Using GIMP 2.8.22 on Windows. When I export images, gimp usually makes
PNG the default. How do I make
JPG the default format when exporting?
There's finally a real setting for this, as of GIMP 2.10 (and possibly earlier), you can simply go to Edit > Preferences >Image Import and Export, and change the export file type as you please.
In addition, the above exe editing technique doesn't work anymore, since they changed how it's handled to implement this.
Just type the new filename, and add the .jpg extension directly after the file name. GIMP will automatically change the file type to jpeg. See screenshot below.
When you do this there is no need to select .jpg in the Select File Type drop down.
Next time you use Export As, GIMP should remember your choice and append the .jpg extension.
If you quit GIMP and restart the application, GIMP goes back to png as default. I found this post which suggests one method of changing this behaviour - but I can't vouch for it, since I've never tried it. Whether or not it still works on recent versions, I have no idea. The post is old.
Here's the quote should the link above ever fail
The only way I found to set this default extension to .jpg without recompiling Gimp is: - Edit the Gimp executable (/usr/bin/gimp-2 on Linux, \bin\gimp-2.8.exe on Windows) with an hexadecimal editor. You can use ghex (1) on Linux. Search for the string ".png". There are few occurrences of it. The right one is there: file:///we/only/care/about/extension.png- Overwrite png with jpg, that is, write 'jp' over 'pn', save the file and you are done. You'll be prompted for a .jpg file by default. See screenshot below.
Source: GIMP Users group on Flickr (user Francois Collard)