MATLAB matrix strange operation

I've been trying to convert MATLAB code to python and found this line of code which looks weird to me:

S = favg(I+1);

Where favg is a 256-by-1 matrix, I is a 512-by-512 matrix and the result S is a 512-by-512 matrix.

Can anybody help me understand what S is? Thanks.

Answer 1

[DGM]

Conceptually, I would have no idea what S is, since I don't know what I or favg are with essentially zero context.

As far as the operation goes, I would assume that I is an array of linear indices into favg. So the values within I should be in the range [0 255]. I'll guess that the +1 offset is because the array is uint8. Again, I can only guess. It would seem odd that favg would only have one channel if it were a color table.

If this were indeed some sort of indexed image operation (or something analogous), then that would probably make I the indexed image and S the grayscale image.

How's that for a guess?