A digital image is a numeric (binary) representation of
a two dimensional image.
Digital images are of two types
• Raster Image
• Vector Image
Digital image usually refer to raster or bitmapped
A Raster graphics image is a dot matrix data structure
representing a rectangular grid of pixels or points of
The smiley face in the bottom left corner is a
bitmap image. When enlarged, individual pixels
appear as squares. Zooming in further, they can
be analyzed, with their colors constructed by
adding the values for red, green and blue.
In raster image pixel is the smallest addressable
element which have its own characteristic.
In a digital image each pixel has its own color value
generally in rgb format.
Colour depth (bit depth) is the number of bits used to indicate colour of a
single pixel in a digital image.
COLOUR DEPTH NUMBER OF
16777216 or 16M
Color Depth:1 bit
Color Depth:2 bit
Color Depth:8 bit
Color Depth:4 bit Size:
Color Depth:24 bit
RASTER IMAGE SIZE
The bits representing the bitmap pixels may be packed or
unpacked (spaced out to byte or word boundaries),
depending on the format or device requirements.
Depending on the color depth, a pixel in the picture will
occupy at least n/8 bytes, where n is the bit depth.
Size of image (in Bytes)=width*height*n/8
Vector graphics is the use of geometrical primitives such as
points, lines, curves, and shapes or polygon(s), which are all
based on mathematical expressions, to represent images in
Any particular vector file format supports only some kinds of
primitive objects. Nearly all vector file formats support simple and
fast-rendering primitive objects:
Lines, polylines and polygons
Bézier curves and bezigons
Circles and ellipses
Vector art is ideal for printing. Since the art is made from a series
of mathematical curves, it will print very crisply even when
resized. For instance, one can print a vector logo on a small
sheet of copy paper, and then enlarge the same vector logo to
billboard size and keep the same crisp quality.
The World Wide Web Consortium (W3C) standard for vector
graphics is Scalable Vector Graphics (SVG). The standard is
complex and has been relatively slow to be established at least
in part owing to commercial interests. Many web browsers now
have some support for rendering SVG data.
Vector images could be magnified to any amount, it never
breaks into small pixels.