Object detection on an image with varying brightness

I want to isolate the greyish horizontal line located at the bottom half of the attached image. Thresholding is not working well since the lower part of the image is dark. I have tried adaptive mean threashold as well as canny edge detection but its not working.

unfortunately, it’s only mostly horizontal, not exactly horizontal, and I think I see some curve to it.

you can try summing up pixel rows for a stronger 1D signal. rotate the source image by various amounts and see where the response is clearest (steepest edges).

You can try answers from this old post object detection in nonuniform illumination - OpenCV Q&A Forum

This approach helped!

Thank you