Hey, you say. You're printing in 4-color process. Wouldn't you prefer CMYK?
Well, no. Not exactly. Here's why.
CMYK is not, properly speaking, a color space. It is a separation specification. That is, the CMYK are INK colors. The CMYK file is made up of four separate grayscale images.
Although great effort is made to ensure uniformity across different media, it is an inescapable fact, (you just can't get away from it), that different machines, papers, and inks or toners all print differently. The difference between what you tell a machine or process to print and what you actually get can be graphed on a grid. The result is called a Tonal Response Curve, or TRC.
Ideally, the curve should be linear--a straight line from zero to 100 percent at a 45 degree angle. It never is. Every device's TRC is different, as is every ink's and every toner's. And paper. In order to deliver an image the way it's "supposed" to look, the color separations need to be made to suit the TRC of the machine, inks, and papers being used. Some of these decisions need to be made "on the fly", according to scheduling demands and other specs over which you have no control. The wisest course is to send us RGB bitmap files and let us to the conversion.
If you already have a CMYK file, do not convert it back to RGB. We can make a profile-to-profile conversion. Though this is not the best course, in most cases it will suffice.
The best format to use is TIFF. Use LZW compression in Photoshop.
The best RGB color space we have found is the one created by MacWorld columnist and Real World Photoshop author Bruce Fraser. This is generally called FraserRGB or BruceRGB. The ICC profile has spread quite widely and is probably on your program disks. If at all possible, you should avoid sRGB.
Also...
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