Faster conversion of BGR packed to RGB planar pixel format

Question

From a SDK I get images that have the pixel format BGR packed, i.e. BGRBGRBGR. For another application, I need to convert this format to RGB planar RRRGGGBBB.

I am using C# .NET 4.5 32bit and the data is in byte arrays which have the same size.

Right now I am iterating through the array source and assigning the BGR values to there appropriate places in the target array, but that takes too long (180ms for a 1,3megapixel image). The processor the code runs at has access to MMX, SSE, SSE2, SSE3, SSSE3.

Is there a way to speed up the conversion?

edit: Here is the conversion I am using:

// the array with the BGRBGRBGR pixel data
byte[] source;
// the array with the RRRGGGBBB pixel data
byte[] result;
// the amount of pixels in one channel, width*height
int imageSize;

for (int i = 0; i < source.Length; i += 3)
{
    result[i/3] = source[i + 2]; // R
    result[i/3 + imageSize] = source[i + 1]; // G
    result[i/3 + imageSize * 2] = source[i]; // B
}

edit: I tried splitting the access to the source array into three loops, one for each channel, but it didn't really help. So I'm open to suggestions.

for (int i = 0; i < source.Length; i += 3)
{
    result[i/3] = source[i + 2]; // R
}

for (int i = 0; i < source.Length; i += 3)
{
    result[i/3 + imageSize] = source[i + 1]; // G
}

for (int i = 0; i < source.Length; i += 3)
{
    result[i/3 + imageSize * 2] = source[i]; // B
}

Bump because the question is still unanswered. Any advise is very appreciated!

Answer 1

You could try to use SSE3's PSHUFB - Packed Shuffle Bytes instruction. Make sure you are using aligned memory read/writes. You will have to do something tricky to deal with the last dangling B value in each XMMWORD-sized block. Might be tough to get it right but should be a huge speedup. You could also look for library code. I'm guessing you will need to make a C or C++ DLL and use P/Invoke, but maybe there is a way to use SSE instructions from C# that I don't know about.

edit - this question is for a slightly different problem, ARGB to BGR, but the techniques used are similar to what you need.

Answer 2

Basler company has a SDK for their cameras, called Basler Pylon, working in Windows and Linux.
This SDK has APIs for C++, C# and more.
It has an image conversion class PixelDataConverter, which seems to be what you need.