unexplained difference Photoshop-Gimp PNG filesize

[rich2005]

You have to make sure you are comparing like-with-like. First try and I got a scaled down Gimp png slightly smaller file size than the corresponding PS png.

To get something a third of the file size are you using PS settings like this? screenshot: https://i.imgur.com/4lfNdKz.jpg

Check in Gimp the file properties. Are they exactly the same in both versions? Using PS PNG8 the image is indexed with 256 colours rather 64000-ish.
Use Image -> Image Properties screenshot: https://i.imgur.com/Y6UR1I9.jpg

edit:

Quote:...I have selected 8bpc RGB, compression level 9 and hit Export

8 bits-per-channel = PNG24 not PNG8

There is a web export plugin for Gimp, very old but still works more-or-less. see: https://www.gimp-forum.net/Thread-advice...8#pid13718 download the zip. Unpack the zip. Put the webexport64.exe in your Gimp 2.10 user profile plug-ins folder
C:\Users\"yourname"\AppData\Roaming\GIMP\2.10\plug-ins

Find in the File menu -> Export for web . Looks like this: https://i.imgur.com/f9DIN0s.jpg

edit: If you need to process step-by-step
Scale the image. Do any other processing
Convert to indexed Image -> Mode -> Indexed
export the PNG (automatic pixel format)