What is portable network graphics image

PNG (Portable Network Graphics) Home Site

Welcome to the PNG Home Site, maintained by Greg Roelofs. Our hero likes to speak of himself in the third person, but don't let that put you off; this is intended to be a mostly serious set of reference pages for locating information, applications and programming code related to the 28-year-old PNG image format.

Canonical URL: http://www.libpng.org/pub/png/ (California, USA)

Note that the PNG home site has moved four times since 1995 (though the URL has changed only three times, and hopefully never again). The current site is hosted by the excellent folks at SourceForge.  

The PNG web site is organized into four basic categories of information (blue and white headings below), not counting the separate MNG site (covering PNG's animated and lossy cousins). A complete site map to the 110+ pages is available, but the basics are summarized here.

The informal history below is worth reading both for general background and for a summary of PNG's main features, but most non-programmers will probably find the basic introduction, the FAQ, and perhaps the longer history to be of the greatest interest and utility. The PNG-supporting application lists, on the other hand, are no longer particularly important (or maintained), insofar as virtually every image-related application has supported PNG natively--and well--for more than a decade. They too are now historical in nature.

A Basic Introduction to PNG Features (recommended for new visitors)

Current Status of PNG (recommended for new visitors)

Frequently Asked Questions (recommended for new visitors)

An Informal History of PNG (and a More Detailed History)

News of the PNG Development Group

Links to Other PNG Resources (includes mailing lists)

PNG Technical Documentation

• PNG Specification and Extensions (latest version)
• zlib Technical Documentation
• MNG / JNG Technical Documentation

PNG: The Definitive Guide and Related Books

Applications with PNG Support

• Browsers
• Image Viewers
• Image Editors
• Image Converters
• 3D Applications (also VRML Browsers)
• Games / Entertainment
• Office / Business Applications
• Scientific / Graphing Applications
• Miscellaneous Applications

Hardware with PNG Support

PNG Programming Information:

• PNG-supporting Libraries and Toolkits
  • libpng home page
  • zlib home page
  • libmng home page
• PNG Source Code

PNG Images:

• Willem van Schaik's Test Suite of PNG Icons
• Greg's Test Suite of PNG Textures for VRML
• Ray-traced PNG Interlacing Demo (also JPEG version)
• Miscellaneous Transparent PNGs using IMG Tags (includes links to screenshots)
• Miscellaneous Transparent PNGs using OBJECT Tags (also strict HTML 4. 0 version)
• Miscellaneous 32-bit RGBA PNGs
• Photographic PNGs with Alpha Transparency:
  • Icicles
  • Redbrush flower (Ohia Lehua)
  • Magnolia tree
  • Horned Owl
• Browser Gamma-Correction Test
• Browser Color-Correction Test

Links to Other PNG Resources (includes pointers to more PNG images)

Multiple-image Network Graphics (MNG) Home Site
(includes JNG: JPEG with alpha-transparency)

What It Be (An Informal History)

So what is PNG, and why is it worthy of its own home site? PNG (pronounced "ping") is the Portable Network Graphics format, a format for storing bitmapped (raster) images on computers. Unofficially its acronym stands for "PNG's Not GIF." PNG was designed to be the successor to the once-popular GIF format, which became decidedly less popular right around New Year's Day 1995 when Unisys and CompuServe suddenly announced that programs implementing GIF would require royalties, because of Unisys' patent on the LZW compression method used in GIF. Since GIF had been showing its age in a number of ways even prior to that, the announcement only catalyzed the development of a new and much-improved replacement format. PNG is the result.

(By the way, despite the implications in some of CompuServe's old press releases and in occasional trade-press articles, PNG's development was not instigated by either CompuServe or the World Wide Web Consortium, nor was it led by them. Individuals from both organizations contributed to the effort, but the PNG development group exists as a separate, Internet-based entity.)

That's only half the story, however; PNG would deserve a home page even if all that had not taken place, just because it's so darned nifty. Yes, it's not every day you come across an image format and say, "Outraaageous!" In fact, you may never say that in your entire lifetime (truly a pity), but PNG is still cool. Some of its spiffier features include:

