aware of this issue - I maybe have been lucky or maybe it is something about the ones I tend to pick for the calendar that brings out the 'gamut gambler' in me?

I'm guessing this is why the printer manufacturers have over the years been increasing the number of inks - adding red and green and so on? But then you would think a commercial printer should be up to speed on this. And if you are proofing it in Photoshop, how do you tell PS, "Aye, it's CMYK, but it's got red and green as well, so it's really CMYKRG. Show me that one!"

Col