Replace System.Drawing with ImageSharp

[Poker-sang]

For greater efficiency and better cross-platform.

[d-franklin]

There are still issues with the code. I've fixed an issue with the regions being the incorrect size and location and I'm working on fixing another issue related to actual detection.

Just a heads up for anyone looking to run yolov5-net on a non-windows platform and is looking at this pull for a possible solution.

[Poker-sang]

There are still issues with the code. I've fixed an issue with the regions being the incorrect size and location and I'm working on fixing another issue related to actual detection.

Just a heads up for anyone looking to run yolov5-net on a non-windows platform and is looking at this pull for a possible solution.

I am sorry that there's still a problem. It seems like the predict rectangle, is based on the resized input image, but not based on the original one. So I think the simplest fix for this is to resize the predict rectangle again.

[Poker-sang]

Now I fix the bug that made predict rectangle distorted, through removing the code below:

var gain = Math.Min(xGain, yGain); // gain = resized / original

Now I thought it can behave just like the main repository.

[d-franklin]

There is still bugs in this code, I ran out of time so I couldn't fix them and I haven't touched it in 6 months so I can't remember what unfortunately, but they are there.

[kkarahainko]

bugs are always there ) no worries, thanks for contribution!