adjcontrast.m

来自「包内提供了Contourlet和Wavelet变换进行图像增强、去噪的各种算法和」· M 代码 · 共 34 行

% ADJCONTRAST - Adjusts image contrast using sigmoid function.
%
% function g = adjcontrast(im, gain, cutoff)
%
% Arguments:
%            im     - image to be processed.
%            gain   - controls the actual contrast; 
%                     A value of about 5 is neutral (little change).
%                     A value of 1 reduces contrast to about 20% of original
%                     A value of 10 increases contrast about 2.5x.
%                     a reasonable range of values to experiment with.
%            cutoff - represents the (normalised) grey value about which
%                     contrast is increased or decreased.  An initial
%                     value you might use is 0.5 (the midpoint of the
%                     greyscale) but different images may require
%                     different points of the greyscale to be enhanced.  


function newim = adjcontrast(im, gain, cutoff)

    if isa(im,'uint8');
	newim = double(im);
    else 
	newim = im;
    end
    	
    % rescale range 0-1
    newim = newim-min(min(newim));
    newim = newim./max(max(newim));

    newim =  1./(1 + exp(gain*(cutoff-newim)));  % Apply Sigmoid function