PNG to JPG

JPEG has no alpha channel. It cannot store transparency in any form. So when a transparent PNG becomes a JPEG, every transparent pixel has to become some actual color.

Most tools fill them with black without mentioning it, which is why logos exported to JPEG so often arrive inside an unwanted dark box. This page fills them with white by default and gives you a switch to control it, because the choice belongs to you rather than to an encoder's default.

If the transparency matters, do not convert to JPEG at all. Keep the PNG, or use WebP, which is smaller than PNG and keeps the alpha channel intact.

Converting PNG to JPEG is worth it when the content is photographic. A photograph stored as PNG is commonly five to ten times larger than the same image as a quality-82 JPEG, for no visible benefit whatsoever — PNG simply has no way to exploit the noise and gradient that make up a photograph.

It is the wrong move for screenshots, logos, diagrams and anything containing text. Those have hard edges, and lossy encoding puts visible haloes around them. Chroma subsampling makes colored text worse still. For that content the PNG is usually smaller as well as sharper.

JPEG has no alpha channel and cannot store transparency. Converting a transparent PNG forces those pixels to become something, and most tools fill them with black — which is why a logo exported to JPEG arrives in an unwanted dark box. Keep it as PNG, use WebP (alpha support, typically 25–35% smaller than PNG), or flatten onto a chosen background deliberately.

Color is the other gap. Screens mix additively in RGB; printing presses mix subtractively in CMYK, and converting between them always approximates. A CMYK JPEG is converted to RGB before a browser can display it, and saturated cyans and deep blues can shift noticeably. Compress and resize in RGB for screens, and keep a separate CMYK master for print.

Lossless compression rewrites the file so every pixel survives exactly — decode it and you get the original back, byte for byte. PNG, GIF, lossless WebP and ZIP all work this way.

Lossy compression discards detail on purpose. JPEG converts the image to a frequency representation and throws away the high-frequency detail your eye is least likely to miss. That is irreversible, and it is how lossy reaches sizes lossless cannot: a photograph saved as PNG is routinely five to ten times larger than the same photograph as JPEG.

Neither is better. Photographs suit lossy encoding; screenshots, logos and line art suit lossless, because lossy encoders leave haloes around hard edges.