ISO/IEC 15948:2004

Overview

ISO/IEC 15948:2004 specifies the Portable Network Graphics (PNG) datastream and associated file format for a lossless, portable, compressed computer graphics image intended for transmission across the Internet. The standard (ISO/IEC 15948:2004) defines the PNG functional specification and the Internet media type image/png. PNG supports indexed-colour, greyscale, and truecolour images with optional transparency, broad sample depth ranges, streaming and progressive display, and embedded colour-management data for accurate rendering across platforms.

Key Topics and Technical Requirements

• Lossless compression for individual images to preserve original pixel data.
• Supported image types: indexed-colour, greyscale, and truecolour.
• Transparency: optional alpha/transparency support for overlays and compositing.
• Sample depths: range from 1 to 16 bits per sample to accommodate low- and high-precision images.
• Streamability and progressive display: fully streamable datastream with an option for progressive rendering during transmission.
• Robustness and integrity: mechanisms for full file integrity checking and simple detection of common transmission errors.
• Colour management: ability to store gamma, chromaticity data and a full ICC colour profile for cross-platform colour matching.
• Media type registration: defines the Internet Media type image/png, facilitating consistent handling by web and network software.

Applications

ISO/IEC 15948:2004 (the PNG specification) is widely applicable where lossless, portable images are required:

• Web graphics (icons, logos, screenshots) that require sharp edges and transparency.
• User-interface assets and application graphics needing exact pixel fidelity.
• Image exchange between heterogeneous systems where consistent colour reproduction matters (uses embedded ICC profiles, gamma, chromaticity).
• Archival and documentation scenarios where integrity checking and lossless storage are important.
• Streaming or progressive delivery contexts (content delivery networks, web clients) that benefit from incremental display.

Who Uses This Standard

• Software developers and library authors implementing image encoders/decoders and viewers.
• Web and front-end developers choosing image formats for sites and apps.
• Browser and OS vendors ensuring consistent PNG rendering.
• Digital asset managers, archivists, and imaging professionals requiring lossless preservation and colour fidelity.
• Standards bodies and implementers registering or handling the image/png media type.

Related Standards

• The standard explicitly defines the image/png Internet Media Type used in web and networking contexts.
• PNG is commonly considered alongside other raster image standards (e.g., JPEG, GIF) when selecting image formats for quality, transparency, and compression trade-offs.

Keywords: ISO/IEC 15948:2004, PNG specification, Portable Network Graphics, image/png, lossless compression, ICC colour profile, transparency, progressive display.