Wide Format Imaging

One of the problems in this industry is that a lot of terms have overlapping meanings. They overlap even when referring to the same files or the same processes. And therein certainly lies some of the confusion when talking about the whole issue of working with RGB or CMYK files. Fact is, that as used in the context of describing the makeup of a file, the terms RGB and CMYK only refer to the numerical definitions of each pixel in an image. Your screen--for instance--creates colors out of red, green, and blue. If you convert an RGB file to CMYK while you're viewing it, you didn't just make your screen into a CMYK device, you just altered that file's pixel information from—basically—three numbers per pixel (red value; green value; blue value) to four numbers per pixel (cyan value; magenta value; yellow value; black value.)

That's it. The first thing I tell clients when I do a color space demonstration is that computers are stupid. Fighting color issues constantly again and again and again and again, it's easy to get the idea that computers are devilish and gremlin-filled and they cackle in sheer delight as they turn grey to green and purple to brown at the most inopportune of times, but that really isn't true. What's true is that computers don't know the first thing about color. They only know numbers, and each and every time you tell them to do something, they'll do exactly what you say. If you pick a workflow color space, tag all your files and conform all your applications to that space, then you'll get consistent color each and every time. If you don't, if you leave all your applications to their own default devices, then each time you take a file through an application with a differing default color space, you'll alter the color information of the pixels in your file.

More often than not, that right there is the cause of folks issues with color and color management. However, what happens is that they then go off chasing entire flocks of wild geese to alter this profile and download that profile and try this or that at the printer or in the RIP, and that isn't even where the problem is.

So how does it work? Pretty simply, actually. Every digital image is, of course, in the end just a bunch of little boxes with numbers in them. Pixels. The numbers—also of course—relate to color. In 8-bit RGB, each pixel contains a number 0-255 for red value, a number 0-255 for green value, and a number 0-255 for red value. And again, that's it. That's the end of the story and nothing more.

The key is, 0-255 as relates to...what?

If one RGB space is bigger than another RGB space, then, for instance, it might be able to get a much greener green than the other space. Problem is, in both spaces, green as green can be is going to be defined as 0 (no red) -255 (green as green can be) -0 (no blue.) Unless you tag all your files with the space in which you worked them in one application, and unless all your applications are set up to honor the tag and work in that color space as well, what they'll do as you move your file between them is assume the pixels in your file are defined as whatever color space is their default. And change your file for you accordingly.

Helpful.

Okay, so, all the more reason to work in CMYK then, right?

Wrong.

CMYK is device dependent too. In a CMYK file, there are four numbers per pixel, related to you by all the applications for easy understanding as cyan, magenta, yellow and black values, 0-100 percent. That's why, incidentally, CMYK files are bigger then RGB files. They've got one more piece of data per pixel. But again, those values have to relate to something. And what they relate to in each case is a certain color of ink printed at a certain density. In the case of the Adobe applications' default CMYK space of SWOP, the colors are litho process cyan, magenta, yellow and black printed on coated stock at SWOP densities.

And the fact is, SWOP is a relatively tiny gamut compared to most wide-format imaging devices. But more to this point, it again is just one device-dependent color space. Not all applications use it as a CMYK default; so once again, as you move from application to application, if you don't tag all your files and set all your color space information in all your applications the same, each application will assume your file's pixels color values were created using its own default color space, and helpfully alter them for you accordingly.