What colour space?

Lightning Source has stricter requirements for covers on colour interior books and Tom Rath has just completed a new colour edition of his KittenCat book. As I’ve recently mentioned, it was frustrating that the communication back to me of a problem was delayed by a good two weeks and even more frustrating to find that Photoshop Elements apparently will not produce the specifically required flavour of PDF file.

My guess is that the format requirement buries the insistence on the CMYK colour space common to printing rather than RGB which is the space commonly used on the web and on computer screens. CMYK relates to the way light is subtracted as it is absorbed on a piece of paper. C (Cyan) is a sort of light blue, M (Magenta) is a sort of reddish purple, Y (Yellow) is as you would expect and K (blacK) is the absorbing of everything (used in printing so they don’t have to try to mix the other three inks to get black). Even my inkjet printer has 4 ink cartridges…each with one of those colours. Another approach to ptinting is ‘spot colours’ where the printer makes print passes with specific ink colours for specific purposes (like a 2 or 3 colour flyer that does not need to reproduce full colour pictures). Even some of the fancier home ink-jet printers add extra colours like a light cyan to enable them to do a better job on skies and skin tones.  Anyway, the world of print is a very complicated one and ‘speaks’ CMYK.

RGB relates to the way emitted light adds up to make a colour. It was a vital part of the phosphors that went ino a TV screen…there was either a phosphor pattern of 3 dots or 3 vertical bars onthe inside of the glass with a shadow mask behind so the 3 electron beams would land on the right phosphors. The more energy in each of the three beams, the brighter would be that colour at that location as the beams, over and over, swept across the screen. It the beams were shut off at a spot, that was black. If they were all full on then white light came out…only the red beam and the spot looked red…turn on the yellow and it looked orange…and so on. The same principle applies in the flat screen technologies–light is added.

Although I’m not sure of the exact technology these days, digital cameras use sensors to detect the colour of light coming through the lens and the built-in computer chip process that into RGB colour space (and usually compress images into JPEG files. This works just fine for most uses of images…put them on Facebook and share them with family and friends or take them to the local Kiosk and get them printed (any conversion to CMYK is automatically done by their computer). The lower-end Photoshop Elements doesn’t aim for the printing market, so, as best I can tell, they leave out the CMYK stuff…after all, how can they justify the $thousands for the full-blown version if the $100 one did the trick.

Adobe Acrobat has been around for decades. Most folks download the free reader and simply view PDF files. But that is just a reader. To edit the files I bought Acrobat Professional (I think it cost about $100). Suddenly I could actually test to see if all the fonts were included in the file. I could help set the initial view for a friend’s newsletter (it is a pain to try to read a newsletter that comes up with side-by-side pages since they are too small to read when they both show, so it is much more user friendly to view them as single pages stacked vertically). And finally I discovered the software includes Acrobat Distiller which enables the conversion of files and images to PDF. Lurking in Distiller is also a step that converts embedded RGB pictures into CMYK! The process is not particularly intuitive, but that 5-second process has made peace with the printer.

I suspect that Lightning Source has started demanding CMYK because of a fundamental difference between the two colour spaces. If you look back at the picture of the colour space you see the outlines of the spaces for RGB and CMY do not fully overlap. That means there are some colours you can see on your monitor that can’t be printed (and vice versa). I expect the fuss at Lightning Source is that customers saw a colour on their monitor and were disappointed when the book did not come back looking the same. So they want the publisher to do the conversion and take the heat!