Does a ROM lose quality after compression?

[Grim Reaper]

I'm wondering, since bitmap images lose quality during compression does the images on a ROM lose quality as well or is it lossless?

[Lord Riff Raff]

Bitmap images don't lose their quality during compression. They lose their quality if you change the encoding format.
You can't use lossy compression on data or executable files.

[grantu2]

Think of data compression only "rearranges" data, no data is being thrown away. One bad thing that could happen in data compression is data corruption.

[Magus]

The most that will occur is that the compression algorithm will remove unnecessary and superfluous data that will not affect quality. It is still considered lossless.