Why are converted files smaller than original when Output 'Format' is set to 'Original'?

[tjs]

I'm using XnConvert to add a date stamp to the bottom corner of my photos. When converting a jpeg photo taken on my smartphone, the output is about 1/2 the size of the original even though "Output Format" is set to "Same as Original".

For example, i started with a jpg file that is 3.64MB, 4032x2872px /24bit. I then added the time stamp with a Text Action. The resulting file is only 1MB with the same properties!? What is being removed/ compressed?

If anyone knows, please explain. Thank you.

[cday]

'Same as original' sets the output file format, but the compression used when saving is determined by the values set in the 'Settings...' button below...