When a PNG is required
Upload forms for logos and icons, app stores, some printers, presentation tools and photo editors often ask for PNG. If your picture is a .jpeg file — common from cameras, scanners and older phones — converting it gives you a file with the right format and ending.
What happens when you convert
The .jpeg picture is opened in your browser and saved as a lossless PNG with the same width, height and colours. Nothing is cropped or resized, and several files can be converted together.
What changes and what does not
The PNG is usually larger than the JPEG, because PNG keeps every pixel. Any blur, noise or compression marks already in the JPEG remain — converting cannot improve the picture. The background stays as it is; a JPEG has no transparency to keep.
Common problems and how to fix them
The form says the PNG is too big: PNG is not ideal for photos — ask if JPG is accepted, or compress with Compress Image using “Keep original format”. Colours look slightly different in another app: some apps handle colour profiles differently, but the pixels are unchanged. You need a transparent logo: the background must be removed in an image editor.
Good habits
Keep your original JPEG, use PNG for editing and graphics, and check the size limit of the place you upload to.