MATLAB: How to create a color mask on RGB jpeg image,which changes pixels with a specific range of RGB to a solid colour of choice

Question

I am trying to create a mask for an RGB jpeg image. The purpose of this mask needs to be to isolate pixels within a certain range of values for R, G and B channels (i.e., for 50<R<60, 40<G<45, and 31<G<32 – or something like this. I do not know how to isolate the range of values). I then need to replace the pixels that meet this criteria with a specific, solid color. The end goal is to create a habitat map by isolating pixels of certain reflectance values. So far, I have only been able to replace selected pixels with the color Black.

How can I:

a) select pixels within a RANGE of R G and B values,

and b) replace those pixels with any chosen colour?

Thank you so much for any help!

This is my attempted code:

myfile = 'myfile.jpg';

data=imread(myfile);

blue = squeeze(data(:,:,3)); % rgB

green = squeeze(data(:,:,2)); % rGb

red = squeeze(data(:,:,1)); % Rgb

% To look at the image and select which pixels to show:

imshow(data)

%% Mask pixels of certian RGB values

wrack_mask = (data(:, :, 3) > 100) & (data(:, :, 2) > 100) & (data(:, :, 1) > 100);

% need to select a range, not just > 100

% trying to mask the image bsxfun() function, but this only yields a black mask

maskedWrack = bsxfun(@times, data, cast(wrack_mask, 'like', data));

imshow(MaskedWrack)

…and this is the result:

Answer 1

I seem to have solved it by using imoverlay, and adding more terms to the data selection:

lf;

wrack_mask = (data(:, :, 3) > 49) & (data(:, :, 3) < 83) & (data(:, :, 2) > 35) & (data(:, :, 2) < 67) & (data(:, :, 1) > 18) & (data(:, :, 1) > 48);

dkred = [0.7 0.2 0.1];

MaskedWrack = imoverlay(data,wrack_mask,dkred);

imshow(MaskedWrack)