Fastest way to copy pixels from one bitmap to another?

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C#

Bitmap

Hi, I am using an algorithm to straighten images. A quadrilateral image is mapped into a rectangular image. I am able to compute a grid with pixel mapping defined at its each node. What i want is to find out an efficient way to copy the respective pixels into my rectangular image. I have tried Get and SetPixel methods of bitmap class which are too slow. Currently the solution i found uses lockbits method to copy chunks of source image into my destination image because simple lockbits method throws out of memory exception if the source image is too large.