What is PNG?
Portable Network Graphics is a raster format that uses lossless compression and supports alpha transparency. It represents palette, grayscale, RGB, or RGBA images but does not natively support CMYK output.
How PNG works
PNG organizes data as a signature followed by typed chunks, with critical chunks carrying image parameters, compressed pixels, and the end marker. Before compression, each scanline can be filtered against neighboring samples to make the byte stream more compressible; DEFLATE then encodes that stream without discarding pixel information. In an asset pipeline, ancillary chunks can preserve selected color and textual context, while decoders can safely ignore unknown ancillary extensions.
Key facts
- 1Every chunk carries a type, length, data, and integrity check. Unknown critical chunks must not be silently ignored, while unknown ancillary chunks need not block decoding.
- 2PNG filtering is reversible and is chosen per scanline before DEFLATE compression. It changes the compressibility of sample bytes, not the decoded pixel values.
- 3Transparency may be stored as a full alpha channel or, for suitable color types, in a transparency chunk. A palette entry can therefore have its own alpha value.
When PNG matters
Choose PNG for screenshots, sharp-edged graphics, or assets whose transparency and exact pixels must survive encoding. Photographs often produce larger files than with lossy formats, increasing storage and transfer costs.
Common use cases for file formats & compression
These examples cover file formats & compression broadly, not specifically PNG.
- Accepting heterogeneous uploads while producing a controlled set of delivery formats.
- Moving assets between cameras, editors, browsers, archives, and downstream APIs.
- Separating long-lived source files from compact derivatives optimized for a particular channel.
Working with file formats & compression
This guidance covers file formats & compression broadly, not just PNG.
A parser reads the file structure, identifies contained streams and metadata, and exposes them to a decoder or application. Conversion usually decodes the source representation and writes compatible information into a different structure or encoding.
This category covers file and bitstream formats, their structures, and the compression methods they use. A filename extension can be misleading, so evaluate the detected format, decoding support, metadata, transparency, color, timing, patents, and archival needs before choosing an output.
What you gain
- A suitable format preserves the properties a workflow actually needs.
- Standardized structures allow files to move between compatible tools and systems.
- Format conversion can improve delivery size, editability, or long-term accessibility.
What it costs
- Modern formats can save bandwidth but may need fallbacks for older clients and production tools.
- Converting to a simpler format can discard transparency, animation, metadata, color precision, or editability.
- Archival suitability, browser support, and editing support often favor different choices.
Before production
- 1Inspect the detected container, codec, MIME type, and magic bytes instead of trusting a suffix.
- 2Verify decoder support and preserve metadata, color, transparency, or timing when required.
- 3Retain the source when the chosen delivery format is lossy or tied to current software.