Hi all!

I’m currently using Evision and Nx in some computer vision applications. In my current scenario, I have an image which has a rectangular shape somewhere inside the image, and the background is black. I’d like to crop the image to just the rectangular shape. While I know I could use more advanced methods to detect the location of the rectangle (not the focus of this question), one simple one is just to sum along the rows and columns to find the rows/cols with non-zero values. Then, you can just crop the image to only include the specified rows and columns. The python code to do this is below

```
import numpy as np
import cv2
image = cv2.imread("image.png")
image_norm = np.linalg.norm(image, axis=2)
rows_sum = np.sum(image_norm, axis=1)
use_rows = np.argwhere(rows_sum > 0).ravel()
cols_sum = np.sum(image_norm, axis=0)
use_cols = np.argwhere(cols_sum > 0).ravel()
image_cropped = image[use_rows[:, np.newaxis], use_cols[np.newaxis, :]]
cv2.imwrite("output.png", image_cropped)
```

I had to fallback to Python to do this, because I couldn’t figure out how to do the `argwhere`

operations in Nx. Is this feature available currently? Is there an alternative that I’m not considering?

Looking for a pointer in the right direction.

Thanks and happy new year!

Gus