Find index of unique pixel values and assign a color to the image. Original image is a grayscale.

I have a grayscale image in which objects are represented as:

Object Pixel Value

Background 0

Class 1 1

Class 2 2

Class 3 3

Class 4 4

Class 5 5

There are no other pixel values except the 6 mentioned above. Background is essentially present, other objects may or may not be present.

The requirement is to assign specific colors to the objects

Object Pixel Value Color

Background 0 Black

Class 1 1 Red

Class 2 2 Green

Class 3 3 Blue

Class 4 4 White

Class 5 5 Pink

For an example, i am attaching an image with Background, Class 4 and Class 5

Answer 1

[Walter Roberson]

cmap = [
    0 0 0    %black
    1 0 0    %red
    0 1 0    %green
    0 0 1    %blue
    1 1 1    %white
    1 0 1    %fuschia
    ];

filename = 'https://www.mathworks.com/matlabcentral/answers/uploaded_files/1081490/case_452_14.png';
grayimg = imread(filename);

imshow(grayimg, [])

rgbimg = ind2rgb(grayimg, cmap);

imshow(rgbimg)

[Rishi Raj]

Thanks a ton.. It works..

[Rishi Raj]

I am having trouble saving this png file, although it works perfectly with saving jpeg.

is there something unique about png?

Error message:

Error using writepng>CheckTextItem (line 378)

Text chunk must be a character vector or string scalar.

Error in writepng (line 258)

item = CheckTextItem(unmatched.(param_name));

Error in imwrite (line 566)

feval(fmt_s.write, data, map, filename, paramPairs{:});

Error in Grayscale2visiblegrayscale (line 23)

imwrite(rgbimg,path, 'Quality', 100);

%Convert GrayScale Values to Visible Image

srcFile=dir('/Users/rishiraj/Documents/MATLAB/Grayscale_Images/*.png');
disp(length(srcFile)); 
for i=1:length(srcFile)
    filename=strcat('/Users/rishiraj/Documents/MATLAB/Grayscale_Images/', srcFile(i).name);
    [pathstr,name,ext] = fileparts(filename);
    %disp(filename); 
    grayImage=imread(filename);
    cmap = [
    0 0 0    %black
    1 0 0    %red
    0 1 0    %green
    0 0 1    %blue
    1 1 1    %white
    1 0 1    %fuschia
    ];

    imshow(grayImage, [])    
    
    rgbimg = ind2rgb(grayImage, cmap);
    path=strcat('/Users/rishiraj/Documents/MATLAB/Grayscale_Images_Visible/',name, '.png');
    imwrite(rgbimg,path, 'Quality', 100);
end

[Rishi Raj]

ok.. png has to be saved with a different format.. the following code worked..

path=strcat('/Volumes/ESD-USB/_RISHI/TTV_png/Test/mask_visible/',name, '.png');
imwrite(grayImage,cmap, path);

[Walter Roberson]

The problem you had with writing the rgbimage is that 'Quality' is not a valid option for png files.