数字图像处理：图像的灰度变换（Matlab实现）

(1)线性变换:

通过建⽴灰度映射来调整源图像的灰度。

k>1增强图像的对⽐度；k=1调节图像亮度，通过改变d值达到调节亮度⽬的；0i = imread('theatre.jpg');i = im2double(rgb2gray(i));[m,n]=size(i);%增加对⽐度Fa = 1.25; Fb = 0;O = Fa.*i + Fb/255;

figure(1), subplot(221), imshow(O);

title('Fa = 1.25, Fb = 0, contrast increasing');figure(2),subplot(221), [H,x]=imhist(O, 64);stem(x, (H/m/n), '.');

title('Fa = 1.25, Fb = 0, contrast increasing');%减⼩对⽐度Fa =0.5; Fb = 0;O = Fa.*i + Fb/255;

figure(1), subplot(222),imshow(O);

title('Fa = 0.5, Fb = 0, contrast decreasing');figure(2), subplot(222), [H,x] = imhist(O, 64);stem(x, (H/m/n), '.');

title('Fa = 0.5, Fb = 0, contrast decreasing');%线性亮度增加Fa = 0.5; Fb = 50;O = Fa.*i + Fb/255;

figure(1), subplot(223), imshow(O);

title('Fa = 0.5, Fb = 50, brightness control');figure(2), subplot(223), [H,x]=imhist(O,64);stem(x, (H/m/n), '.');

title('Fa = 0.5, Fb = 50, brightness control');%反相显⽰

Fa = -1; Fb = 255;O = Fa.*i + Fb/255;

figure(1), subplot(224), imshow(O);

title('Fa = -1, Fb = 255, reversal processing');figure(2), subplot(224),[H,x]=imhist(O, 64);stem(x, (H/m/n), '.');

title('Fa = -1, Fb = 255, reversal processing');(2)对数变换：

增强低灰度，减弱⾼灰度值。i = imread('theatre.jpg');

i = rgb2gray(i);i = double(i);

out1 = log(1+i)/0.065;out2 = log(1+i)/0.035;

out1(find(out1>255)) = 255;out2(find(out2>255)) = 255;out1 = uint8(out1);out2 = uint8(out2);

(3)幂次变换：

次数⼩于1时，增强低灰度，减弱⾼灰度；次数⼤于1时增强⾼灰度，减弱低灰度。i = rgb2gray(imread('theatre.jpg'));i = double(i);

y1 = 255*(i/255).^2.5;y2 = 255*(i/255).^0.4;

y1 = uint8(y1);y2 = uint8(y2);

(4) 指数变换：

增强⾼灰度，减弱低灰度。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：

有时图像灰度集中在某⼩块区域，需要改变图像对⽐度。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);%均衡函数(7)直⽅图规定化：实现局部的灰度均衡。

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

img_ref = rgb2gray(imread('rpic.jpg'));%参考图，按照这个的的直⽅图进⾏规定化[hgram, x] = imhist(img_ref);J = histeq(img, hgram);