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DRAFT - Need to update
DRAFT - Need to update
Digital video refers to the capturing, manipulation, and storage of moving images that
can be displaced on computer screens (The Lycos Tech Glossary, 1999). This requires
that the moving images be digitally handled by the computer. Computers are digital systems and do not process images the way the human eye does.
Common Video Formats
MPEG4 is a file format that is commonly used to store media types defined by the ISO/IEC Moving Picture Experts Group, though it can store other media types as well. (.mp4)
M4V file format is a video file format developed by Apple and is very close to MP4 format. The differences are the optional Apple's DRM copyright protection, and the treatment of AC3 (Dolby Digital) audio which is not standardized for the MP4 container. (.mv4)
AVI stands for Audio Video Interlaced. It is one of the oldest formats. It was
created by Microsoft to go with Windows 3.1 and it’s “Video for Windows” application. (.avi)
MOV format, created by Macintosh, is the proprietary format of the QuickTime
application. It can also run on PCs. (.mov)
Audio
Audio
An audio file format and audio codec (compressor/decompressor) are two very different things. Audio codecs are the libraries that are executed in multimedia players. The audio codec is actually a computer program that compresses or decompresses digital audio data according to the audio file format specifications. For example, the WAV audio file format is usually coded in the OCM format, as are the popular Macintosh AIFF audio files.
Audio Formats can be broken down into three main categories. Uncompressed formats, lossless compression formats, and lossy compression.
Uncompressed audio formats (often referred to as PCM formats) are just as the name suggests — formats that use no compression. This means all the data is available, at the risk of large file sizes. A WAV audio file is an example of an uncompressed audio file.
Lossless compression applies compression to an uncompressed audio file, but it doesn't lose information or degrade the quality of the digital audio file. The WMA audio file format uses lossless compression.
Lossy compression will result in some loss of data as the compression algorithm eliminates redundant or unnecessary information — basically it tosses what it sees as irrelevant information. Lossy compression has become popular online because of its small file size, it is easier to transmit over the Internet. MP3 and Real Audio files uses a lossy compression.
Common Audio Formats
MP3 is the name of the file extension and also the name of the type of file for MPEG, audio layer 3. Layer 3 is one of three coding schemes (layer 1, layer 2 and layer 3) for the compression of audio signals. (.mp3)
AAC was developed to improve upon the MP3 audio format, and uses a more advanced form of compression. According to some listening tests, AAC files encoded at lower bitrates (like 96 Kbps) sound as good or as better than MP3s encoded at higher bitrates (like 128 Kbps) despite their smaller size. The current version of the AAC codec was developed as part of the MPEG4 standard. Versions of AAC are used by Apple in their popular iTunes® Store, as well as Sony in their PlayStation®3 game consoles. Files may appear with the ".m4a" or ".mp4" filename extension. Songs with DRM (digital rights management) purchased from the iTunes Store usually have an ".m4p" extension (with the "p" at the end to denote "protected").
WMA short for Windows Media Audio, WMA is a Microsoft file format for encoding digital audio files similar to MP3 though can compress files at a higher rate than MP3. (.wma)
WAV is the format used for storing sound in files developed jointly by Microsoft and IBM. Support for WAV files was built into Windows 95 making it the de facto standard for sound on PCs. WAV sound files end with a .wav extension and can be played by nearly all Windows applications that support sound.
MIDI short for musical instrument digital interface, MIDI is a standard adopted by the electronic music industry for controlling devices, such as synthesizers and sound cards, that emit music. At minimum, a MIDI representation of a sound includes values for the note's pitch, length, and volume.
Image
Image
Image file formats are standardized means of organizing and storing digital images. Image files are composed of either pixels, vector (geometric) data, or a combination of the two. 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.
Lossy vs. Lossless compression
You will often hear the terms "lossy" and "lossless" compression. A lossless compression keeps all information. In contrast, lossy compression discards some information in the image in order to achieve smaller file size.
Number of colors
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 video cards would support only 16 fixed colors. Later cards would display 256 simultaneously, any of which could be chosen from a pool of 224, or 16 million colors. New cards devote 24 bits to each pixel, and are therefore capable of displaying 224, 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 often called TrueColor.
Common Image Formats
TIFF is, in principle, a very flexible format that can be lossless or lossy. The details of the image storage 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. Consequently, file sizes are quite big.
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 256 colors from a pool of 16 million. If the image has fewer than 256 colors, GIF can render the image exactly. It also supports animations and allows a separate palette of 256 colors for each frame.
JPG is optimized for photographs and similar images that contain many colors. It can achieve astounding compression ratios even while maintaining very high image qualityJPG works by analyzing images and discarding kinds of information that the eye is least likely to notice. It stores information as 24 bit color. 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.
XCF eXperimental Computing Facility, is the native image format of the GIMP image-editing program. It supports saving each layer, the current selection, channels, transparency, paths and guides for editing in GIMP. When finished editing export the image as either a GIF, JPG, or PNG.
Image Format Usage
TIFF is usually the best quality output from a digital camera. TIFF means better quality, but the file size is huge compared to even the best JPG setting, and the advantages may not be noticeable. Do not use TIFF for web images. They produce big files, and more importantly, most web browsers will not display TIFFs.
JPEG is the format of choice for nearly all photographs on the web. You can achieve excellent quality even at rather high compression settings. I also use JPG as the ultimate format for all my digital photographs. When editing a photo use the editing software's proprietary format until finished, and then save the result as a JPG.
Digital cameras save in a JPG format by default. Switching to TIFF improves quality in principle, but the difference is difficult to see. Shooting in TIFF has two disadvantages compared to JPG: fewer photos per memory card, and a longer wait between photographs as the image transfers to the card.
Never use JPG for line art (consisting entirely of lines, without any shading). On images such as these with areas of uniform color with sharp edges, JPG does a poor job. These are tasks for which GIF and PNG are well suited.
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