This question is very important. Before to give any other commissions to our artwork designer, I need to know crucial information about prepress. These artworks should be later printed into intruction booklets, magazines etc. What do we need to know about prepress? Color Management? Resolution? Difference between CMYK and RGB? Can we change a drawing that was already done into RGB easily into CMYK? Do you know about CMYK colour space? the difference between PPI and DPI? How should we work in CMYK? Would it work to do it in RGB then convert? Thank you! You could spare us a lot of time with your replies! Elder Prince www.blossomsoft.com

I've got a little prepress experience.

From the looks of things, the press people should be able to answer most of your questions. You should call up a printer and ask him questions. For better results seek out a computer savvy printer.

Resolution. They tend to use lines per inch rather than dots per inch. Iirc the ratio is 2:1 - so that 65 lpi -> 130 dpi.

CMYK - The final product will most definitely need to be cmyk. It's probably a good thing to convert your press graphics from rgb to cmyk. Yes, it's easy to change from rgb to cmyk - the color spaces are the opposite of each other.

C = 1 - R;
M = 1 - G;
y = 1 - B;
K = min3(C, M, Y);
C -= K;
M -= K;
Y -= K;

The DPI/ LPI/ PPI doesn't really matter, that stuff should be handled by the printshop's preprocessor. Because, the resolution depends completely on the printer. If you print a 640x480 image at maximum resolution on an offset printer (277000 DPI), the image would be much smaller than a stamp... ;-)

There's only one thing to keep in mind regarding the resolution: the higher, the better. That is, if you want to print an image at A4 (210x297mm) in good quality, the image should be 2000x3000 pixel.

The color space is a different issue. The main problem is, 32bit CMYK has more colors than RGB (8bit C, M, Y, K = 32bit <-> 8bit R, G, B = 24bit - alpha doesn't count). So, you'll get the best possible output if you create all images at HDR color depth (10bit, 12bit, 16bit int or 32bit float per channel RGB), at a resolution of 2000x3000 px+...