• unambiguous pronunciation (ooo, baby!)
• multiple CRCs so that file integrity can be checked without viewing
• ultra-clever magic signature that can detect the most common types of file corruption
• better compression than GIF, typically 5% to 25% (but often 40% or 50% better on tiny images)
• non-patented (you betcha!), completely lossless compression
• majorly gnarly two-dimensional interlacing scheme
• 1-, 2-, 4- and 8-bit palette support (like GIF)
• 1-, 2-, 4-, 8- and 16-bit grayscale support
• 8- and 16-bit-per-sample (that is, 24- and 48-bit) truecolor support
• full alpha transparency in 8- and 16-bit modes, not just simple on-off transparency like GIF
• "palette-alpha" mode, effectively transforming normal RGB palette into RGBA
• gamma correction for cross-platform "brightness" control
• color correction for cross-platform, precision color
• both compressed and uncompressed text chunks for copyright and other info
• full Year 2000 (Y2K) support, and then some (good for at least 63 millenia! yowza!)
• free and complete reference implementation with full source code

Not exactly spiffy, but worth mentioning anyway:

• officially registered Internet media ("MIME") type: image/png

PNG also supports things like suggested quantization, "smart" extensibility, a standard color space and lots of other excellent stuff, but let us leave all that aside for now. Those who want a quick explanation of the main features can check out Greg's Basic Introduction to PNG Features. Those who want all of the gory details can either find a library with the July 1995 issue of Dr. Dobb's Journal and read Lee Crocker's PNG article; read a copy of Greg's O'Reilly book, PNG: The Definitive Guide; or else go read the full Portable Network Graphics Specification, a reasonably concise W3C Recommendation (the very first one!) that is amazingly well written and understandable. (Greg had no part in the actual writing of it, so he can say things like that.) See the PNG documentation page for links to plain ASCII, PostScript (US letter-size) and PDF versions, and see the W3C's PNG page and official press release for links to related documentation on gamma and color correction.

Note that the PNG specification was updated to version 1.1 on New Year's Eve 1998 (that is, 31 December 1998). It included new chunks for cross-platform color correction (sRGB and iCCP), a revised and much more sensible description of gamma correction, and a number of other minor improvements and clarifications (all fully backward compatible, of course!). A second, more minor update (version 1.2) was released in August 1999; its only change was the addition of the iTXt chunk (international text).

In addition, PNG began the long process of international standardization^* in 1999 (see the 10 May 1999 news item for details), thanks largely to its inclusion in VRML97. It finally completed that process and became the joint ISO/IEC standard 15948:2004 nearly five years later (see the 3 March 2004 news item), a few months after it was also rereleased by the W3C (with identical content) as their "PNG Second Edition" Recommendation.

^*PNG was already part of the UK profile for MHEG-5 on digital terrestrial television; MHEG-5 is the international standard for a next-generation teletext system that shares a number of features with HTML. PNG is also used in MHP, the Java-based Multimedia Home Platform for digital video systems, and was included in HAVi, the somewhat defunct Home Audio-Video Interoperability standard for 1394-based home networking.

And the design of the multi-image extension to PNG known as MNG is officially complete (version 1.0 of the MNG specification was released on 31 January 2001), with quite a number of applications available and a free reference library, too.

By now you're undoubtedly drooling over such an incredibly well-designed image format and wondering where you can find applications or programming tools that support it. Well, wonder no further! Greg aims to please.

Last modified 5 December 2022, you betcha.
Copyright © 1995-2022 Greg Roelofs (contact).       png-printable.html

TIFF file format in detail : Document scanners

TIFF (English Tagged Image File Format) is a format for storing raster graphic images. TIFF has become a popular format for storing high-color images. It is used in scanning, faxing, OCR, printing, and is widely supported by graphics applications. TIFF was chosen as the main graphic format of the NeXTSTEP operating system and from there support for this format was transferred to Mac OS X. The format was developed by Aldus Corporation in collaboration with Microsoft for use with PostScript. The specification's owner, Aldus Corporation, subsequently merged with Adobe Systems, which currently owns the copyright to the specifications.

TIFF files usually have a .tiff or .tif extension.

TIFF Compression

The TIFF format is more commonly used in the printing industry. This is the most popular raster format for printing. There is an opinion that TIFF is not subject to compression, since the file size of this format is usually very high. However, this is an erroneous opinion.

When saving a file in TIFF format, the application gives you the choice of whether to use compression or not, and what type of compression to use. Using compression significantly reduces the file size. However, compression may or may not result in loss of image quality, depending on the choice of compression type.

Let's take a closer look at compression algorithms,

There are three TIFF compression algorithms: LZW , ZIP and JPG . In printing houses, the first two are most often used, since the latter involves compression with loss of quality.

