Portable Network Graphics

What is a PNG file?

A PNG (Portable Network Graphics) file is a raster graphics file format that supports lossless data compression. PNG was developed as an improved, non-patented replacement for Graphics Interchange Format (GIF). PNG supports palette-based images, grayscale images, and full-color non-palette-based RGB/RGBA images with transparency support.

More Information

PNG was created in 1995 by a group of graphic software developers led by Thomas Boutell in response to patent issues with the GIF format. The PNG Development Group released the first version of the PNG specification in 1996, and it became an official ISO/IEC standard in 2004.

PNG quickly gained popularity on the web due to its superior compression, transparency support, and lack of patent restrictions. Today, PNG is one of the most widely used image formats on the internet, particularly for images that require transparency or high quality with sharp edges, such as logos, icons, and screenshots.

PNG Format

PNG uses a lossless compression algorithm based on the DEFLATE specification, which is also used in ZIP files. The format supports several color types and bit depths:

Color Types

• Grayscale - Black and white images
• Grayscale with alpha - Black and white with transparency
• Palette - Up to 256 indexed colors
• RGB - True color (16.7 million colors)
• RGBA - True color with alpha transparency

Bit Depths

• 1-bit - Black and white (palette or grayscale)
• 2-bit - 4 colors/shades (palette or grayscale)
• 4-bit - 16 colors/shades (palette or grayscale)
• 8-bit - 256 colors/shades (palette or grayscale)
• 16-bit - High color depth (grayscale or RGB)

Key Features

• Lossless compression - No quality degradation
• Alpha transparency - Variable opacity levels
• Gamma correction - Consistent color across devices
• Metadata support - Text chunks for image information
• Progressive display - Interlaced rendering option

How to open a PNG file

PNG files are widely supported and can be opened with virtually any image viewer or web browser:

Built-in Applications

• Windows Photos (Windows) - Default image viewer
• Preview (Mac) - Default image viewer for macOS
• Image Viewer (Linux) - Various default viewers
• Web browsers - All modern browsers support PNG

Image Editing Software

• Adobe Photoshop - Professional image editing
• GIMP - Free open-source image editor
• Adobe Illustrator - Vector graphics (can import PNG)
• Canva - Online design tool
• Paint.NET - Free Windows image editor
• Pixelmator - Mac image editor

Online Viewers

• Google Photos - Cloud-based photo viewing
• Dropbox - Can preview PNG files
• OneDrive - Microsoft's cloud storage viewer

How to edit a PNG file

PNG files can be edited with various image editing applications:

Professional Tools

• Adobe Photoshop - Industry standard for photo editing
• Adobe Illustrator - Vector graphics with PNG import/export
• Sketch (Mac) - UI/UX design tool
• Figma - Web-based design tool

Free Alternatives

• GIMP - Full-featured free image editor
• Paint.NET - Windows-only free editor
• Canva - Online design tool with free tier
• Pixlr - Web-based image editor

Simple Editing

• MS Paint - Basic editing on Windows
• Preview (Mac) - Simple annotations and cropping
• Online editors - Photopea, Canva, Pixlr

How to create and convert PNG files

Creating PNG Files

• Screen capture - Most screenshot tools save as PNG
• Digital cameras - Some cameras can save in PNG format
• Graphic design software - Export designs as PNG
• Online tools - Create graphics and export as PNG

Converting to PNG

Most image editing software can convert from other formats:

From JPEG: Use image editors to convert with quality preservation From GIF: Convert to maintain or improve quality From BMP: Reduce file size while maintaining quality From TIFF: Convert for web use From SVG: Rasterize vector graphics to PNG

Online Conversion Tools

• CloudConvert - Supports many formats
• Online-Convert - Free image conversion
• Convertio - Web-based converter
• TinyPNG - Compression and conversion

Technical Specifications

• File Extension: .png
• MIME Type: image/png
• Developed by: PNG Development Group
• Released: 1996
• Standard: ISO/IEC 15948:2004
• Compression: Lossless (DEFLATE algorithm)
• Maximum dimensions: 2,147,483,647 × 2,147,483,647 pixels

Common Use Cases

• Web graphics - Logos, icons, buttons
• Screenshots - Software documentation
• Digital art - Illustrations with sharp edges
• Transparent images - Overlays and cutouts
• UI elements - Interface components
• Print graphics - High-quality printing
• Social media - Profile pictures and graphics
• E-commerce - Product images with transparency

Advantages

• Lossless compression - No quality degradation
• Transparency support - Alpha channel transparency
• Wide compatibility - Supported everywhere
• No patent issues - Free to use and implement
• Metadata support - Can store image information
• Progressive display - Can load incrementally
• Color accuracy - Excellent color reproduction
• Sharp edges - Perfect for text and line art

Limitations

• File size - Larger than JPEG for photographs
• No animation - Static images only (use APNG for animation)
• Limited HDR support - Better options available for high dynamic range
• Browser compatibility - Some very old browsers lack full support
• Memory usage - Can use significant RAM for large images

PNG vs Other Formats

PNG vs JPEG

• PNG: Lossless, transparency, larger files
• JPEG: Lossy, smaller files, no transparency, better for photos

PNG vs GIF

• PNG: Better compression, more colors, better transparency
• GIF: Animation support, wider legacy support

PNG vs WebP

• PNG: Wider support, larger files
• WebP: Better compression, newer format, limited support

PNG vs SVG

• PNG: Raster format, pixel-based
• SVG: Vector format, scalable, smaller for simple graphics

Optimization Tips

• Use appropriate bit depth - Don't use 24-bit for simple graphics
• Optimize palette - Reduce colors when possible
• Compress further - Use tools like TinyPNG or OptiPNG
• Consider alternatives - Use JPEG for photos, SVG for simple graphics
• Remove metadata - Strip unnecessary information to reduce size