Computer Graphics (Assignment)

By: Farwa Abdul Hannan (12 – CS – 13)

Raster Images: Raster images are those images that are made up of many small cells. These cells are known

as Pixels. A raster is stored in a computer as an array of numerical values. Each numerical value

represent the value of the pixel stored there. This array as a whole often known as Pixel Map.

Raster images are of two forms

1. Gray Scale Raster Images

2. Colored Raster Images

Gray Scale Raster Images:

These images as cleared from the name are in different shades of gray. The gray levels

range from black to white. As we know that raster images are stored in numerical values so if in

gray scale raster images, there are only two values of pixel then we call this image a bi-level image

as its pixel map can be consisted of an array of 1s or 0s or any two values from the one stored

between them (1s for black and 0s for white and the values between them represent different shades

of gray). A bi-level image is often known as 1 bit per pixel image. In a gray scale image if the

pixels take on more than two values then each pixel requires more than a single bit in memory and

their values are:

1. 2 bits/pixel produce 4 gray levels

2. 4 bits/pixel produce 16 gray levels

3. 8 bits/pixel produce 256 gray levels

Color Raster Images:

As the colored images represents our daily experience more closely as compared to gray

scale images so these images are more desirable. Color raster Images are most commonly used

images. Ina color raster image each pixel has a color value represented by a numerical value against

each color. In these images the colors are described as a combination of amounts of red, green and

blue colors. Each pixel value consist of 3-tuple like (red, green and blue) and these tuples

represents the intensities of red, green and blue colors respectively. The number of bits are used to

represent each pixel. Each value in the 3-tuple (red, green and blue) has a certain bit for it. For

example in the pixel values (0, 1, 1) 0 means off and 1 means on so here against the 3-tuple (red,

green, blue) red is off as it is 0 and green and blue are on as their pixel value in 1. Possible

combinations of colors with different pixel values are:

The colors other than these are produced by using different intensities of these colors.