Question

我编写了有色图像直方图均衡的代码。该代码适用于灰度图像，但它会导致彩色图像出错。我正在将rgb图像转换为hsv然后执行直方图均衡。有什么想法吗？

代码：

%  GIm=imread('tire.tif'); this is grayscale image, which works fine
I=imread('D:\came.jpg');
GIm=rgb2hsv(I);% converting color image to hsv
numofpixels=size(GIm,1)*size(GIm,2);
figure,imshow(GIm);
title('Original Image');
HIm=uint8(zeros(size(GIm,1),size(GIm,2)));
freq=zeros(256,1);
probf=zeros(256,1);
probc=zeros(256,1);
cum=zeros(256,1);
output=zeros(256,1);
%freq counts the occurrence of each pixel value.
%The probability of each occurrence is calculated by probf.
for i=1:size(GIm,1)
    for j=1:size(GIm,2)
        value=GIm(i,j);
        freq(value+1)=freq(value+1)+1; % giving error here 
        probf(value+1)=freq(value+1)/numofpixels;
    end

end

sum=0;
no_bins=255;
%The cumulative distribution probability is calculated. 
for i=1:size(probf)
   sum=sum+freq(i);
   cum(i)=sum;
   probc(i)=cum(i)/numofpixels;
   output(i)=round(probc(i)*no_bins);
end

for i=1:size(GIm,1)
    for j=1:size(GIm,2)
            HIm(i,j)=output(GIm(i,j)+1);
    end
end

figure,imshow(HIm);
title('Histogram equalization');
subplot(2,2,2); 
plot(GIm);
%bar(GIm);
title('Before Histogram equalization');
subplot(2,2,4);
plot(HIm)
%bar(HIm);
title('After Histogram equalization');

错误：

Attempted to access freq(1.61378); index must be a positive integer or logical.

Error in histogramequ (line 18)
        freq(value+1)=freq(value+1)+1;

Answer 1

你的代码的主要问题是在rgb2hsv（）之后，每个像素的格式在[0,1]中是双倍的，而不是uint8。所以你需要转换回[0,255]所以它可以用作下标。

以下代码可以正常使用。

for i=1:size(GIm,1)
    for j=1:size(GIm,2)
        value=floor(GIm(i,j) * 255);  % now value is in [0,255]
        freq(value+1)=freq(value+1)+1;
        probf(value+1)=freq(value+1)/numofpixels;
    end
end

Matlab：索引必须是正整数或逻辑

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