How to add a border around

I have two images like this. (image A, B)

I want to (1) overlap the figures and (2) fit a border around the areas of different color.

; as image C with 'red line around dark red area' and 'blue line around the light red area'.

I am unsure how to use the image proccessing toolbox to draw a borderline.

Answer 1

[Image Analyst]

For each image, convert to hsv color space with rgb2hsv. Untested code follows. Adapt/fix as needed.

hsvImage1 = rgb2hsv(rgbImage1);
hsvImage2 = rgb2hsv(rgbImage2);

Then create binary masks by thresholding the s channel to get regions that are not pure gray.

sImage1 = hsvImage1(:, :, 2);
mask1 = sImage1 > 0;
sImage2 = hsvImage2(:, :, 2);
mask2 = sImage2 > 0;

Then call bwboundaries

boundaries1 = bwboundaries(mask1);
boundaries2 = bwboundaries(mask2);

Then blend the images however you want to do it, for example by taking the average or other ways.

blendedImage = uint8((double(rgbImage1) + double(rgbImage2))/2);
imshow(blendedImage);

Then plot the boundaries over the blended image:

% Plot boundaries1 over the image.
for k = 1 : length(boundaries1)
    thisBoundary = boundaries1{k};
    x = thisBoundary(:, 2);
    y = thisBoundary(:, 1);
    hold on;
    plot(x, y, 'm-', 'LineWidth', 2);
end
% Repeat for boundaries2
% Plot boundaries2 over the image.
for k = 1 : length(boundaries2)
    thisBoundary = boundaries2{k};
    x = thisBoundary(:, 2);
    y = thisBoundary(:, 1);
    hold on;
    plot(x, y, 'm-', 'LineWidth', 2);
end