Page 241 - Digital Analysis of Remotely Sensed Imagery

Image Enhancement 205

Frequency 1 23 4 5 6 7

DN
(a) (b)

(c)
FIGURE 6.1 Effect of density slicing. The raw image (a) in grayscale is color-coded
(c) after the pixel values are discretized into seven levels using the thresholds
(b) shown in the histogram.

6.1.2 Linear Enhancement
In linear enhancement the output value of a pixel is modified from
its input value via a linear function (Fig. 6.2). The slope of the linear
function dictates the degree of stretching. Its tangent of the angle
with the horizontal axis (q ) represents the coefficient through which
contrast is altered. If tan q > 1, then the enhanced image has a larger