• Digital images are commonly obtained by the following methods.

• The first method is to digitize photographs and printed pictures using a scanner.

• In digital cameras, ADCs are built in. The second source of digital images is from individual frames of digitized video.

• In the third method, images are generated by some sort of graphics (painting) package.

Images can be:

Grayscale Image

• An image displayed on a computer monitor consists of many small dots. Theses dots are called pixels. There are a fixed number of pixels on a horizontal line and a fixed number lines in the vertical dimension (i e, a digital image consists of a rectangular array of pixels).

• Different pixels may have different brightness or intensity. The intensity range from black to white depends on the required image quality or number of bits used for each pixel. For example, when 8 bits are used to represent a pixel, a total of 256 different intensity levels can be represented, black being 0 and white being 255.

• The arrangement of these pixel values in a contiguous region of in memory in array form is called a bitmap.

• Example

Color Image

• A color image also consists of a rectangular array of pixels. The only difference from gray scale images is that we need three values to represent each pixel.

• Each value represents one primary color. This representation is based on the tri stimulus theory of color production, which states that any color can be reproduced by an appropriate mixing of three primary colors. The primary colors used in television systems and computer monitors are red, green, and blue.

• Therefore a color image can be represented by three two-dimensional arrays, corresponding to the red, green and blue components of the image, respectively.

• Example:

Monochrome Image

• Monochrome photos are photos that contain variations of only one color and nothing else. This could be different shades of blue, green, or grey, for example.

• In computing, monochrome has two meanings:

• it may mean having only one color which is either on or off (also known as a binary image),

• allowing shades of that color.

• Each pixel is stored as a single bit.

• Example