Understanding Web Graphic Formats

Understanding Web Graphic Formats

The evolution of web graphics formats from GIF and JPG to the new W3C endorsed PNG format.

Before web page publishing in the 1990s, the introduction of small computers to homes and businesses in the 1980s initiated up the world to desktop publishing. This new breed of publishers used primitive computers and software, by today’s standards, to create newsletters and flyers that before that time was created using typesetting equipment available at traditional paper printers.

With desktop publishing and paper printing, the publisher controlled the final output, as the finished product was a piece of paper handed to someone. Print graphics were usually based on the quality of the image. The publisher used a graphic that looked good on a standard piece of paper, typically 8 1/2 by 11 inches in size.

As the world of web page publishing came to life in the 1990s, there was a new set of challenges for this new breed of publishers. When you create something on paper, you know how others will see it. Still, when you make something for the web, you are never sure what others will see because different browsers show colors. Differently, different screens have different resolutions and color depths. A new concept introduced with web graphics was the concept of images not measured in inches but pixels.

Understanding Pixels

Early computer monitors were cathode ray tube (CRT) technology, monitors. Different flags for each of the three colors, red, green, blue, were created by a vacuum tube with three electron guns, one for the color red, green, and blue. 

Graphics on a vacuum tube monitor are made up of individual dots of color known as pixels, short for picture element. 

Image resolution is an important concept to consider in designing web graphics for a straightforward reason; regardless of how well you create a graphic, in the end, the user’s monitor determines the final output of the image. The feature of a display depends on its presentation, how many pixels it can perform, and how many bits describe each pixel.

Large and bulky CRT technology was once the only type of computer monitor in use. While CRT monitors are now rare, the current LCD (liquid crystal display) still uses the concept of the pixel.

What is a bitmap?

Generically the term bitmap is used to describe a type of file created by a map of dots used as a graphic on a website. Bitmap graphics are sometimes referred to as raster graphics.

There is often uncertainty because the regular bit-mapped graphics format applied in the Windows context uses the file extension BMP, model, filename.bmp. The Windows environment BMP tends to store graphical data inefficiently because there is no compression, and files are more significant than similar files in other bitmap formats.

GIF first widely supported web graphic format

The GIF, the graphics interchange format, was developed in 1987 by CompuServe Information Service, one of the leading online services, as a free and open specification. In the early days of online services, there was a need for a standard file format to exchange graphics, and there was a need to have the file size be as small as possible due to the minimum bandwidth available at the time. The development of the GIF addressed both issues.

The technology behind the GIF, using the same compression scheme used in programs like ZIP in a lossless fashion, which means that no image quality is lost from the compression. The compression in GIFs uses an algorithm called LZW.

All browsers support the GIF format. Initially, most color images and backgrounds on the Web were GIF files. Because colors in the graphic are limited to a palette of 256 hues, the GIF format is best suited for clip art and diagrams. The GIF format is not practical for detailed photographs. At the time, the GIF file

the format was created, the 256 color limitation was not an issue, as most monitors were only able to display 256 colors.

The JPEG graphic format

The JPEG format, named after the group that wrote the standard, the Joint Photographic Experts Group, was created so that actual color, 24-bit graphics could be contained in smaller files. File names are used with the file extension JPEG. The JPEG format became the preferred choice for use with full-color photographs since it can display 16.7 million colors compared to GIF images that are limited to 256 colors.

The JPEG reduces graphics of photographic color drop better than playing file formats like GIF, and it preserves a high degree of color accuracy. The image creator can specify image quality in trade for file size; the smaller the file size, the more information is lost, and the further the JPEG image will be from the original.

The PNG graphic format

The PNG format, pronounced ping, is endorsed by the W3C, World Wide Web Consortium, as the replacement for GIF format. The Portable Network Graphics file is a bit-mapped graphics format similar to GIF in that the file compresses the graphic without losing any data. PNG files can work with 256 colors or 16.7 million colors, a distinct advantage over the GIF format.

The catalyst for creating the PNG format was to develop a form that does not use the LZW data squeezing algorithm applied in the GIF but uses a patent and license-free file compression. Unisys patented the LZW data compression algorithm, and they had threatened to charge a royalty fee for its use. Although the development of the PNG format began in 1996, support has come slowly as web browsers and software developers have gradually embraced the format. Currently, all common web browsers and most graphics editors support the PNG format.

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