# Overlay gray ROI on an image

3 views (last 30 days)
Ely Raz on 15 Jan 2022
Commented: Walter Roberson on 15 Jan 2022
Based on this question (https://www.mathworks.com/matlabcentral/answers/1620785-overlay-roi-on-an-image) and one of the answers (@Image Analyst), I can not overlay the grayRoi on the rgbImage as the outcome image as some colors where it should be gray. How can I solve it?
Code:
close all;
clear all;
clc;
figure('Name','Sevilla');
imshow(rgbImage)
axis('on', 'image')
uiwait(helpdlg('Draw a rectangle'))
roi = drawrectangle('StripeColor','r')
pos = roi.Position
% OPTIONAL Get rid of graphical overlay and replace with yellow rectangle.
delete(roi)
rectangle('Position', pos, 'EdgeColor', 'y', 'LineWidth', 2);
% Crop image using indexing.
col1 = floor(pos(1)); % Column 1
col2 = ceil(pos(1) + pos(3)); % Column 2
row1 = floor(pos(2)); % Row 1
row2 = ceil(pos(2) + pos(4)); % Row 2
GrayRoi = rgb2gray(rgbImage(row1 : row2, col1 : col2, :));
figure
imshow(GrayRoi)
axis('on', 'image')
newI = rgbImage;
newI(row1 : row2, col1 : col2) = GrayRoi;
figure
imshow(newI)

Walter Roberson on 15 Jan 2022
newI(row1 : row2, col1 : col2) = repmat(GrayRoi, [1 1 size(newI,3)]);
##### 2 CommentsShowHide 1 older comment
Walter Roberson on 15 Jan 2022
newI(row1 : row2, col1 : col2, :) = repmat(GrayRoi, [1 1 size(newI,3)]);

R2020b

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