Question

I am receiving an image from an external system in the form of a sequence of BGR values followed by an empty byte. The sequence looks sort of like…

[B,G,R,0,B,G,R,0,…,B,G,R,0] where each BGR0 is a single pixel in an image.

I need this in a .NET Bitmap so I can perform some manipulations on it and have come up with the following function to do so:

    private Bitmap fillBitmap(byte[] data, int width, int height)
    {
        Bitmap map = new Bitmap(width, height);
        for (int i = 0; i < data.Length; i += 4)
        {
            int y = ((i / 4) / width);
            int x = ((i / 4) - (y * width));
            int b = data[i];
            int g = data[i + 1];
            int r = data[i + 2];
            Color pixel = Color.FromArgb(r, g, b);
            map.SetPixel(x, y, pixel);
        }
        return map;
    }

This would normally be ok except that most of my images are 1920×1200… so I have a loop that’s iterating over 2 million times. Even then that wouldn’t be so bad as 2 million iterations shouldn’t be very taxing on any modern processor.

But for some reason, this loop can take upwards of 5-15 seconds to run on a pretty beefy Xeon on my server. It would be trivial to parallelize the loop but I suspect there is an even better way of going about this. Any help would be greatly appreciated!

Answer 1

The description of the Bitmap.LockBits Method says,

You can change the color of an image with the SetPixel method, although the LockBits method offers better performance for large-scale changes.

An alternative, I’d guess, might be to use the Bitmap(Stream) Constructor, after you create a Stream which matches the file format of a bitmap.