Why isn't my PNG converting to JPEG?

2 min read · Last updated June 2026

Even with Convert PNG to JPEG turned on, SlashImage only converts PNGs that are photographs with no transparency. Transparent images and flat-color graphics stay as PNG on purpose - PNG is the better format for them, and converting would make the file larger. SlashImage detects this automatically and picks whichever format gives the smaller file.

Symptom

You turned on Convert PNG to JPEG, but a PNG in your Media Library is still a PNG. A converted image shows a PNG → JPEG conversion line in its Media Library details, and you are not seeing it for this image.

Cause

SlashImage converts a PNG to JPEG only when all of the following are true. If any one is not met, the image correctly stays a PNG.

  • The setting is on. Convert PNG to JPEG is under Output Formats at Media > SlashImage, and is off until you opt in. Its help text reads "When the PNG has no transparency. Saves extra space."
  • The PNG has no transparency. JPEG cannot store transparency, so any PNG with see-through areas is kept as a PNG. This protects logos, icons, and graphics with transparent backgrounds.
  • The image is a photograph. Conversion is limited to photographic content. Flat-color graphics, illustrations, charts, and other low-color or vector-style PNGs stay as PNG, because PNG compresses those better and JPEG would add blur.
  • JPEG actually comes out smaller. SlashImage compresses the image both ways and keeps whichever is smaller. If the JPEG would not beat the optimized PNG, it keeps the PNG, and a tie stays PNG.
  • You are not using lossless mode. In lossless mode the PNG is kept as-is and never converted.

Resolution

  1. Confirm the setting is on: go to Media > SlashImage, scroll to Output Formats, and check that Convert PNG to JPEG is toggled on.
  2. Look at the image. If it has transparency, or it is a logo, icon, illustration, or flat-color graphic, it is meant to stay a PNG. There is nothing to fix.
  3. If it is a true photograph with no transparency and still is not converting, make sure your compression mode is not set to lossless, then re-optimize the image. See How do I re-optimize an image?.

Your WebP and AVIF versions are generated either way, so delivery is unaffected by whether the original stays a PNG or becomes a JPEG.

See also

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