nQuant | nQuant is a .NET color quantizer producing high quality | Computer Vision library

I am using AspnetBoilerplate. After much trial and error I found that it was something in the OWIN integration in ABP that caused the Imageresizer module to not run in the case in question. As I'm not using the OWIN part of ABP I simply turned it off by removing this line:

Startup.cs:

Your code as it stands uses a single thread to handle each of your rows separately. As a result you are starving for quick scratch memory (registers, L1 cache, shared memory). You are allocating at least 1600 bytes per each thread - that is a lot! You want to stay at around 128 bytes per thread (32 registers of 32 bits each). Secondly, you are using local arrays addressable at run-time -- those arrays will be spilled into local memory, trash your L1 cache and end up in global memory again (1600B x 32 threads gives 51KB, which is already at or above the limits of shmem/L1).

For that reason I would suggest handling a single row per block of 64 or 128 threads instead, and keep the row you sort in shared memory. Bubble sort is actually very easy to implement in parallel:

Your code just concatenates content of these images to one file as you are not resetting position in the file stream.

But it is bad idea to use one stream. If your new file is smaller than old, your result will be broken as file will not be resized to smaller size.

Use temp files instead.