LZW aka Lemple-Zif-Welch was developed back in 1977 by two Israeli mathematicians, whose names are Lempel and Ziv. An improved version was published in 1984. LZW is considered the most "painless" data compression algorithm, since compression is carried out without distortion. The LZW algorithm is quite simple: it searches and replaces the same data. Character strings are replaced with encoded information. These codes can be absolutely any length, only one condition must be met: these codes must contain more bits than are contained in a single character. The best result is achieved when raster files with large areas of uniform fills are compressed. In printing houses, this algorithm is considered the best, as it is able to give high-quality compression in the absence of distortion in the file.

Prepress specialists use the LZW compression algorithm not only when working with a TIFF file. LZW is also effective at compressing PDF and PostScript files.

The compression algorithm ZIP is similar to that used in PKZip. This compression method is also harmless to the original file, that is, it does not give any distortion. In addition to TIFF, the scope also covers PDF and PostScript formats.

Compression algorithm JPEG is a simple encapsulation of the JPEG format into the TIFF format. This algorithm assumes a compression with loss of quality.

Loss of quality depends on the compression ratio set. Not all user applications allow the user to select this value. However, the TIFF format allows you to store images compressed according to the JPEG standard without data loss (JPEG-LS).

The JPEG-LS format was originally developed for storing images for medical purposes, that is, for those cases where it is important to have a large image without the slightest quality loss. As already mentioned, the LOCO-I format developed within the walls of HP Labs was taken as the basis. Then it was finalized by the joint efforts of Hewlett-Packard and Mitsubishi. Both companies have allowed their patents on this format to be used without paying a license, so JPEG-LS can be found in regular PC programs as well.

However, we recommend that you use the LZW compression algorithm in all cases when saving files in the TIFF format, as this option ensures that there is no loss in image quality and at the same time provides the maximum reduction in file size.

Complete network and network interface scanners. Features and Differences :

The Network Scanner is a stand-alone, self-sufficient device that connects to an enterprise's LAN (wired or/and wirelessly, depending on the specific model) and is able to perform its network functions completely on its own without additional network agents.

In simple terms, the network document scanner is an in-line scanner integrated with a computer in a single housing. Such a scanner has an operating system (Windows or Linux, and some of the latest models even Android). Such a network scanner can be authorized in a Windows Active Directory domain, have its own account for interacting with a network server, receive an address book via LDAP to register scan operators, and much more. The network scanner is able to independently send scanned documents to a specified email address, a specified network folder, or an FTP server. Let's call this set of functions - network sending.

Due to the fact that the network scanner is a stand-alone device, all functions for generating, processing images and generating files for subsequent sending are performed inside the scanner. Image processing means not only its digitization by a scanning matrix, but also the inclusion of image enhancement functions: adjusting brightness and contrast, removing noise, rotating and de-skewing, subtracting background color, image optimization algorithms when converting to grayscale and black and white format, and much more. other. In addition, the scanner can implement such functionality as full-text text recognition on a document and saving the text layer (OCR).

Of course, the implementation of the above functionality imposes serious requirements on the hardware of the network scanner: the built-in computer unit must have quite powerful characteristics so that the activation of all the listed functions does not lead to a critical slowdown in the scanning process.

Now that we have an understanding of what a full-fledged network scanner is, let's take a closer look at the "network interface scanners" group, which we cannot call full-fledged network scanners for certain reasons. Let's call these scanners conditionally - pseudo-network .

Fundamental difference: this group of scanners does not perform network sending on its own. The scanner requires a host computer with a scanning program and a scanner driver. Formally, the network interface of this type of scanner is used to replace a local connection to a computer via USB with an Ethernet connection. This type of scanner connection allows several users to work together with the scanner, which is a very popular task in everyday office work. In this collaboration, the operator selects a job on the scanner and starts scanning. The scan result is transferred and processed on his computer in accordance with the settings of the job profile. Image processing, in this case, takes place on the computer, as well as OCR and other functions. The exception is some scanner models in which image processing is implemented at the hardware level.

We should also consider scanners with wireless Wi-Fi interface. If the scanner is connected via Wi-FI in infrastructure mode through a router, this is a simple replacement of a wired network connection with a wireless one. There are no functional differences.

However, many document scanners with Wi-Fi can work in Ad-Hoc mode, which allows you to transfer the image from the scanner directly to another wireless device (tablet or phone). In this sense, this scanner can also be called an autonomous and self-sufficient network device.

Separately, it should be noted the function of saving image files to a directly connected USB flash drive. This function can be implemented both in network and pseudo-network scanners. One manufacturer actively using this feature is Brother.

It should also be noted that almost any local (non-network) document scanner can be turned into a pseudo-network scanner.

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