PNG

PNG_transparency_demonstration_1

PNG-Gradient_hex

PNG-Gradient

PNG_color_depth_comparison

Pixel-prediction

Adam7_passes

Animated_PNG_example_bouncing_beach_ball

Portable Network Graphics (PNG) is a raster graphics file format that supports lossless data compression. PNG was created as an improved, non-patented replacement for GIF and is the most widely used lossless image compression format on the World Wide Web.

History

PNG was developed in 1995 by an Internet working group and was later specified in RFC 2083. The motivation for creating the PNG format was the need for a free and open image format that could replace GIF, which was encumbered by patents.

Features

PNG supports palette-based images (with palettes of 24-bit RGB or 32-bit RGBA colors), grayscale images (with or without alpha channel), and full-color non-palette-based RGB[A] images. PNG was designed for transferring images on the Internet, not for professional-quality print graphics, and therefore does not support non-RGB color spaces such as CMYK.

Compression

PNG uses a lossless data compression method known as deflate, which is the same algorithm used in the zlib compression library. This ensures that no image data is lost during compression, making PNG ideal for images that require high quality and precision.

Transparency

One of the key features of PNG is its support for transparency. PNG images can include an alpha channel, which allows for varying levels of transparency. This makes PNG a popular choice for web graphics, where images often need to blend seamlessly with different backgrounds.

Interlacing

PNG supports interlacing, which allows an image to be progressively displayed as it is downloaded. This feature is particularly useful for slow internet connections, as it provides a preview of the image before it is fully loaded.

Comparison with Other Formats

PNG is often compared to other image formats such as JPEG and GIF. Unlike JPEG, which uses lossy compression, PNG's lossless compression ensures that no image data is lost. However, PNG files are typically larger than JPEG files. Compared to GIF, PNG offers better compression and supports a wider range of colors and transparency options.

Usage

PNG is widely used on the web for images that require transparency or lossless compression. It is also commonly used for screenshots, as it can capture the exact appearance of the screen without any loss of quality.

Related Pages

• Graphics Interchange Format
• JPEG
• Raster graphics
• Alpha channel
• Deflate
• Zlib

See Also

• Image file formats
• Lossless compression
• Transparency (graphic)