如何将RGB图像转换为灰度但保持一种颜色？ [英] How can I convert an RGB image to grayscale but keep one color?

问题描述

所以我试图创建一个类似于罪恶城市或其他电影的效果，他们从图像中除去一个颜色。

So I am trying to create an effect similar to Sin City or other movies where they remove all colors except one from an image.

我有一个RGB图像我想转换为灰度，但我想保持一种颜色。

I have an RGB image which I want to convert to grayscale but I want to keep one color.

这是我的照片：

img src =https://i.stack.imgur.com/EcyOd.jpgalt =alt text>

我想保持红色。其余的应该是灰度。

I want to keep the red color. The rest should be grayscale.

这是我的代码输出到目前为止（你可以看到，区域是正确的，我不知道为什么他们是白色，而不是红色）：

This is what my code outputs so far (you can see that the areas are correct, I don't know why they are white instead of red though):

这里是我的代码到目前为止：

Here is my code so far:

filename = 'roses.jpg';

[cdata,map] = imread( filename );
% convert to RGB if it is indexed image
if ~isempty( map ) 
   cdata = idx2rgb( cdata, map ); 
end

%imtool('roses.jpg');

imWidth = 685;
imHeight = 428;

% RGB ranges of a color we want to keep
redRange = [140 255];
greenRange = [0 40];
blueRange = [0 40];

% RGB values we don't want to convert to grayscale
redToKeep = zeros(imHeight, imWidth);
greenToKeep = zeros(imHeight, imWidth);
blueToKeep = zeros(imHeight, imWidth);

for x=1:imWidth

    for y=1:imHeight

        red = cdata( y, x, 1 );
        green = cdata( y, x, 2 );
        blue = cdata( y, x, 3 );

        if (red >= redRange(1) && red <= redRange(2) && green >= greenRange(1) && green <= greenRange(2) && blue >= blueRange(1) && blue <= blueRange(2))
            redToKeep( y, x ) = red;
            greenToKeep( y, x ) = green;
            blueToKeep( y, x ) = blue;
        else
            redToKeep( y, x ) = 999;
            greenToKeep( y, x ) = 999;
            blueToKeep( y, x ) = 999;
        end

    end 

end 

im = rgb2gray(cdata);
[X, map] = gray2ind(im);
im = ind2rgb(X, map);

for x=1:imWidth

    for y=1:imHeight

        if (redToKeep( y, x ) < 999)
            im( y, x, 1 ) = 240;
        end
        if (greenToKeep( y, x ) < 999)
            im( y, x, 2 ) = greenToKeep( y, x );
        end
        if (blueToKeep( y, x ) < 999)
            im( y, x, 3 ) = blueToKeep( y, x );
        end

    end 

end 

imshow(im);

推荐答案

figure
pic = imread('EcyOd.jpg');

for mm = 1:size(pic,1)
    for nn = 1:size(pic,2)
        if pic(mm,nn,1) < 80 || pic(mm,nn,2) > 80 || pic(mm,nn,3) > 100
            gsc = 0.3*pic(mm,nn,1) + 0.59*pic(mm,nn,2) + 0.11*pic(mm,nn,3);
            pic(mm,nn,:) = [gsc gsc gsc];
        end
    end
end
imshow(pic)

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