Filesize changes whereas there is no change to the picture

[CheeseDurger]

Hi,
I'm trying to reduce image that are > to 1 MP. However, there are already multiple images < 1 MP in the input. And when the batch goes on, those images size stays the same (height and width - so far so good) but the file size changes... So why is it so ?

See, the example below : from 61,1KB to 35,2 KB. I tried the batch on jpg and png. Also, sometimes the filesize increases, and sometimes it decreases.

I searched the forums but couldn't go with anything (well, I confess I'm quite new to all of this).


Thanks.

[xnview]

In batch convert file are always resaved, resize action is not always executed...

[CheeseDurger]

In batch convert file are always resaved, resize action is not always executed...

Thanks for your answer. However, why would filesize change (up or down) if resize isn't executed ? Is image quality still the same ?

[xnview]

perhaps the compression mode for png is not the same

[CheeseDurger]

Ok.

I did a little test with the 2 PNGs (the original one and the one that got copied with XnConvert). I converted them to BMP with XnView then I did an hex comparison of the 2 image files. The BMP were exactly the same at the hex level. So I guess you're right and, for PNGs, it's just a matter of compression.

However, what about JPEG ? I did the same test, and the BMPs were different at the hex level.
Have you another wild guess for that ?

[xnview]

However, what about JPEG ? I did the same test, and the BMPs were different at the hex level.
Have you another wild guess for that ?

PNG is lossless compression, jpeg is lossy compression