PNG and JPG solve different problems
PNG (Portable Network Graphics) is a lossless format built for exactness — every pixel comes back out of a PNG file exactly as it went in, and it supports an alpha (transparency) channel, so parts of the image can be partially or fully see-through. This makes PNG the right choice for logos, icons, screenshots, and any graphic with sharp edges or text, where lossy compression would introduce visible artifacts. JPG (Joint Photographic Experts Group) is a lossy format built for photographic content — it compresses much more aggressively by discarding detail the human eye is less sensitive to, but it has no transparency support at all and handles sharp edges and flat colors relatively poorly, producing visible “ringing” artifacts around high-contrast boundaries like text.
Converting between them is common because many destinations — old upload forms, certain print workflows, email clients that mishandle PNG transparency, some ad networks — specifically require JPG regardless of what the source content actually is.
What happens to transparency during conversion
A PNG’s alpha channel stores, per pixel, how transparent that pixel is (from fully opaque to fully see-through). JPG has no equivalent channel, so converting necessarily requires deciding what color shows through where the PNG was transparent. This tool performs that step explicitly — compositing (blending) each pixel’s color with your chosen background color according to that pixel’s original alpha value — rather than silently defaulting to black, which is a common and jarring failure mode in less careful converters. Fully opaque pixels are unaffected; fully transparent pixels become exactly your chosen background color; partially transparent pixels (soft shadow edges, anti-aliased icon borders) are blended proportionally, so an edge that was 50% transparent ends up as a 50/50 mix of its original color and your background color, keeping edges looking smooth rather than developing a hard fringe.
Choosing the right background color
If you don’t know the destination background, white is the least risky choice because it matches the majority of documents, forms, and plain web backgrounds, and it avoids the harsh look of a black-filled transparent area (a very common default in naive converters, which happens when transparent pixels are treated as RGB value zero without considering alpha at all). If you know the specific background the image will sit against — a brand’s dark navy header, a specific gray card background in a design system — matching that color exactly makes the JPG version indistinguishable from a PNG with real transparency, since the eye can’t tell the difference between “actually transparent over this background” and “filled with the exact same color as this background.”
When PNG is still the better choice
Not every PNG should become a JPG. If the destination supports PNG and file size isn’t the deciding factor, keep flat-color graphics, logos, and text-heavy images as PNG (or WebP in lossless mode) — you’ll get a crisper result with no compression artifacts. Convert to JPG when: the destination explicitly requires it, the content is genuinely photographic (a photo that happens to be saved as PNG), or file size for photographic content matters more than the minor quality tradeoff of lossy compression. Checking the after-conversion file size this tool displays is a fast way to confirm you’re actually gaining something — if the JPG comes out larger than the PNG, the content probably wasn’t a good candidate for conversion in the first place.