PNGJPG

PNGJPG is a non-standard, informal term used to describe a hypothetical image format that attempts to combine features of the Portable Network Graphics (PNG) and JPEG formats. It does not refer to an official specification and has no universal definition. In practical discussions, PNGJPG typically denotes one of two ideas: a dual-stream container that stores both a lossless PNG image and a lossy JPEG version within a single file, or a single image file that can be decoded as either PNG or JPEG by specialized software.

Variants and implementations vary. Some proposals describe a file wrapper that embeds a PNG data stream alongside a JPEG data stream, with an index or metadata indicating which image to display. Other interpretations imagine a single file that contains both streams in separate sections, with a consumer selecting the preferred representation at display time. Because neither PNGJPG nor its variants are officially standardized, interoperability relies on custom tooling.

Technical considerations include handling of color spaces, gamma, transparency (alpha channel), and metadata. PNG supports lossless compression and full alpha transparency; JPEG provides efficient lossy compression but does not support alpha. Merging or multiplexing these properties requires clear rules for color management and for how decoders should fail gracefully if the chosen representation is unavailable. Real-world support is therefore limited to experimental projects and academic exercises.

Use cases discussed in informal discussions include archival workflows that preserve a lossless master alongside a smaller lossy preview, and testing of dual-representation decoders. However, due to lack of standardization and broad software support, PNGJPG remains a niche concept rather than a practical replacement for established formats such as PNG, JPEG, WebP, or HEIF.