It should return a slice of length dy, each element of which is a slice of dx 8-bit unsigned integers.
in my opinion would be better as
It should return a slice of length dy, each element of which is a slice of length dx of 8-bit unsigned integers.
Also
The choice of image is up to you. Interesting functions include (x+y)/2, x*y, and x^y.
is better to make clearer like
The choice of image is up to you. Interesting functions include (x+y)/2, x*y, and x^y, considering x and y are indexes of dy and dx slices. Use this as inner slice values.
Context: https://go.dev/tour/moretypes/18
I suggest to correct some wording
in my opinion would be better as
Also
is better to make clearer like