how to convert color of a pixel gray to red

g=imread('f8');
rgb2gray(g);
imshow(g);

how to convert color of a pixel gray to red plzz

[Geoff Hayes]

abdel - don't you need to assign an output to rgb2gray like

g=imread('f8');
grayscaleImage = rgb2gray(g);
imshow(grayscaleImage);

As for converting a pixel gray to red...which pixel? what are the dimensions of grayscaleImage?

[abdel kader]

for any pixel

Answer 1

[Walter Roberson]

rgbimage = im2double( repmat(grayscaleImage, 1, 1, 3) );
rgbimage(some_row, some_column, 1) = 1;  %R
rgbimage(some_row, some_column, 2) = 0;  %G
rgbimage(some_row, some_column, 3) = 0;   %B

You can use the above with vectors of some_row and some_column as long as you want to change rectangular areas. If you have scattered row and column locations to set then

rgbimage = im2double( repmat(grayscaleImage, 1, 1, 3) );
[nrow, ncol, npane] = size(rgbimage);
idx = sub2ind([nrow, ncol], scattered_row, scattered_column);
rgbimage(idx + 0*nrow*ncol) = 1;   %R
rgbimage(idx + 1*nrow*ncol) = 0;   %G
rgbimage(idx + 2*nrow*ncol) = 0;   %B

[abdel kader]

not work

[Image Analyst]

Then use some_column instead of some_colum, and try not using im2double() and set red channel to 255 instead of 1.

[Walter Roberson]

The im2double and setting to 1 are there to avoid having to write code to figure out what the maximum value to write in should be, since we do not know cloass(grayscaleImage)

[Walter Roberson]

My code works for me with camerman.tif . The one thing to note is that if you imshow(rgbimage) then the red pixels might be difficult to notice, especially if it is against a lighter background (red on dark is easier to notice.) You might want to draw your image larger if you are using imshow().