Convert an RGB image to grayscale but keep one color?

A = imread('C:\FFOutput\gdgf\B.jpg'); B = rgb2gray(A); figure(1),imshow(B);

I have converted the image to a grayscale but don't know how to keep one color especially green.

Answer 1

[yonatan gerufi]

Hi, there are several ways to do it,

i find it easy to do:

red_color = A(:,:,1);
green_color = A(:,:,2);
blue_color = A(:,:,3);

[Jaja]

how can I add this to my code to keep the green one? can you give me an example with the code??

Answer 2

[John]

I am guessing you want the green channel stored in a separate matrix. In your code, A is only read. Its value does not change after the call to rgb2gray. To get the green channel from A:

greenChannel = A(:,:,2);

[Jaja]

nothing happens actually. can you give me an example with the code??

Answer 3

[Image Analyst]

I just answered this an hour ago for someone. See my comment http://www.mathworks.com/matlabcentral/answers/153732-question-concerning-color-segmentation-performance#comment_235875

[Image Analyst]

Code is attached.

[Jaja]

I actually want to keep the color green in the picture and the rest of the color is in the grayscale

[Image Analyst]

Why? That's pretty much what the original image is already.

Answer 4

[DGM]

Refer to this answer for more details on how this can be done. While that link includes multiple methods, I'm going to use MIMT replacepixels() for ease of use.

% this is a color image
rgbpict = imread('coloredChips.png');

% create a grayscale copy by some means
graypict = rgb2gray(rgbpict); % BT601 luma

% HSV ranges for masking
rangeR = [0.963 0.016; 0.258 1; 0.338 1];
rangeG = [0.380 0.453; 0.258 1; 0.338 1];

% create masks to select objects of specified colors
hsvpict = rgb2hsv(rgbpict);
maskR = all(hsvpict >= permute(rangeR(:,1),[2 3 1]),3) ...
    | all(hsvpict <= permute(rangeR(:,2),[2 3 1]),3);
maskG = all(hsvpict >= permute(rangeG(:,1),[2 3 1]),3) ...
    & all(hsvpict <= permute(rangeG(:,2),[2 3 1]),3);

% clean the masks
maskR = bwareaopen(maskR,100);
maskG = bwareaopen(maskG,100);

% composite the color and gray images using the masks
% replacepixels is from MIMT
outpictR = replacepixels(rgbpict,graypict,maskR);
outpictG = replacepixels(rgbpict,graypict,maskG);

See this answer for more details on how the masking could be done for this particular image.

See also this thread about different ways of partially desaturating a part of an image.