General note

General notes

Monochrome images also referred to as black-and-white or bitonal use one bit to represent each pixel color (black or white). Greyscale images, also referred to as grey-level, consist of different grey tone pixels. Grey levels vary from 0 (black) to 255 (white). Thus, one byte is sufficient to store information on each pixel color in greyscale images.

Depending on the color information number of bits a color image can require 4, 8, 16, 24 or 32 bits per pixel to represent a color. Colors can be made by mixing of three basic colour components in different proportions. These components are known as the primary colors: red, green and blue (RGB model). Each component has 256 levels (from 0 to 255). The RGB color image is an image that requires three bytes (24 bits per pixel) to store color information of each pixel; one byte (256 brightnesses) is required for each of the primary colours.
The HSV model is based on color perception by the human eye. In the HSV model all colors are described in terms of three basic characteristics:
• Hue is the wavelength of light reflected from or transmitted through an object. More commonly, hue is identified by the name of the color, such as red, orange, or green. Hue is measured as a location on the standard color wheel and expressed as a specific angle between 0° and 360°.
• Saturation is an analogue of the intensity or purity of a color. Saturation represents the amount of grey in relation to the hue and is measured as a percentage from 0 percent (grey) to 100 percent (fully saturated).
• Value (or brightness) is the relative lightness or darkness of the color and is usually measured as a percentage from 0 percent (black) to 100 percent (white).
Note that scaling an image implies the distortion of colour since the colours of dots on the image can be mixed in one pixel (scale less then 1:1) or, in the opposite case, several pixels on the screen represent one dot (scale greater then 1:1). Hence for the most precise color match on the screen, set the scale to 1:1 (one dot on the image corresponds to 1 pixel on the screen).