Page 314 - Fundamentals of Light Microscopy and Electronic Imaging

IMAGE PROCESSING WITH FILTERS 297

Original
I

I Blurred

I Unsharp
masked

(a)

Original

Unsharp
masked

(b)
Figure 15-9
The strategy of unsharp masking for image enhancement. (a) Three intensity plots show a
boundary between two regions of different light intensity as depicted by the left-hand edge of
the light colored rectangles shown in drawing (b). The plots shown in (a) indicate: the original
image profile, a blurred version of the original, and an unsharp mask-corrected version
prepared by subtracting 50% of the blurred profile from the original profile. Notice that the
small negative and positive spikes in the unsharp mask plot are seen as bright and dark
edges in the bottom drawing. The amount of sharpening depends on the amount of blurring,
the amount of amplitude reduction created by subtraction of the blurred image, and the
amount of subsequent histogram stretching.