How to find the (pixel) dimensions of images on a white background

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Hello there,
I have a folder of 60 images of irregular household items that are greyscale on a white 500x500 pixel canvas. I need to have the images rescaled (will do in photoshop) to match the average size of a different set of images. Using MATLAB, I found the references images have 1.51 times more non-white pixels (i.e. image pixels) than the items do and need to alter these images to match the size. However, because the images are of vastly different items (i.e. a paperclip vs a closet), they vary a lot by dark pixel count.
How can I find the dimensions (height and width) of these images in MATLAB. I've included an example of an image being
samplePic = imread(img_dir + "/hn_processed");
image_double = im2double(samplePic); % turn all white pixels to 1
% I tried the below code by it didn't do what I wanted
actual_image = find(image_double ~= 1);
[rows, columns, numberOfColorChannels] = size(actual_image);
used. Thank you!
  2 Comments
Adam Danz
Adam Danz on 8 Apr 2021
As long as the strawberry is oriented vertically or horizontally, the simple approach in my solution gives you to width and height.

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Accepted Answer

Adam Danz
Adam Danz on 6 Apr 2021
Edited: Adam Danz on 7 Apr 2021
Assuming height and width are defined by the first and last non-white (or any background color) pixel from top-to-bottom and from left-to-right,
I = imread('image.bmp');
% Assumes the first pixel is the background color,
% otherwise just use 255 or likewise.
[row,col] = find(I~=I(1));
height = max(row)-min(row);
width = max(col)-min(col);
To visually confirm the measurements,
imshow(I)
hold on
r = rectangle('position', [min(col), min(row), width, height],'EdgeColor', 'r');

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