Intel® Integrated Performance Primitives
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Alpha composite onto destination without alpha


I have two cases where I need to do fast composition of images and I can't find a suitable method in IPP.

In both cases the destination image doesn't have an alpha channel, but I have alpha information for the image I'm trying to composite on top. I don't want to create an alpha channel in the destination image just for this operation because the ROI might be very small.

So my use cases are:

  • Destination image (background) is 8uC3, source image (on top) is 8uC4
  • Destination image (background) is 8uC3, source image (on top) is 8uC3 and I have another 8uC1 image containing its alpha.

One option which seems inefficient would be to copy the destination ROI into a new 8uC4 image, use AlphaComp with source image, then copy back to destination ROI.

Is there a nicer way to do this with existing IPP functions, or can someone recommend a fast way to code these operations, keeping the ROI functionality which would get vectorized well?

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