Digital Image Formats Explained
Digital formats refer to the different file types used to encode digital images. Digital files can be very large initially. If left in the original state, with no compression, they can occupy considerable hard drive space and take a long time to download over the Internet. Because the types of images that are captured digitally vary from photographic to illustrative, there are many different file types for encoding. This week, we offer a series of tips on digital image formats and terminology.
This Week's Tips
Data Compression Reduces Image File Size (Monday)
Utilize data compression to reduce the size of image files used in class. Compression ”squeezes” files by removing data deemed unnecessary by the compression software. In the case of images, the “unnecessary” data is usually pixilated color. Compression is used to increase the number of files that can be saved to removable discs, such as CD-ROM and DVD, or to computer hard drives. It also enhances the Internet experience by reducing the time it takes to download images and other file types. Compression is typically applied to images, sound, and digital video files, but can also be applied to other multimedia files.
Lossy and Lossless Compression Serve Different Purposes (Tuesday)
Understand the difference between the two types of compression: lossy and lossless. Lossy compression discards, or degrades, some data from a digital file image to limit the file’s size. It degrades the quality of the image. Lossless compression discards no information from a digital file image. It makes no compromise in the quality or accuracy of the file image. Base your decision about which type of compression to use on the technology you will use to display it and the purpose of its use.
JPEG Files Work Best for Photographic Images (Wednesday)
JPEG files are the standard, lossy compression format designed for digital photographic images. It is the optimal file format for storing photographic images with full color or gray scales and continuous variations in color images. JPEG can be read by virtually any browser or image reader. It is the best format when file size is a concern. However, JPEG is not the best choice for images with lettering, cartoons, line art, drawings, or black and white images as it does a poor job with uniform color and sharp edges. JPEG stands for Joint Photographic Experts Group.
GIF Files Work Well for Flat Images (Thursday)
GIF files are the standard lossless compression format. They are designed for flat images and work well for text and illustrations. This compression type works best for images with limited distinct colors, typically fewer than 256. It is the file choice for line drawings, simple cartoons, and computer generated images. The GIF file type has improved Web page interface design by allowing for sleek graphically designed pages that are quick to download. GIF stands for Graphic Interchange Format.
PNG Files Create Realistic Images (Friday)
PNG is a format that recovers images exactly. It is superior to GIF because it supports 16 million colors with a lossless compression known as deflation. PNG is used on images with large areas of exactly uniform color. PNG images almost always look great. Unfortunately, PNG images are not readable by all browsers and therefore are not always the best choice for Web sites. PNG stands for Portable Network Graphics.