Mode of Image (An Important Property)

Combination of all three of red, green, and blue in equal intensities makes white.

The most basic property of an image is its mode. There are three possible modes: RGB, grayscale and indexed.

  

RGB stands for Red-Green-Blue, and indicates that each point in the image is represented by a "red" level, a "green" level, and a "blue" level. These color levels are represented by color channels and thus at each point in the image there are channels: red channel, green channel, blue channel and alpha channel, representing opacity. Each color channel has 256 possible intensity levels.

In a grayscale image, each point is represented by 2 channels: (1) Brightness channel and (2) Alpha channel. Brightness channel defines a brightness value, ranging from 0 (black) to 255 (white), with intermediate values representing different levels of gray.

 

Grayscale Image

Now as we know that alpha channel represents opacity, so when the alpha value of alpha channel at a given location in a given layer is zero, the layer is completely transparent and when alpha is maximal, the layer is opaque. Intermediate alpha values correspond to varying degrees of translucency.

 

In an Indexed image, only a limited set of discrete colors are used, usually 256 or less. These colors from the "color-map" of the image, and each point in the image is assigned a color from the color-map. Thus, indexed image adopts different methodology to represent colors compared to the channel system adopted in RGB and grayscale images.

4-color indexed image

16-color indexed image

256-color indexed image