I am looking for a simple c# jpeg encoder that takes Color / Color32 array as input and returns jpeg byte.I once could find such snippet, but all I can find now is dependent on some framework.
I am trying to solve the problem with built-in ImageConversion class only working on the main thread
Well JPEG compression is not that simple therefore your requirement for a simple encoder is hard to fulfill ^^. To get a bit of a clue on the complexity I recommend watching the computerphile series on JPEG compression which is actually pretty good. Though the most difficult part (how to actually compute the discrete cosine tranform) is not really explained ^^.
For a possible solution, see this codeproject. Keep in mind that this is distributed under the CodeProject Open License so make sure you read it. Though the usage of the code shouldn’t be an issue,