[saagarjha]

Instead of doing a memset, I'd recommend using std::fill (which will likely call memset or another fast implementation behind the scenes): it makes it clear what you are doing, and preempts questions of "is this legal to do" (which it is, but only for POD data types).

[marcianx]

I'm far more inclined toward

  img.assign(w*h, color);

myself.

[saagarjha]

Normally I choose the methods in <algorithm> because they take an ExecutionPolicy parameter, allowing me to make this code parallel if I wish, but both are valid.