The resolution of a digital image depends on two parameters
(i) No.of samples of the digital image (N)
(ii) No. of grey levels (m)
The more these parameters are increased,the closer the digitized array approximates the original image. However, the amount of memory space and the processing requirements increase drastically as function of these two factors.
A good image is difficult to define, because image quality not only is highly subjective, but is also strongly dependent on the requirements of a given application. The quality of an image is greatly varied by variation in the above mentioned factors.Thus the two methods of varying the quality of the images are:
Spatial Resolution:- Here the number of samples of digital image is changed as a power of two keeping the display area used for each image the same, and maintaining a constant gray level. The pixel in the lower resolution images are duplicated in order to fill the entire display .This pixel replication produced a checkerboard effect, which is particularly visible in images of lower resolution.
Tonal Resolution:- In Tonal Resolution, the quality of images is varied by decreasing the number of bits used to represent the no. of gray levels in an image.The effects on image quality produced by varying N and m are subjectively analyzed by the level of detail pertaining to an image.
The general conclusion that can be drawn from such a subjective study are:
(i) In most cases the quality of the image tends to increase as N and m are increased .In few cases, for affixed N ,the quality improved by decreasing M the reason being that a decreased in M generally increases the apparent contrast of an image.
(ii) For images with a large amount of detail only a few gray levels are needed. Increased gray levels for an image of a mob. For e.g. may increase their obscurity of the image.