Change Pixel in image - optimize code

Hi.

Im trying to loop through all the pixels of a thermal camera image i saved. i want to replace certain colors, lets say red with black pixels. the code below kinda works too, it just takes ages to complete (extremely long).

So my question is on how i could optimize it and make it all better. the function magic is the problem that takes so long

impath = "image.jpg";

image = imread(impath);

cropped = imcrop(image);
colors = [];

for i=1:size(cropped,1)        
    for a=1:size(cropped,2)
        %disp("crop data: " + cropped(i, a, 1) + " " + cropped(i, a, 2) + " " + cropped(i, a, 3));

        colors = [cropped(i, a, 1) + " " + cropped(i, a, 2) + " " + cropped(i, a, 3), colors];
    end
end

colors = unique(colors);
image = magic(image, colors, [0, 0, 0]);
imshow(image);


function result = magic(image, rgb, target)
    for i=1:size(image,1)
        
        for a=1:size(image,2)

            for b=1:size(rgb, 2)

                t1 = reshape(uint8([str2num(rgb(b))]), 1, 1, 3);
                t2 = reshape(image(i, a, :), 1, 1, 3);


                if reshape(image(i, a, :), 1, 1, 3) == reshape(uint8([str2num(rgb(b))]), 1, 1, 3)
                   image(i, a, :) = target;
                   disp("yes");
                end
            end

        end
    
    end

    result = image;

end

Answer 1

[Image Analyst]

Try the Color Thresholder on the Apps tab of the Tool ribbon. Use LAB color space.

% Converts RGB image to LAB colorspace, then changes red to black.
clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables. Or clearvars if you want.
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 20;
% Check that user has the Image Processing Toolbox installed.
hasIPT = license('test', 'image_toolbox');   % license('test','Statistics_toolbox'), license('test','Signal_toolbox')
if ~hasIPT
    % User does not have the toolbox installed.
    message = sprintf('Sorry, but you do not seem to have the Image Processing Toolbox.\nDo you want to try to continue anyway?');
    reply = questdlg(message, 'Toolbox missing', 'Yes', 'No', 'Yes');
    if strcmpi(reply, 'No')
        % User said No, so exit.
        return;
    end
end
%===============================================================================
% Read in a standard MATLAB color demo image.
folder = fileparts(which('peppers.png')); % Determine where demo folder is (works with all versions).
baseFileName = 'peppers.png';
% Get the full filename, with path prepended.
fullFileName = fullfile(folder, baseFileName);
if ~exist(fullFileName, 'file')
    % Didn't find it there.  Check the search path for it.
    fullFileName = baseFileName; % No path this time.
    if ~exist(fullFileName, 'file')
        % Still didn't find it.  Alert user.
        errorMessage = sprintf('Error: %s does not exist.', fullFileName);
        uiwait(warndlg(errorMessage));
        return;
    end
end
rgbImage = imread(fullFileName);
% Get the dimensions of the image.  numberOfColorBands should be = 3.
[rows, columns, numberOfColorChannels] = size(rgbImage);
% Display the original color image.
subplot(2, 1, 1);
imshow(rgbImage);
axis on;
title('Original Color Image', 'FontSize', fontSize, 'Interpreter', 'None');
% Mask out the red pixels.
[mask, maskedRGBImage] = createMask(rgbImage);
% Display the masked image where red is now black.
subplot(2, 1, 2);
imshow(maskedRGBImage);
hp = impixelinfo();
title('Masked Image', 'FontSize', fontSize, 'Interpreter', 'None');

%=================================================================================================
function [BW,maskedRGBImage] = createMask(RGB)
%createMask  Threshold RGB image using auto-generated code from colorThresholder app.
%  [BW,MASKEDRGBIMAGE] = createMask(RGB) thresholds image RGB using
%  auto-generated code from the colorThresholder app. The colorspace and
%  range for each channel of the colorspace were set within the app. The
%  segmentation mask is returned in BW, and a composite of the mask and
%  original RGB images is returned in maskedRGBImage.
% Auto-generated by colorThresholder app on 19-Dec-2022
%------------------------------------------------------
% Convert RGB image to chosen color space
I = rgb2lab(RGB);
% Define thresholds for channel 1 based on histogram settings
channel1Min = 1.844;
channel1Max = 100.000;
% Define thresholds for channel 2 based on histogram settings
channel2Min = -56.604;
channel2Max = 16.859;
% Define thresholds for channel 3 based on histogram settings
channel3Min = -64.147;
channel3Max = 94.387;
% Create mask based on chosen histogram thresholds
sliderBW = (I(:,:,1) >= channel1Min ) & (I(:,:,1) <= channel1Max) & ...
    (I(:,:,2) >= channel2Min ) & (I(:,:,2) <= channel2Max) & ...
    (I(:,:,3) >= channel3Min ) & (I(:,:,3) <= channel3Max);
BW = sliderBW;
% Initialize output masked image based on input image.
maskedRGBImage = RGB;
% Set background pixels where BW is false to zero.
maskedRGBImage(repmat(~BW,[1 1 3])) = 0;
end

[Marcel]

sadly it wont really work cauz the colors used in the thermal picture and the "color range bar" for indication are not the same so its not really accurate. Issue of the camera.

[Image Analyst]

Well I don't know how you got a pseudocolored thermal camera image with a different colorbar than was actually used to pseudocolor the image.

But for what it's worth, attached is a demo for how to convert a pseudocolored thermal camera image into a temperature image providing you know what temperature the ends of the colorbar represent.

[Marcel]

Well the camera is from Mobotix. Its kinda strange but it works when you add a lot more colors, tho this comes with inaccuracy sadly.

[Image Analyst]

Can you attach those two images?

[Marcel]

Hi im sorry im not in the office for the next 6 months, therefore dont have my company computer and no matlab license as well as the images etc :c