MATLAB: Gray image to rgb using ind2rgb

gray image to rgb using colormapImage Processing Toolbox

please can someone show me how to convert a rgb image to gray and convert that gray image back to rgb using ind2rgb…. how to obtain map for the function ind2rgb….. Please do reply….

Best Answer

You cannot convert grayscale images back to rgb without loss of information. Many different combinations of RGB values convert to the same grayscale level, so if all you have at a location is the grayscale level, then you cannot know which of the 65536 RGB values that map to the exact same grayscale that the RGB came from.

You can convert RGB to pseudocolor (ind). You could save a copy of the map used for that. You could convert each member of the pseudocolor map into grayscale and display it that way, and later you could convert back the pseudocolor map into RGB. However, if you want to do anything that modifies the grayscale (such as adaptive equalization) then you will have trouble.

[indimg, indmap] = rgb2ind(YourImage);
indasgray = rgb2gray(reshape(indmap,[size(indmap,1),1,3]));
image(indimg);
colromap(indasgray);   %image painted gray but multiple ind might have same gray
ReconstructedImage = ind2rgb(indimg, indmap);   %not indasgray

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MATLAB: How to get a dithered color image

I've never used dither() so I don't know what it does. But to answer your questions:

(1) Yes. It's called ind2rgb().

rgbImage = ind2rgb(indexedImage, customColorMap);

(2) Call rgb2ind():

[indexedImage, customColorMap] = rgb2ind(grayImage, numColors);

MATLAB: Convert grayscale to RGB

Try it like this if you want to pick some color out of the jet colormap:

workspace;  % Make sure the workspace panel is showing.
format longg;
format compact;
fontSize = 20;
% Create a jet colormap
c = 128;
map = jet(c);
pO2value=double(109); % 109 is an arbitrary number out of 1:128
r = ceil(map(pO2value,1)*c)
g = ceil(map(pO2value,2)*c)
b = ceil(map(pO2value,3)*c)
% Now let's do it to a gray scale image.
% Read in a standard MATLAB gray scale demo image.
grayImage = imread('cameraman.tif');
handleToFigure2 = figure;
subplot(2,2,1);
imshow(grayImage);
title('Gray Image', 'FontSize', fontSize);
% Enlarge figure to full screen.
set(gcf, 'units','normalized','outerposition',[0 0 1 1]);
% Convert the gray image into RGB so we can get it into hsv space.
rgbImage = cat(3, grayImage, grayImage, grayImage);
hsv = rgb2hsv(rgbImage);
% Make the hue plane of the hsv image this same hue
hsvOfThisPixel = rgb2hsv([r g b])
hsv(:, :, 1) = hsvOfThisPixel(1);
% Make the saturation 1 so we'll see color.
% Originally it was zero which meant that the image would be gray.
hsv(:, :, 2) = 1;
% Convert back to rgb space.
singleHueRGBImage = uint8(255*hsv2rgb(hsv));
% Display the new, single hue color image.
subplot(2, 2, 2);
imshow(singleHueRGBImage);
title('New, Single Hue Color Image', 'FontSize', fontSize);
message = sprintf('Done with demo.');
uiwait(msgbox(message));

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MATLAB: How to get a dithered color image

MATLAB: Convert grayscale to RGB

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