Python Opencv Region Of Interest Code Organization Problem

Each frame, like an image, then breaks down into pixels stored in rows and columns within the framepicture.

Each pixel has a coordinate location, and each pixel is comprised of color values.

Lets work out some examples of accessing various bits of these principles.

In the next tutorial, were going to cover some more advanced image operations that we can perform.

My ROI is rectangular, but I would like to make a custom shape as in the figure.

You can then use a mask (created with for instance MS Paint) to black out everything outside of the custom shape.

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Python Opencv Region Of Interest Code Organization Problem

This isnt so much a computer vision problem as a code organization problem.

This technique is especially helpful if you are labeling data as input to an image classification algorithm.

Open up a new file, name it clickandcrop.py, and well get to work.

Anytime a mouse event happens, OpenCV will relay the pertinent details to our clickandcrop function.

If it was, we record the (x, y) -coordinates of the event and indicate that we are now in cropping mode.

After we are done dragging out the region, we release the left mouse button Line 22 handles when the left mouse button is released and updates the list of points containing our ROI.

We also draw the rectangle representing the ROI on Lines 29 and 30.

We need only a single switch here, --image, which is the path to the image we want to crop.

We make a deep copy of the image so we can draw the rectangular bounding box on Line 29 without destroying the original image.

We first call cv2.namedWindow to create a window named image.

And we then set the mouse callback by calling cv2.setMouseCallback, supplying our named image window and our clickandcrop callback function.

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I did note, that if the bounding box was drawn starting from the right, moving left; it would not work.

To eliminate this, with a little research, I added a line to draw the rectangle using the coordinates first ordered by the minimum x,y values- which would be the top left of the box, and got the lower right by subtraction.

The best I could get here was to see a number of boxes growing larger as I moved the mouse none of which disappeared, so I had a bunch of boxes on the finished image.

The cropping still worked great, so the multiple boxes are a riddle for another day I am working with the opencv grabcut code which uses mouse movements to capture coordinates- and it draws a box nice and smooth.

I wanted to draw a nice smooth rectangle around the region, but I ended up with multiple rectangles drawn on the image, exactly like in your case.

However, when I do this the real-time drawing of the box did not perform as before.

The box still get drawn after I release my mouse-click, but it is not as cool as a real-time drawing of the box.

I havent had a chance to merge it into the repository yet, but it looks like what youre trying to accomplish.

Tricky problems with simple,straightforward but efficient solutions.

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