How to Correctly Use cv::warpPerspective for Image Deskewing?

How to Apply cv::warpPerspective for Deskewing a Set of Points

When performing a perspective transformation on a set of points to achieve a deskewing effect, it's crucial to understand the proper organization of the points and the appropriate use of cv::getPerspectiveTransform.

Ensuring Correct Point Order

The points representing the corners of the ROI must follow a specific order in both the source and destination vectors. For example, if the source points are arranged as (top-left, bottom-left, bottom-right, top-right), the destination points must also follow this order.

Setting Image Size

To ensure the resulting image only contains the object of interest, set its width and height to match the width and height of the rectangular bounding box around the ROI.

Using Affine Transformations for Efficiency

For affine transforms (rotate, resize, deskew), it's more efficient to use the functions getAffineTransform and warpAffine. These functions expect only three points and a 2-by-3 matrix instead of a 3-by-3 matrix.

Setting Destination Image Size

To create a destination image with a different size than the input, use the following syntax in cv::warpPerspective:

cv::warpPerspective(src, dst, dst.size(), ... );

or use the following syntax in cv::warpAffine:

cv::warpAffine(src, rotated, warpAffineMatrix, size, INTER_LINEAR, BORDER_CONSTANT);

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