A digital image is composed of a finite number
of elements called pixels, each of which has a particular location and value
(intensity). Typically, pixels are organized in an ordered 2-dimentional array
(Matrix). The size of an image is
determined by the dimensions of this pixel array. The image width and height are the number of
columns and the number of rows in the array respectively. Thus, the pixel array is a matrix of M columns
x N rows. To refer to a specific pixel
within the image matrix, we define its coordinate at x and y positions.
Each pixel has
its own intensity value, or brightness.
If all the pixels have the same value, the image will be a uniform shade
i.e. all black, white, gray, or some other shade. It is in the type of intensity used for each
pixel that image types vary from one another.
Black and white images only have intensity of the black and white. Grayscale
images have intensity from the darkest gray (black) to lightest gray (white).
Color images, on the other hand, have intensity from the darkest and lightest
of three different colors, Red, Green, and Blue. The various mixtures of these color
intensities produce a color image.
values in digital images are defined by bits.
A bit is binary and only has two possible values, 0 or 1. An 8-bit intensity range has 256 possible
values, 0 to 255.
Two most basic
types of digital images are:
Digital Image Files
TIFF (also known as TIF), file types ending in .tif
for Tagged Image File Format. TIFF images create very large file sizes. TIFF
images are uncompressed and thus contain a lot of detailed image data. TIFFs
are also extremely flexible in terms of color and content.
JPEG (also known as JPG), file types ending in .jpg
for Joint Photographic Experts Group, which created this standard for this type
of image formatting. JPEG files are images that have been compressed to store a
lot of information in a small-size file. Most digital cameras store photos in
JPEG format, because then you can take more photos on one camera card than you
can with other formats.
GIF, file types ending in .gif
GIF stands for
Graphic Interchange Format. This format compresses images but, as different
from JPEG, the compression is lossless (no detail is lost in the compression,
but the file can’t be made as small as a JPEG).
PNG, file types ending in .png
PNG stands for
Portable Network Graphics. It was created as an open format to replace GIF,
because the patent for GIF was owned by one company and nobody else wanted to
pay licensing fees. It also allows for a full range of colour and better
Raw image files
files contain data from a digital camera (usually). The files are called raw
because they haven’t been processed and therefore can’t be edited or printed
yet. There are a lot of different raw formats–each camera company often has its
own proprietary format.