Speed up Matrix Addition in C#

Question

I\'d like to optimize this piece of code :

public void PopulatePixelValueMatrices(GenericImage image,int Width, int Height)
{            
        for (int x = 0;         


        

Answer 1

This is a classic case of micro-optimisation failing horribly. You're not going to get anything from looking at that loop. To get real speed benefits you need to start off by looking at the big picture:-

• Can you asynchronously preload image[n+1] whilst processing image[n]?
• Can you load just the B channel from the image? This will decrease memory bandwidth?
• Can you load the B value and update the sumOfPixelValues(Squared) arrays directly, i.e. read the file and update instead of read file, store, read, update? Again, this decreases memory bandwidth.
• Can you use one dimensional arrays instead of two dimensional? Maybe create your own array class that works either way.
• Perhaps you could look into using Mono and the SIMD extensions?
• Can you process the image in chunks and assign them to idle CPUs in a multi-cpu environment?

EDIT:

Try having specialised image accessors so you're not wasting memory bandwidth:

public Color GetBPixel (int x, int y)
{
    int offsetFromOrigin = (y * this.stride) + (x * 3);
    unsafe
    {
        return this.imagePtr [offsetFromOrigin + 1];
    }
}

or, better still:

public Color GetBPixel (int offset)
{
    unsafe
    {
        return this.imagePtr [offset + 1];
    }
}

and use the above in a loop like:

for (int start_offset = 0, y = 0 ; y < Height ; start_offset += stride, ++y)
{
   for (int x = 0, offset = start_offset ; x < Width ; offset += 3, ++x)
   {
      pixel = GetBPixel (offset);
      // do stuff
   }
}