I have always been a fan of a product that solves a problem, but what if people don’t even know they have a problem. Then I guess it’s my duty to tell them the bad news and explain how to solve it. Ok, I know that sounds a bit pompous, but let me explain before you turn the page.
CMYK colour is made with various recipes and not every colour recipe is ideal for every printing condition. It would be so much easier if we only had one printing condition and could convert all our files into the single CMYK destination colour space. But that’s not an option at this point. If we look at the offset/litho printing industry we have a few popular options. The top three in order of popularity seem to be: U.S. Web Coated (SWOP) v2, GRACoL_Coated1v2 and U.S. Sheetfed Coated v2. The problem is that each one of these recipes will look the same on the screen BUT will print differently.
I hope the example below proves the point. The three images were converted from RGB to the three labeled colour spaces. Onscreen each one looked the same, as they should. Then I combined the three images into one Photoshop document and when doing so I selected “Don’t convert (preserve color numbers)”. This way the three images would keep their original CMYK numbers.
We see small differences between the three images. It is not about one looking better. It is that we have learned that a document’s CMYK recipe plays a big part.
So what do I mean by colour recipes? The CMYK colour space is device-dependent. This means that when you convert from a standard RGB colour space such as Adobe RGB that is not device dependent, to a CMYK colour space such as SWOP, you have made a decision about a number of variables that will influence the outcome. Things like total ink limit, the amount of GCR, when and how the black plate is used to build the neutrals and also how the near-neutral colours such as browns and shadows are created.
But what happens when you are a printer and the supplied PDF has multiple pages and you have no idea how any of the images were created? Some images could predate the use of colour management and could be using older separation tables to create the CMYK image.
And this is the problem — a problem you didn’t know you had. What you do know is that at times it is tough to match some jobs to your calibrated proof and other times it is not. The challenging images are usually browns, pastels and areas with a lot of coverage. Could this be because some images are not properly converted to the colour space of your press? Yes!
A lot of people, including myself, were not aware or though it made little difference if images were in the same colour space as your proofing RIP or your press. I thought that CMYK was CMYK and it would just work out. Well I was wrong.
Up until recently we had no easy way to harmonize all the CMYK images in a PDF. But it would not be fair of me to tell you of a problem when there is no solution. The solution is a colour server – a piece of software that converts all the images in a PDF into your required or desired CMYK colour space. Best of all it does this without changing the colour of the image. This last sentence is an important one, so I will say it again. This CMYK to CMYK conversion does not change the colour of the image, it merely changes the values to be in line with what your press is expecting. Now all the images on the page will be in the same colour space so you can have more predictable colour.
Lots of companies are selling ICC colour servers. A quick Google search with “ICC color server” will bring up a few.