What is .PNG File Extension?

A PNG file is a transparent background image saved in the Portable Network Graphic (PNG) format, which is often used to save web graphics, digital pictures, and other images with transparent backgrounds. It’s a raster graphic that’s comparable to a.JPG picture but with lossless compression and transparency capabilities.

PNG transparency demonstration – Image courtesy – wikipedia.org

More Information

Along with JPEG, GIF, TIFF, and EPS, PNG is one of the most common image formats. You could come across a PNG file in the following situations:

Downloading a picture from the internet or attaching an image to an email
Using an image editor to save a digital photograph, such as a logo or symbol created by a graphic designer or web designer.
Using Windows or macOS 10.4 and later to take a screenshot (Ubuntu Linux also stores print screen screenshots in the PNG format)

Why was the PNG format created?

PNG was designed in 1995 as a free alternative to GIF for exchanging pictures over the internet. It improved on the GIF format’s limitations, which included a patent license and only allowed a restricted amount of colors. Furthermore, unlike GIF pictures may only have entirely opaque or fully transparent pixels, PNG images can have an 8-bit transparency channel, allowing the image colors to transition from opaque to transparent.

Support for indexed (palette-based) 24-bit RGB or 32-bit RGBA (RGB + a fourth alpha channel) color pictures is another PNG feature. Full-color, non-indexed RGB or RGBA photos, as well as grayscale images, are supported by the format.

While the PNG format has grown in popularity, it is a single-image format, whereas GIF can store numerous pictures. The GIF format allowed users to preserve basic animations as GIF files, which led to a rebirth of the format online, particularly on social media. The PNG Development Group established the Multiple-image Network Graphics (.MNG) format in 2001 to address this problem, although it was not as extensively embraced as the GIF format.

How to Open a PNG File?

Many free and commercial tools, including most image editors, video editors, and web browsers, can open PNG files. Microsoft Photos and Apple Preview, which are included with Windows and macOS, both support PNG images.

Image Transparency

PNG has a wide range of transparency choices. A single pixel value can be designated transparent in true-color and grayscale pictures, or an alpha channel can be added (enabling any percentage of partial transparency to be used). Alpha values can be applied to palette entries for paletted pictures. If the number of such values recorded is fewer than the total number of palette entries, the remaining entries will be entirely opaque.

To avoid pixels being unintentionally transparent, the scanning of pixel values for binary transparency should be done before any color reduction. This is most likely to be a problem for systems that can decode pictures at 16 bits per channel (as required by the standard) but only output at 8 bits per channel (the norm for all but the highest end systems).

PNG standardized on “unassociated” (“non-premultiplied”) alpha storage, which implies that imagery is not alpha encoded; the emissions represented in RGB are not the emissions at the pixel level. This implies that the over operation will multiply RGB emissions by alpha, making it impossible to accurately depict emission and occlusion.

Interlacing

The Adam7 technique is a 2-dimensional, 7-pass interlacing mechanism available in PNG. This is more advanced than GIF’s 1-dimensional, 4-pass method, and enables for a crisper low-resolution image to be shown early in the transmission, especially if bicubic interpolation algorithms are utilized.

The 7-pass technique, on the other hand, tends to impair data compressibility more than simpler designs.

Animation

Animation is indeed not possible with PNG. MNG is a PNG extension that accomplishes this, and it was created by members of the PNG Group. MNG is similar to PNG in terms of fundamental structure and chunks, but it is substantially more sophisticated and has a distinct file signature, making it incompatible with ordinary PNG decoders. As a result, most web browsers and programs have withdrawn support for MNG.

The Mozilla Foundation’s engineers proposed APNG as a solution to MNG’s complexity. It’s based on PNG, allows for animation, and is less complicated than MNG. For PNG decoders that do not support APNG, APNG provides a fallback to single-image display. All of the main online browsers now support the APNG file format. Since the engine was updated to Blink, APNG is supported in Firefox 3.0 and higher, Pale Moon (all versions), and the newest version of Opera. Safari 8 for iOS 8 and Safari 8 for OS X Yosemite both utilize the WebKit engine, which supports APNG. Google Chrome 59.0 was the first to introduce APNG support, and it was quickly followed by Chromium 59.0. The new Chromium-based engine in Microsoft Edge now supports APNG.

In April 2007, the PNG Group opted not to accept APNG. ANG, aNIM/mPNG, “PNG in GIF” and its subclass “RGBA in GIF” were all discussed as alternatives. Only APNG, however, is now supported by all major web browsers.