Digital download file types

These and many other file types are used to encode digital images. The choices are simpler than you might think. Part of the reason for the plethora of file types is the need for compression. Image files can be quite large, and larger file types mean more disk usage and slower downloads. Compression is a term used to describe ways of cutting the size of the file. Compression schemes can by lossy or lossless.

Another reason for the many file types is that images differ in the number of colors they contain. If an image has few colors, a file type can be designed to exploit this as a way of reducing file size. You will often hear the terms "lossy" and "lossless" compression. A lossless compression algorithm discards no information.

It looks for more efficient ways to represent an image, while making no compromises in accuracy. In contrast, lossy algorithms accept some degradation in the image in order to achieve smaller file size. A lossless algorithm might, for example, look for a recurring pattern in the file, and replace each occurrence with a short abbreviation, thereby cutting the file size.

In contrast, a lossy algorithm might store color information at a lower resolution than the image itself, since the eye is not so sensitive to changes in color over a small distance. Images start with differing numbers of colors in them.

The simplest images may contain only two colors, such as black and white, and will need only 1 bit to represent each pixel. Many early PC video cards would support only 16 fixed colors. Later cards would display simultaneously, any of which could be chosen from a pool of 2 24 , or 16 million colors.

Current cards devote 24 bits to each pixel, and are therefore capable of displaying 2 24 , or 16 million colors without restriction. A few display even more. Since the eye has trouble distinguishing between similar colors, 24 bit or 16 million colors is sometimes called TrueColor. Better modern cameras can capture even more colors. TIFF is, in principle, a very flexible format that can be lossless or lossy.

The details of the image storage algorithm are included as part of the file. In practice, TIFF is used almost exclusively as a lossless image storage format that uses no compression at all.

Most graphics programs that use TIFF do not compression. Consequently, file sizes are quite big. Sometimes a lossless compression algorithm called LZW is used, but it is not universally supported. PNG is also a lossless storage format. However, in contrast with common TIFF usage, it looks for patterns in the image that it can use to compress file size.

The compression is exactly reversible, so the image is recovered exactly. GIF creates a table of up to colors from a pool of 16 million. If the image has fewer than colors, GIF can render the image exactly. When the image contains many colors, software that creates the GIF uses any of several algorithms to approximate the colors in the image with the limited palette of colors available.

Better algorithms search the image to find an optimum set of colors. Sometimes GIF uses the nearest color to represent each pixel, and sometimes it uses "error diffusion" to adjust the color of nearby pixels to correct for the error in each pixel.

GIF achieves compression in two ways. First, it reduces the number of colors of color-rich images, thereby reducing the number of bits needed per pixel, as just described.

Second, it replaces commonly occurring patterns especially large areas of uniform color with a short abbreviation: instead of storing "white, white, white, white, white," it stores "5 white. Thus, GIF is "lossless" only for images with colors or less. For a rich, true color image, GIF may "lose" JPG is optimized for photographs and similar continuous tone images that contain many, many colors.

It can achieve astounding compression ratios even while maintaining very high image quality. GIF compression is unkind to such images.

JPG works by analyzing images and discarding kinds of information that the eye is least likely to notice. It stores information as 24 bit color. Important: the degree of compression of JPG is adjustable. At moderate compression levels of photographic images, it is very difficult for the eye to discern any difference from the original, even at extreme magnification. Compression factors of more than 20 are often quite acceptable.

Better graphics programs, such as Paintshop Pro and Photoshop, allow you to view the image quality and file size as a function of compression level, so that you can conveniently choose the balance between quality and file size. RAW is an image output option available on better digital cameras. Though lossless, it is a factor of three of four smaller than TIFF files of the same image.

The disadvantage is that there is a different RAW format for each manufacturer, and so you may have to use the manufacturer's software to view the images. Some graphics applications can read some manufacturer's RAW formats. Sampling frequency, bit-depth, and monophonic or stereo, for example, are important characteristics of audio files.

A moving image recording with synched audio produced from either original analog or digital video formats. Pixel array, frame rate per second, aspect ratio, bit rate, field order, color space, and standard or high definition, for example, are important characteristics of video files. A high-resolution moving image recording, often with synched audio, produced from either original physical or digital formats.

Bit-depth, pixel array, frame rate per second, and color encoding, for example, are important characteristics of motion picture files. A DCP or Digital Cinema Package is a collection of digital files used to store and convey digital cinema audio, image and data streams. PDF files require the free Adobe Reader. The U. Enter Search Term s :. Still Image File A type of digital object that is created from the digitization of still image textual documents and photographs originals.

Video File A moving image recording with synched audio produced from either original analog or digital video formats.

Motion Picture File A high-resolution moving image recording, often with synched audio, produced from either original physical or digital formats. File Type To Be Determined.