Color management is inherently different on Mac and PC. It is also different if you want to correct for web or for printing on an Epson printer for example, or at a print plant in CMYK. On the two machines: you MUST calibrate the monitor, using ColorSync on Mac and Adobe Gamma on PC. Set the temp color of the monitor to 6500K. It's the same as the sun, so when you'll modify photos on the screen, you'll be with a correct setting. On the PC: for web, the color space is, now, sRGB in 24 Bit systems, and the 216 Web Colors in 8 Bit systems. On the macintosh: the same apply. Of course, if the monitor of, say, somebody browsing the web is not calibrated, the colors will be bad and you can't do anything to that. In printing on a Epson or similar printer, you must understand that the printer is RGB, as the screen. You must chose the correct settings corresponding to the paper you use and then the driver will do the correct CMYK (or else) separation to send to the printer. But you must keep in mind that the Epson system is RGB. If you'll print at a print plant, first call them and ask for details about CMYK separation. They will flash your files and know these settings. You'll then set them in Photoshop preferences. Feel free to email me.

A little bit more: the resolution of an image and the printing resolution of, say, an Epson printer are two different things. For the Epson, in fact, we'll speak of "diffusion" of ink droplets. So you don't need to have an image at 1400 dpi to print at 1400 dpi on an Epson. Just use a 300 dpi image, and print at the 720 diffusion, which is usually excellent... Otherwise the file size will be incredible...

For an image for web, or only for looking on a screen, the resolution is 72 dpi. When you scan an image, the higher the resolution, the more details you'll have. The filters you'll apply will have better results. It's common use to scan at, say, 600 dpi, work on the image, then go down to 300 dpi for printing. That resolution has been choosen because it's roughly 12 line per mm, which is the eye resolution. But there are cases where the output media is resolution fixed, as a screen, where it is 72 dpi. When you use an photo from a library, say a 30*45 cm @ 150 dpi, if you need the size of the photo to be smaller, don't resample and so the resulting resolution will be higher. You are keeping the details which are there. Last,if you have an image at 72 dpi, on push the resolution to, say, 150 dpi, the quality will stay the same. The file will only be bigger. You can't invent details...

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