How can I measure the rotation angle of one photo relative to another?
Asked 4/3/2017
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2 answers
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I have a series of photos of a mechanical device. In each image, a clearly marked part appears at a different rotation, and I need to measure that rotation in degrees for each file.
I tried auto-alignment tools in Photoshop and Hugin. They align the images visually, but I need a numeric result such as:
Image_001.jpg 0.5° Image_002.jpg 3.4° ...
Is there a practical way to extract or calculate the rotation angle of each image relative to a reference image?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
9y ago
2 Answers
4
If you have any experience with tools such as R or MATLAB , then all you need to do is load the image into the workspace, identify the centroid of your marker, and calculate the angle as
theta = atan(row_number/column_number)
In both R and MATLAB you can manually find the pixel that's at the centroid, by using locator() (R) or the coordinate-identifier tool in MATLAB. If your identifying item had a unique color, you could automate the search for its centroid. Or if you felt like getting fancy, you could do an automated search for its shape using a variety of "blob-matching" tools available. I suspect that's not going to be worth the effort in your case.
I'm interpreting your question as wanting just to know the rotation angle. If you actually need to rotate the images into alignment, I'd do that in one of your image-manipulation tools.
Originally by user25396. Source · Licensed CC BY-SA 4.0
user25396
9y ago
0
Generated from our catalog & community — verify before relying on it.
Yes, but the most reliable approach is usually to measure the feature itself rather than depend on an auto-align tool to report angle values.
If the marked element has a clear center and direction, you can identify its centroid (or another repeatable point/axis) and compute the angle from its image coordinates. In tools like MATLAB or R, this can be done manually or automated if the marker has a distinctive color or shape.
If you want to use Hugin, align_image_stack can generate a project file containing per-image parameters, and the r value in the image lines represents rotation. However, based on the community feedback, this may not always be reliable enough if you need precise measurements.
In practice, the best options are:
- detect the marker and calculate its angle directly from coordinates, or
- detect characteristic features, fit a line through them, and compare line angles between images.
So yes, a method exists, but for dependable degree measurements, direct geometric measurement of the marked part is preferable to relying only on stitching/alignment output.
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AI9y ago
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