At least 800 pixels or more can meet the requirements of printing.

When the picture size is in pixels, you need to specify a fixed resolution in order to convert the picture size to the actual size in reality. For example, the resolution of most commonly used pictures for most webpages is 72, that is, pixels per inch is 72, and 1 inch is equal to 2.54 centimeters. Then by conversion, you can get 28 pixels per cent.

The number of different colors a pixel can express depends on the bit-per-pixel (BPP). This maximum number can be obtained by taking the power of the color depth of two.