When to convert PNG to JPG
- An upload form only accepts JPG
- You want to email a lot of screenshots
- A photo was saved as PNG and the file is huge
About transparency
JPG cannot be transparent, so any see-through parts of your PNG are filled with a solid colour. White is used by default and you can choose any other colour above.
Questions
How much smaller will the file be?
For photos, often 3 to 10 times smaller. For simple graphics with flat colours the saving is less.