PNG to JPG - Convert PNG images to compact JPGs for easier sharing.

Understanding the JPG format

JPG (also written JPEG) is a lossy raster image format developed by the Joint Photographic Experts Group and standardized in 1992 as ISO/IEC 10918. It uses a discrete cosine transform (DCT) to convert 8x8 blocks of pixels into frequency coefficients, then quantizes those coefficients aggressively in higher frequency bands where the human visual system is least sensitive. The result is a substantial reduction in file size at the cost of some fidelity, with quality controlled by a quantization table typically expressed on a 0 to 100 scale.

Converting from PNG to JPG is a deliberate trade. PNG is a lossless format that preserves every pixel exactly as authored, including a full alpha channel for transparency. JPG discards both. Any transparent areas in the source PNG must be composited against a solid background color (typically white) before encoding, and any subtle gradients or sharp edges may show ringing or blocking artifacts after DCT quantization. In return, photographic content typically shrinks by a factor of five to twenty.

JPG remains the universal exchange format for photographs across browsers, email clients, content management systems, and cameras. It is the right destination when the source PNG is a photograph or screenshot of photographic material, when you need to upload to a platform that has size limits, or when transparency is not required. It is the wrong destination when the source contains crisp text, line art, UI elements, or any image that will be re-edited downstream.