Does converting a JPG to PNG improve quality?

PNG is “lossless” and JPG is “lossy”, so it seems natural that converting a JPG to PNG would make it better. It does not. It keeps the image exactly as it is, including every flaw the JPG compression already introduced, and usually makes the file much larger.

What lossless really means

Lossless means that saving as PNG does not lose anything further. It does not mean PNG can restore what was lost earlier. When a photo was first saved as JPG, some fine detail was thrown away and small artefacts appeared: blocky patches in smooth areas, faint halos around sharp edges. Converting to PNG records those pixels faithfully. The artefacts are preserved, not repaired.

What happens to the file size

JPG is designed for photographs and compresses them very efficiently. PNG is designed for graphics with flat colours and compresses photos poorly. A photo converted from JPG to PNG is often several times larger, with no visible difference. That is the opposite of what most people want.

When converting to PNG does make sense

• You are going to edit the image repeatedly. Every time a JPG is opened, edited and saved as JPG again, it loses a little more. Converting once to PNG with JPG to PNG and editing the PNG stops that further loss. Make the final JPG at the end.
• A form or program only accepts PNG. Then convert, and accept the larger file.
• You need transparency later. JPG cannot store a transparent background. PNG can, although converting does not create the transparency by itself; you still have to remove the background in an editor.
• Graphics that were wrongly saved as JPG. A logo or screenshot saved as JPG has fuzzy edges. Converting will not sharpen them, but it stops them getting worse in future edits.

How to actually get better quality

• Find the original. The camera file, the original export from the designer, or the full-resolution photo from the sender.
• Save JPGs at higher quality next time. In Compress Image, quality in the 80s is visually close to the original for most photos; the low 60s and below show artefacts.
• For graphics, start in PNG or SVG and only make a JPG if a photo-like file is required.

The same goes for other conversions

Converting a small image to a larger size does not add detail, and converting a WebP or AVIF to JPG does not improve it either. Conversions change the container, not the content. Use them for compatibility, which is what the Image Converter is for: getting a file into the format a program or website accepts.

For choosing formats from the start, see JPG vs PNG vs WebP. For the opposite conversion, and what happens to transparency, see PNG to JPG and transparency.