C# Create gradient depending on color image

Question

I'm searching a C# way to create a color gradient depending on a image source. I found nothing on Internet but the goal is to reproduce what Instagram do with stories. For exemple from this: http://imgur.com/a/mWyF6mg To this: http://imgur.com/a/FnKnVWo

Thanks for your help

Answer 1

1. Resize picture wxh to column 1xh.
2. Resize column 1xh to background size.
3. (Gaussian blur)