Unsharp masking and crispening
The unsharp masking technique is commonly used in the printing industry for crispening of edges. A signal proportional to the unsharp or low pass filtered version of the image is subtracted from the image. This is equivalent to adding the gradient or a high pass signal, to the image. In general the unsharp masking operation can be represented by.
 where  and  is a suitably defined gradient at ( m,n ).
Commonly used gradient function is the discrete Laplace gradient
Figure (5.14):Unsharp masking operations
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Magnification and Interpolation (Zooming)
(Zooming by replication)
Replication is a zero order hold where each pixel along a scan line is repeated and then each scan line is repeated. Replication is a ZOH where each pixel along a scan line is repeated and then each scan line is repeated. This is equivalent to taking an M ´ N image and interlace it by rows and columns oif zeros to obtain a 2 M ´ 2 N matrix and convolving the result with an array H defined as
This gives 
for 
eg.  —› zero interlace  convolve H  |
