how to convert from grayscale to rgb by lightness method ??

how to convert from grayscale to rgb by lightness (desaturation) method (matlab code)??

[Turlough Hughes]

What have you tried so far?

[Hanan Elsayed]

This is my last attempt, but it didn't work

i=imread('peppers.png');

for j=1:size(i,1)

for k=1:size(i,2)

if i(j,k,1)>i(j,k,2)&&i(j,k,3)

max=i(j,k,1);

elseif i(j,k,2)>i(j,k,1)&&i(j,k,3)

max=i(j,k,2);

else

max=i(j,k,3);

end

if i(j,k,1)<i(j,k,2)&&i(j,k,3)

min=i(j,k,1);

elseif i(j,k,2)<i(j,k,1)&&i(j,k,3)

min=i(j,k,2);

else

min=i(j,k,3);

end

newimage=(max+min)/2;

end

end

imshow(newimage);

Answer 1

[Turlough Hughes]

You can do the following:

I=imread('peppers.png');

newImage = uint8(( double(min(I,[],3)) + double(max(I,[],3)) ) ./ 2);
imshow(newImage)

[Hanan Elsayed]

Thank you so much

[Turlough Hughes]

The original image has the following dimensions

size(imread('peppers.png'))

ans = 1×3

384 512 3

which is a 3D matrix of values that define the image. The third dimension has 3 pages, one for each colour stream; R, G and B.

In this case, they are values between 0 and 255 representing the R,G,B intensity.

max(I,[],3)

gives the max from the R,G and B intensitites and similarly for the entire image, I, while

min(I,[],3)

gives the min. Note, the outputs for the two previous function calls are arrays of size 384 by 512.

You can add the results of these arrays together using the + operator alone, however in order to divide you need to specify element-wise division which is where the ./ comes from.

[Image Analyst]

As you can plainly see, this doesn't work. The bright areas are clipped at 128. I'm giving @Turlough Hughes a chance to fix it.

[Turlough Hughes]

Thanks @Image Analyst. I should have converted to a datatype not capped at 255 in order to add the values. I've edited the answer with the correction.

Actually, one could also just do the following without converting datatypes:

I=imread('peppers.png');
newImage = min(I,[],3)./2 + max(I,[],3)./2;
imshow(newImage)

[Hanan Elsayed]

Thank you, I benefited a lot 💜💜💜💜