Where is `gradient.png`?

[pengyu]

I don't find the raw image of gradient.png.

https://github.com/abidrahmank/OpenCV2-Python-Tutorials/blob/master/source/py_tutorials/py_imgproc/py_thresholding/py_thresholding.rst

The image directory has a file called gradient.png, but it is just the result image, not the input image.