interlacing/de-interlacing optimizations in image data

Hi,
I am trying to arrive at an efficient and optimized algorithm to
interlace/de-interlace pixel data in an image. The normal methods of
converting RGBRGB... order into RRRGGGBBB are heavily dependent on the
image size and the performance is very slow for large images.

Can somebody suggest ways to do this without using STL or assembly
code? preferably in c code.

The solution i am looking for must be a single buffer method, meaning
there shuldnt be a temp buffer and the performance shuld degrade at the
most linearly with image size.

since i have just had a few hrs to study the problem, ill spend some
time on it myself, but please feel free to give ur suggestions and
opinions on this matter.

all inputs r welcome

siddharth

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