What algorithm does the TinyPNG service use?

Question

Images

Greetings , I have been using the tinypng.com
service for a long time to reduce the weight of the image, as well as the ImageOptim desktop program, and, it seems, both of them do the job well, but sometimes, yes sometimes, there is almost always a difference when comparing files by weight between these services. Everything is clear in ImageOptim, the scripts used are specified in the settings: And with TinyPNG, everything is completely unclear - what compression algorithm do they use? One of your own or a third party?

Answer 1

They also write there:

By reducing the number of colors, 24-bit PNG files can be converted to much smaller 8-bit indexed color images.

They reduce color depth. As a matter of fact it turns out as gif with correctly picked up palette for the specific image.