File size shrinks after adding IPTC keywords

[PhiloVance]

Hello all,

I'm trying to add IPTC data to some very old photos with XNView 2.40, and I notice that the updated file is 6 to 8k smaller than the original size (100-200k files). If anything, I would have expected the file size to increase a bit as a result of the addition, but not decrease!

Is this normal? I'm worried that the operation may not be "lossless."

Thanks for any insights.

[xnview]

please send me an original file?