Bad lighting condition or lighing calibration often results in
images with bad contrast. There exist many techniques that
try to correct the image contrast (constrast enhancing). The
algorithm used in the Bit program is the histogram
equalizationenhance1 method, which adjusts
the pixel intensity levels so that the resulting image is uniform,
thus maximizing the zeroth-order entropy of the image. It is
also easy to implement. All it takes is the following transformation
where F is the mapping function that transforms the
input pixel intensity I to the output pixel intensity J;
N is the total number of pixels and nk is the
number of pixels having the intensity k.
The original algorithm is proposed for grayscale images
and it is extended to the color images in the Bit program. Instead
of performing the transformation defined by to
equalize the RGB histogram seperately, the Bit program uses
a comman transforming function and applies it to the RGB colors.
The common tranformation is the one defined by gray intensity
of the image. This transformatin has the virtue of keeping
the overall RGB ratio the image. In almost all cases tested,
the enhanced image is somewhat better and also a little brighter.