When images are converted from one form to another they are subject to
nonlinear transformations that reduce the output quality. This paper
presents an image enhancement technique based on fuzzy relations that
can be applied to improve the appearance of these images. A grey-scale
image I with M rows and N columns is viewed as a weighted relation fr
om a set X with M elements into a set Y with N elements with g(x, y) r
epresenting the grey-value at location (x,y) in I. An appropriate choi
ce of two thresholds corresponding to pixels close to black and white
pixels is made which partitions the image into crisp and fuzzy pixels.
The fuzzy pixels correspond to pixels which are either black or white
with a certain degree of membership between 0 and 1. The original ima
ge is transformed into an enhanced image by forming its dual complemen
t. This is achieved by first constructing fuzzy sets a, and a, on X an
d Y respectively and applying these fuzzy sets to manipulate only the
fuzzy pixels in I. After the entire transformation, the maximally fuzz
y pixels, that is, pixels with membership value equal to 1/2, get enha
nced towards either black or white, depending on the neighborhood pixe
ls of the segment to which they belong. The performance of the propose
d technique is demonstrated on several images. Enhanced images obtaine
d using other techniques are also presented for comparison.