Fastest Way To Loop Through Every Pixel

[Chaos]

nikie wrote:
> Chaos wrote:
>
> > As my first attempt to loop through every pixel of an image, I used
> >
> >         for thisY in range(0, thisHeight):
> >             for thisX in range(0, thisWidth):
> >                   #Actions here for Pixel thisX, thisY
> >
> > But it takes 450-1000 milliseconds
> >
> > I want speeds less than 10 milliseconds
>
> Milliseconds don't mean much unless we knew how big your images are and
> what hardware you're using.
>
> Have you considered using NumPy? Assuming you can get the image into a
> numpy array efficiently, the actual algorithm boils down to something
> like this:
>
>     grey = r*0.3 +

 g*0.59 + b*0.11
>     index = grey.argmin()
>     x,y = index%step, index/step
>     v = grey[x,y]
>
> where r,g,b and grey are numpy.ndarray objects; The arithmetic
> operators and the argmin-function are implemented in C, so you can
> expect decent performance. (the 4 lines above take about 80 ms for a
> 1000x1000 image on my PC)
>
> If that's not enough, you might want to use some specially optimized C
> library for this purpose. (I'd suggest Intel's IPP, but there are
> others).

I really do not understand the code. Where did you get the varibales r,
g, b and step and what does v produce?