PNG

A PNG is a way to save pictures.

It helps pictures look good on the web. It can even show clear parts.

This is great for you to see.

People made PNG to be a free tool. It was made to help move images on the internet. It can save many colors in one picture. It can also save a list of colors. This helps the file stay small.

Some PNGs can even move!

These are called APNG. Most web browsers can show them now. They are fun to watch!

A PNG is a way to save digital pictures.

It is a special format used on the internet. PNG stands for Portable Network Graphics. People made it to be a free tool. They wanted a better way to share images without paying fees.

One great thing about PNG is lossless compression. This means the file stays perfect when it is shrunk. It does not lose any detail or color. PNG can also show clear parts. This is called transparency. It lets you see through parts of an image.

PNG files are built using small parts called chunks. Some chunks are critical. These parts hold the main image data. Other chunks are extra. They might hold text or color info. This makes the format easy to grow and change.

Most PNGs are still images. But some can move! These are called APNG. They work like a small movie. Most web browsers can show them now.

They are fun to watch!

A PNG is a special way to save digital pictures on a computer.

It stands for Portable Network Graphics. This format is very important for the internet. It uses something called lossless compression. This means the file can get smaller without losing any detail. The image stays perfect every time you open it.

PNG files can also show transparency. This lets you see through clear parts of an image. This is very helpful when putting pictures on different backgrounds.

To work, a PNG file is built using small parts called chunks.

Each chunk carries a specific piece of information. Some chunks are critical, which means the computer must read them to see the image. The first critical chunk is called IHDR. It tells the computer the width and height of the picture. Another important chunk is called IDAT. This chunk holds the actual image data. There are also ancillary chunks. These are extra parts that hold things like text or color settings. A computer can safely ignore these if it does not understand them.

People created PNG because they wanted a free way to share images.

In late 1994, people learned they had to pay fees to use a different format called GIF. This caused many people to be upset. On January 4, 1995, a man named Thomas Boutell started a discussion to find a free alternative. Other experts joined in to help. A man named Oliver Fromme suggested the name PING. Eventually, the name became PNG, which is a recursive acronym. This means "PING Is Not GIF." The group that made it was called the PNG Development Group.

There are many important dates in the history of PNG. The full rules for the format were released in October 1996. In March 1997, it was published as a formal document called RFC 2083. The format was updated many times over the years. For example, version 1.1 came out in December 1998. Version 1.2 was released on August 11, 1999. Later, it became an official international standard in March 2004. Even today, the PNG Working Group continues to work on it. They released a new draft for a third edition on October 25, 2022.

You might already use PNG files without knowing it. Many web browsers use them to show pictures on websites. While standard PNGs are still images, there is a version that moves.

This is called APNG, or Animated Portable Network Graphics. It works like a small movie. Many browsers like Chrome and Edge can show these animations. Some systems, like the Sony PlayStation Portable, even use them for small pictures. PNG helps make the digital world look colorful and clear.

Portable Network Graphics, or PNG, is a raster-graphics file format designed for the internet.

It is a vital tool for digital imaging because it supports lossless data compression. Lossless compression means the file size is reduced without losing any original image detail. This ensures that the image remains perfect every time it is opened. PNG was specifically built to be a free, non-patented replacement for the Graphics Interchange Format (GIF). Unlike professional print formats, PNG does not support CMYK color spaces. Instead, it focuses on RGB and RGBA color models, which are ideal for web use.

The structure of a PNG file is built from an extensible series of parts called chunks. A PNG file begins with an eight-byte signature to identify the format. This signature includes specific values like 89 to detect certain transmission systems and the ASCII letters 'PNG' for easy identification. Following this header, the file contains various chunks that carry specific information. Each chunk consists of four parts: a length, a chunk type name, the actual chunk data, and a cyclic redundancy code (CRC). The CRC is a checksum used to ensure the data has not been corrupted.

Chunks are categorized as either critical or ancillary. Critical chunks are essential for the computer to read and render the image. If a program does not recognize a critical chunk, it must stop reading the file or warn the user. For example, the IHDR chunk must always be the first critical chunk. It contains the image's width, height, bit depth, and color type. The IDAT chunk is also critical because it holds the actual image data. Other critical chunks include PLTE, which holds a color palette, and IEND, which marks the very end of the image.

Ancillary chunks are optional parts that provide extra information. A computer can safely ignore these if it does not understand them. This design allows the PNG format to be extended with new features while staying compatible with older software. These extra chunks can store many types of metadata. For instance, the bKGD chunk defines a default background color. The gAMA chunk stores gamma values for color correction. Other chunks like tEXt or iTXt can store textual comments and descriptions. Some chunks, such as pHYs, can even hold information about the intended pixel size.

The history of PNG began with a legal dispute in late 1994. At that time, it was announced that using the GIF format would require paying royalties to Unisys. This was due to a patent on the Lempel–Ziv–Welch (LZW) compression algorithm. This news caused a massive outcry among computer users. On January 4, 1995, Thomas Boutell started a discussion on the Usenet group "comp.graphics" to plan a free alternative. Other experts joined the effort, eventually forming the PNG Development Group. Oliver Fromme suggested the name PING, which evolved into the recursive acronym PNG, meaning "PING Is Not GIF."

Since its inception, the PNG specification has undergone many revisions and standardizations. The full specification was approved by the World Wide Web Consortium (W3C) on October 1, 1996. It was published as RFC 2083 in March 1997. In 2004, it became an official International Standard known as ISO/IEC 15948. The format has continued to evolve through various versions. Version 1.1 was released in 1998 to fix color correction issues. Version 1.2 arrived in 1999 to add the iTXt chunk. Most recently, a new draft for a third edition was published in October 2022 to support high dynamic range (HDR) and Exif data.

While the standard PNG format is meant for single images, there have been efforts to add animation. In 2001, developers released the MNG format, but it did not gain much popularity. Later, in 2008, Mozilla developers introduced the Animated Portable Network Graphics (APNG) format.

APNG is now widely supported by major web browsers like Chrome and Edge. It is also used for thumbnails on systems like the Sony PlayStation Portable. Because APNG uses the same file structure as PNG, it demonstrates how the original chunk-based design allows for powerful new uses in the digital world.