MATLAB: Histogram within Minimum Bounding Box

bounding boxhistogramImage Processing Toolbox

How do I calculate the histogram within a minimum bounding box, along the orientation of the rectangle? Let say I have the coordinates of the four corners.

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Ignore my last answer since it doesn't look like you want "the histogram within a minimum bounding box" like you said first. The second part of your question looks like you really want the radon transform. To get the radon transform, look it up in the help. The radon transform is the sum of your image (the profile) as it's summed along a particular angle, which is what it sounds like you want.

I'm attaching a demo where I use the radon transform to rotate an image to align it with the raster lines.

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MATLAB: Drawing bounding box for the skew text regions

Use bwconvhull() and regionprops()

binaryImage = grayImage < 128; % Threshold.
joinedBlobs = bwconvhull(binaryImage, 'union'); % Get convex hull of all blobs.
props = regionprops(joinedBlobs, 'BoundingBox'); % Find bounding box.
boundingBox = props.BoundingBox; % Pull from field of structure into 1x4 vector.

You'll have to get rid of that outer black box first though so that you have ONLY the letters and not some frame or boundary.

To determine angle of skew, you might look at the radon transform. Demo attached.

MATLAB: How the Peak value of the image histogram can be obtaind

[pixelCounts, grayLevels] = imhist(grayImage);
[maxCount, indexOfMax] = max(pixelCounts);
grayLevelAtMax = grayLevels(indexOfMax);

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MATLAB: Drawing bounding box for the skew text regions

MATLAB: How the Peak value of the image histogram can be obtaind

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