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### What is the best way to approximate a contour with a warped rectange?

I have some images containing plates and each image has a file that contains a list of points around the plate. The points were chosen manually by some persons, so there is no rule (like chose the four corners or something like that). I want to extract the plates from the images, but I have met some problems in choosing the best approach for finding the closer quadrilateral that describes the plate.

I have tried to do a minAreaRect on the contour, but his is often returning a very different quadrilateral that has a lot of background and/or the plate is inclined (like italic) in some direction.

I have tried to do approxPolyDP and it seems that it returns a much more close contour (that is expected to be so), but here the problem is about the approximation error (epsilon): if it is too small, I get a contour that has more than 4 corners; if it is too large, I may receive a contour that has 3 corners, or that has cut a part of the plate. [I have tried to apply here the minAreaRect on those cases, but it seems that I arrive in the same situation as in the first try]

I am willing to apply the approxPolyDP in a recursive mode: if the approximation has not 4 corners I will increase the error and apply once more the function. But is this the way to go? Isn't there a function that may approximate the contour with the closest quadrilateral? Or is there another suggestion in achieving this?

 2 retagged sturkmen 6021 ●3 ●42 ●69 https://github.com/stu...

### What is the best way to approximate a contour with a warped rectange?

I have some images containing plates and each image has a file that contains a list of points around the plate. The points were chosen manually by some persons, so there is no rule (like chose the four corners or something like that). I want to extract the plates from the images, but I have met some problems in choosing the best approach for finding the closer quadrilateral that describes the plate.

I have tried to do a minAreaRect on the contour, but his is often returning a very different quadrilateral that has a lot of background and/or the plate is inclined (like italic) in some direction.

I have tried to do approxPolyDP and it seems that it returns a much more close contour (that is expected to be so), but here the problem is about the approximation error (epsilon): if it is too small, I get a contour that has more than 4 corners; if it is too large, I may receive a contour that has 3 corners, or that has cut a part of the plate. [I have tried to apply here the minAreaRect on those cases, but it seems that I arrive in the same situation as in the first try]

I am willing to apply the approxPolyDP in a recursive mode: if the approximation has not 4 corners I will increase the error and apply once more the function. But is this the way to go? Isn't there a function that may approximate the contour with the closest quadrilateral? Or is there another suggestion in achieving this?

### What is the best way to approximate a contour with a warped rectange?

I have some images containing plates and each image has a file that contains a list of points around the plate. The points were chosen manually by some persons, so there is no rule (like chose the four corners or something like that). I want to extract the plates from the images, but I have met some problems in choosing the best approach for finding the closer quadrilateral that describes the plate.

I have tried to do a minAreaRect on the contour, but his is often returning a very different quadrilateral that has a lot of background and/or the plate is inclined (like italic) in some direction.

I have tried to do approxPolyDP and it seems that it returns a much more close contour (that is expected to be so), but here the problem is about the approximation error (epsilon): if it is too small, I get a contour that has more than 4 corners; if it is too large, I may receive a contour that has 3 corners, or that has cut a part of the plate. [I have tried to apply here the minAreaRect on those cases, but it seems that I arrive in the same situation as in the first try]

I am willing to apply the approxPolyDP in a recursive mode: if the approximation has not 4 corners I will increase the error and apply once more the function. But is this the way to go? Isn't there a function that may approximate the contour with the closest quadrilateral? Or is there another suggestion in achieving this?

After many requests, I finally add the images.

Supposing I have an image like this or like this one . Do a simple binarization to find some plates contour. It should have many points, and especially on the corners there are more than one point. If you do something interesting, please let me know :)