(4) 指數(shù)變換：

增強高灰度，減弱低灰度。

i = imread('theatre.jpg');

i = rgb2gray(i);

i = double(i);

y1 = 1.5.^(i*0.070)-1;

y2 = 1.5.^(i*0.050)-1;

y1(find(y1>255)) = 255;

y2(find(y2>255)) = 255;

y1 = uint8(y1);

y2 = uint8(y2);

(5)灰度拉伸：

有時圖像灰度集中在某小塊區(qū)域，需要改變圖像對比度。

i = imread('theatre.jpg');

i = rgb2gray(i);

L = imadjust(i,[ ],[50/255;150/255]);

J = imadjust(L,[50/255;150/255 ],[20/255;230/255]);

(6)灰度均衡：

i = rgb2gray(imread('theatre.jpg'));

LC = imadjust(i,[ ],[50/255;150/255]);

HE1 = histeq(LC);%均衡函數(shù)

(7)直方圖規(guī)定化：

實現(xiàn)局部的灰度均衡。

img = rgb2gray(imread('theatre.jpg'));

img_ref = rgb2gray(imread('rpic.jpg'));%參考圖，按照這個的的直方圖進行規(guī)定化

[hgram, x] = imhist(img_ref);

J = histeq(img, hgram);