灰度级数k，k=2^b，称该图像为b比特图像。
降低灰度级数是靠2的幂次方
网上代码：https://blog.csdn.net/silence2015/article/details/68927360
function changereduce_factor(imgpath,reduce_factor) % Write a computer program capable of reducing the number of intensity levels in an image from 256 to 2, % in integer powers of 2. The desired number of intensity levels needs to be a variable input to your program. f = imread(imgpath); if reduce_factor<0 reduce_factor=0 else if reduce_factor>8 reduce_factor=8 end end dfactor=uint8(2^reduce_factor); f_trans=(f/dfactor)*dfactor; subplot(1,2,1); imshow(f); subplot(1,2,2); imshow(f_trans); end
其中reduce_factor=8表示原图像是一张8bit图像，有灰度级dfactor是256，
所以（f/dfactor）取整只有两个结果0或者1，然后再乘灰度级就变成了黑白图片（只有两个灰度级）
那么当reduce不等于比特图像那个值的时候会出现什么结果，如果大于，那么图像是全黑的0，小于的话取整运算的结果将不只是0，1，还会出现更多数
但是还是小于比特图像数，也就做到了将灰度值降低。
pic=imread(\'pic/coltogray/1.jpg\'); ##gray_pic=rgb2gray(pic); ##figure(1) ##imshow(gray_pic) [x,y,z]=size(pic); graypic=zeros(x,y); level=4 dfactor=uint8(2^level) max1=0; min1=0; for i=1:x for j=1:y sum=0; for k =1:z sum=sum+pic(i,j,k)/3; end graypic(i,j)=sum; graypic1(i,j)=(sum/dfactor)*dfactor; end end graypic=uint8(graypic); graypic1=uint8(graypic1); figure(1); imshow(graypic); figure(2); imshow(graypic1); %将三维图像压缩至一维即可以看作是灰度图像？
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