Why does Topaz Photo AI reduce the size of JPEGs?

Just got Photo AI, it’s already paid for itself by saving a handful favourite older photographs that suffered from one of the defects it is designed to correct. Thank you!

My question is: why are the JPEGs it outputs from the JPEGs I feed into it more or less 1/2 to 1/3 the original size in MB? Where’s all that data going?

jpeg is not a lossless format, by design the format varies in the quality of saves trading off for the size of the file. The intent of that is it will be lost in your eye anyways and sometimes a compressor can save space and you would never notice the difference other times you waste space yet still notice the difference. It varies depending on the images.

jpeg should not be used for an archival format if you plan on future edits.