How to do af::replace based on col_index?

[Joe Chan]

Assume I have an array "a" with dim4 = h, w, c, 1

I want to assign blue color when column index is smaller than w/2

something like below

array out = af::replace(a, a.col < w/2, (255,0,0));

But how?

[Umar Arshad]

Try:

Assuming RGB:

a(seq(w/2), span, 2) = 255: