How to crop a region of interest in an image based on the area in pixels?

In the code below, I open and crop three images by selecting the four corners of the region of interest, which is a rectangular shape, but because it isn't perfect, a polygon is drawn.

clear varaiables, close all
if ~exist("subject_image_analysis.mlx")  % for development, if ROI already set, do not repeat
    % 1. Load the file and scale it 4:1 at each side
    before = "PIC_1596";  white = "PIC_1539"; after = "PIC_1601";
    A = imresize(imread(before,'jpg'),1.00);
    B = imresize(imread(white,'jpg'),1.00);
    C = imresize(imread(after,'jpg'),1.00);
    
    %     % 2. manually specify the ROI using the original image
    imshow(C)
    h = drawpolygon('FaceAlpha',0);
    h.Color = 'yellow';
    % find a bounding box of ROI to further cut the image smaller
    % bbox = [xmin ymin xmax ymax]
    hmin = min(h.Position); hmax = max(h.Position);
    bbox = [hmin hmax-hmin]; % 1x4 vector: upper left row and column indices, # rows, # cols of ROI
    %     3. Crop ROI for both image a and image b using the bounding box
    Cb = imcrop(B,bbox);  % ROI for image a
    Ca = imcrop(A,bbox);  % ROI for image b
    Cc = imcrop(C,bbox);
    % clear original images
    clear A B C
    save sqa.mat  % save these two ROIs andrelated parameters in a .mat file
else
    load sqa.mat
end

After this, I would like each image to be cropped further into 8 same sized rectangles (or regions). How can this be achieved using the area in pixels?

Ideally, this would look like 4 regions in the top half and 4 regions in the bottom half, so that each region can be further analyzed individually.

[Image Analyst]

Do you want to crop out and save the 1/8th image in 8 variables? Or a single cell array with 8 cells where each cell is one of the subimages? What are you going to do with these? Maybe you can just loop 8 times, extracting one subimage during each iteration and use it right away to compute something.

See the FAQ:

https://matlab.fandom.com/wiki/FAQ#How_do_I_split_an_image_into_non-overlapping_blocks?