MATLAB: Can i subtract 1 image from another by imsubtract()? i am having some errors in this case.

Image Processing Toolboximsubtract()subtracting images

i have generated 2 images, one by sobel operator and 1 by 1×2 operator. now i am trying to subtract the 1×2 operator applied image from sobel operator applied image. i used imsubtract() but it is not displaying the subtracted image. it is giving errors. can we use imsubtract() to only subtract arrays or we can also use it for subtractng images? please let me know.

grayImage= rgb2gray(rgbImage);
size(grayImage);
BW = edge(grayImage,'sobel',0.006);
filteredImage = conv2(double(grayImage), [-1 1], 'same');
subtractedImage = imsubtract(BW,filteredImage);
imshow(subtractedImage);
drawnow();

Best Answer

The values are likely very small for the 1x2 filter - like 0-20 or so. And the Sobel thresholded edge image has values of only 0 and 1. So subtracting almost anything at all from that (except subtracting zero) will clip to zero. So your image is most likely all zeros and displays as black. There may - slight chance - be some pixels that have a value of 1 and you can see those if they exist with the [] option to imshow():

imshow(subtractedImage, []);

But most likely there are no such 1 pixels. But the bigger question is why you are even doing this strange operation in the first place. I can see no theoretical reason why you'd want this subtraction in your algorithm - it's just worthless. Share your thought process so I can see if it makes sense or if what you want to do is better accomplished in some other way that does make sense.

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Is your sobel image the true sobel edge filtered image, or is it the thresholded, skeletonized image returned by edge()? If it's the latter, well, that has only two values. Is sobelImage uint8 or double? You can use cumsum() to find the top 5% of the pixels

cdf = cumsum(pixelCounts) / sum(pixelCounts);
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Convert to grayscale and then threshold and find the bounding box

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
imtool close all;  % Close all imtool figures.
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;
% Read in the color image.
folder = pwd;
baseFileName = 'm2.bmp';
% 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, numberOfColorBands] = size(rgbImage);
% Display the original color image.
subplot(2, 3, 1);
imshow(rgbImage, []);
axis on;
title('Original Color Image', 'FontSize', fontSize);
drawnow;
% Enlarge figure to full screen.
set(gcf, 'units','normalized','outerposition',[0 0 1 1]);
% Histogram the red channel, but there is a huge spike at 255 so let's not count those.
subplot(2, 3, 2);
grayImage = rgb2gray(rgbImage);
imshow(grayImage, []);
title('Gray Scale version', 'FontSize', fontSize);
subplot(2, 3, 3);
histogram(grayImage(grayImage<255))
grid on;
title('Histogram of Gray Scale Image', 'FontSize', fontSize);
someThresholdValue = 150;
binaryImage = grayImage > someThresholdValue;
% Take largest blob
binaryImage = bwareafilt(binaryImage, 1);
subplot(2, 3, 4);
imshow(binaryImage);
grid on;
title('Binary Image', 'FontSize', fontSize);
% Label the binary image.
labeledImage = bwlabel(binaryImage);
props = regionprops(labeledImage, 'BoundingBox');
bbox = props.BoundingBox
croppedImageRGB = imcrop(rgbImage, bbox);
subplot(2, 3, 5);
imshow(croppedImageRGB);
grid on;
title('Cropped RGB Image', 'FontSize', fontSize);
% Gray scale version of cropped image
croppedImageGray = imcrop(grayImage, bbox);
subplot(2, 3, 6);
imshow(croppedImageGray);
grid on;
title('Cropped Gray Scale Image', 'FontSize', fontSize);

Best Answer

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