The GIF, PNG, and JPEG formats are the most commonly used file formats on the World Wide Web today.
The PNG format (Portable Network Graphics) was developed in 1995 to replace the GIF (Graphics Interchange Format) format for two reasons. The first reason is that the GIF format is patented and developers using software implementing this format would be subject to royalties. The PNG format doesn’t have any patent so it can be read and written by software developers and webmasters without having to pay any royalties. The second reason is that a GIF image can only be saved as an 8 bit image, which basically means you are restricted to just 256 colours. PNG can be saved as an 8 bit, 24 bit - up to 64 bit! Also, PNG supports a much higher level of transparency whereas GIF images only allow one out of the 256 colours to be fully transparent.
A very popular feature of the PNG format that wins over a lot of folks is the alpha channel. A PNG image with the alpha channel feature is able to achieve 256 levels of transparency which means you can antialias text and images to allow sharp curves to look good against a changing background – drop shadows will fade nicely into the background, and any image can be created to take any shape or form.
From the standpoint of the graphic artist, the GIF and PNG format is very much the same – both use loss-less compression which means that once the image is saved there is no further decrease in the image quality or sharpness. This allows you to decompress, edit and recompress the image without degradation of image quality. However, benefits that PNG have over the GIF format is that PNG, in almost every case, compresses more efficiently and will be up to 20% smaller than a GIF file.
Another winning feature of the PNG format is its ability to adjust gamma based on the monitor settings. An image can be viewed the way it was intended to be viewed because the PNG format stores the gamma information in an image and the application reading the PNG takes note of that gamma information.
A significant disadvantage of both GIF and PNG formats is that they are not really good at compressing complex, natural images, especially images that come from photographs. This is where the JPEG format shines. The JPEG format (Joint Photographic Experts Group) has a more complicated compression and records an image by looking at areas, patterns and colours - the GIF and PNG record images by describing each pixel separately. With complicated, natural images, the GIF and PNG can take up to 10 times the space of a JPEG which is why the GIF and PNG are usually used for smaller images. In general, the JPEG is a really good format for compressing natural looking images into a very small size. Because a JPEG’s compression is so complex and it is not a perfect compression format – slight imperfections can arise in the decompressed image if used incorrectly. Examples of these imperfections are blurring around text and flat areas of colour. Other disadvantages to the JPEG format are that it is unable to include transparent areas and the image quality degrades each time a JPEG is resaved.
A general rule of thumb is to use the PNG and GIF format for basic images with limited numbers of solid, sharp areas of colour – basic images like logos, text, graphs, headings, buttons etc. Start using PNG over the GIF format as PNG has a lot more benefits and is now widely supported on the web. For complex, natural images like photographs, the JPEG format is your best bet.
About the Author
Anna Agnew is an author for The Computer Geek Custom Web Page Design. The Computer Geek is a web design company that prides itself in professional service at a fraction of the cost. The Computer Geek specializes in Custom Web Design, PHP & MySql and Ecommerce.