Image resolution.
Images viewed on a computer monitor or from the WWW should always be produced at 72 or 75 dpi (dots per inch - the screen resolution). Currently, most modern screen resolutions are 72 dpi. Some are 75 dpi and some are 96 dpi or higher. Screens with resolutions higher than 72 dpi will normally automatically compensate to display 72 dpi images. Displaying an image prepared for printing at 150 or 300 dpi will result in an image much larger that you intended. Dimensions of images for the WWW or multimedia should always be specified in pixels - not inches, cm, pica, em or other measurement - just pixels.

Colour
Before we examine the finer points of the different file formats, we should first examine the topic of image colour. Various aspects of an image's colour range may ultimately determine which format you choose and the final file size. Before you start you may wish to take a quick look at the glossary of some of the terms and nomenclature used in this tutorial, particularly those related to colour.

RGB is for SCREENS
When working with Web images, or any screen-based multimedia image, always use the RGB colour mode and model. All video display units, whether TV-style vacuum tube types or laptop LCD types all operate on additive, three colour principle and display variations of only Red, Green and Blue for each pixel.

CMYK vs. RGB
Masters of the print realm will instantly recognise the subtractive CMYK mode for printed images due to the base inks used in printing. However, RGB and CMYK are almost completely opposite to each other in the way they use colour in the image. For example, a CMYK image with the values C=0, M=0, Y=0, K=0 will be white, while an RGB image with the values R=0, G=0, B=0 will be black ! For multimedia and/or Web images, I believe that it is always best to ensure your image is in the RGB colour mode as early as possible in the preparation process to ensure that what you see as you prepare the image will be close to the final screen image.

Converting Image Formats
PhotoPaint converts images from one mode to another and makes a pretty good job of it with a range of choices. However, this is quite a big topic in itself and should be the thrust for another tutorial. Remember - if you have start with a CMYK or other non-RGB image, it is best to try and convert it early to avoid disappointment or difficulties after you have done a lot of work on the image.