Why PNG transparency changes when you convert to JPG
Published and reviewed · Based on the current LocalShift implementation
JPEG does not store transparency. Converting a transparent PNG or WebP to JPG combines transparent and semitransparent pixels with a background color. In LocalShift, the default background is white.
Pick the background before converting
Open PNG to JPG, select your image, and choose a background color. White is useful for a white document page; another color may fit a particular design. The downloaded JPEG will include that color as part of its pixels.
The checkerboard behind a transparent sample on this site is a display aid, not part of the input image. The result preview shows the selected solid background. Download the sample files on the tool page to repeat the conversion yourself.
Inspect semitransparent edges
A shadow or antialiased edge can be partially transparent. Those pixels blend with the chosen background, so the edge can look different when flattened onto white rather than a dark color.
If the same logo must sit on several backgrounds, keeping transparency is usually more useful than making several JPEG copies. PNG and WebP can carry alpha information; the current PNG to WebP tool does not flatten it.
Quality does not mean transparency
Increasing JPEG quality cannot bring transparency back. It changes the lossy encoding setting, which can affect detail and file size. Inspect fine text, thin lines and logos at full size.
The converter retains image dimensions by default, with options to resize, rotate and flip. It does not crop, remove backgrounds or restore detail. Metadata and color profiles may change during browser re-encoding.
Use the result where it fits
Choose JPEG when the destination requires it or when you want an opaque image. Keep the original transparent source for later edits. Converting the JPEG back into PNG will not reconstruct the discarded transparency.
Browser encoders can produce different file sizes at the same quality setting. Our sample output documents one browser-generated result, not a promised file-size saving for every image.
References
General format references; LocalShift-specific behavior is documented and tested separately.