How can i paint some pixels in grayscale image to non-gray colors?

I have a Grayscale images I want to paint some pixels pixels that i choose in red for example. How can i do it?

Answer 1

[Walter Roberson]

You cannot paint some pixels a non-gray color but have it remain a grayscale image.

You can overlay a different image on top that is transparent except where you want the colored pixels, and have the color in that second image. The color would have to be specified as RGB.

You can convert the image from grayscale to RGB and then replace pixels in the new image. For example,

RGBimage = cat(3, GrayImage, GrayImage, GrayImage);
RGBimage(1:10, 1:10, 1) = 255;
RGBimage(1:10, 1:10, 2:3) = 0;

and then display RGBimage

[David]

I am using MRI data and need to highlight portions. Using cat completely distorted the image. Do you have another suggestion in how to fix this?

[Walter Roberson]

I speculate that your MRI data is grayscale 3D, with the third dimension representing slices.

How are you displaying the data?