It looks like this binary searches across the Go quality levels to find acceptable quality. This isn't a bad idea, but it won't be fruitful. The Go standard library JPEG encoder is pretty basic, and reuses the quant tables from the spec. It also doesn't optimize the huffman tables, so the pics are typically 10% bigger than they need to be.
This idea, taken to the extreme is mozjpeg. It is really advanced and can take advantage of a lot of cool tricks (like trellis optimization) in order to get the absolute best quality for the size.
This idea, taken to the extreme is mozjpeg. It is really advanced and can take advantage of a lot of cool tricks (like trellis optimization) in order to get the absolute best quality for the size.
https://github.com/mozilla/mozjpeg