I’m using nppiDivC_32f_C4IR in an infinite impulse response filter. A buffer is divided, using the function, by {1, 1, 1, alpha_scale} before being composited using nppiAlphaComp_32f_AC4R with NPPI_OP_ALPHA_OVER to create a trail-off in the image. The alphas my vary across each image and vary from image to image. The result should be a slow trail off on moving objects. My problem is that the divide seems to be dividing the colour as well as the alpha as I’m getting a fade to black before the fade to transparency.
I’m investigating as I type but I suspect my problem either lies in the divide affecting the colour (though I doubt this from some playing), the alpha compose possibly pre-multiplying (which I don’t believe it should) or some other little technicality. I’d be grateful if anyone has any thoughts or can clarify what exactly nppiAlphaComp_32f_AC4R is doing.
Many thanks,
James