Resize mask should not use nearest method of opencv

I’m using this project to train my segmentation model. I find that the mask has a right-down offset to the image. Because the opencv resize_nearest is wrong. Please refer the opencv project issue:
https://github.com/opencv/opencv/issues/9096 https://github.com/opencv/opencv/issues/10146

The code of opencv is: for( x = 0; x < dsize.width; x++ ) { int sx = cvFloor(x*ifx); x_ofs[x] = std::min(sx, ssize.width-1)*pix_size; } It’s not the nearest, so it will be a offset between image and mask.

Mask uses the resize nearest in Pillow has no offset to the image. Using the resize nearest of opencv to train segmentation model will have a bad result.

[creafz]

I do agree that we need a way to fix the current behavior of OpenCV’s nearest interpolation that we use for masks.

However, we need a way to inform the current users of different behaviors of cv2.INTER_NEAREST and cv2.INTER_NEAREST_EXACT and let them choose the one they prefer. By following this path, we will not introduce a sudden significant change that will break the current behavior of augmentation pipelines (even if the current behavior is not optimal and may be seen as ‘buggy’, it is still how Albumentations resizes masks since the first release).

So my proposal is the following:

1. Add a way for users to specify the interpolation algorithm for masks. For example, we could use a parameter for A.Compose, e.g.

transform = A.Compose([...], mask_interpolation=cv2.INTER_NEAREST_EXACT)

1. In the nearest (no pun intended) release of Albumentations, add a warning which says that the next release will use cv2.INTER_NEAREST_EXACT instead of cv2.INTER_NEAREST for mask interpolation, and to preserve the old behavior, the user must explicitly specify the mask interpolation method for an augmentation pipeline. Let’s make a separate article in the documentation that tells the difference between those interpolation methods.
2. After that, in a new release, we will change the default interpolation method to cv2.INTER_NEAREST_EXACT, but still, show a warning if the user didn’t specify the interpolation method and Albumentations used the default value.

[karthik1145]

Can I try to fix it?

On Tue, Aug 17, 2021, 10:20 PM Mikhail Druzhinin @.***> wrote:

Unfortunately, this issue has not been fixed yet.

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