chap55

DIGITAL MEDIA FUNDAMENTALS

Explain the various file format such as PDF, TIFF, JPEG , MP3, MPEG and its compression

methodology and its compression methodology.



In This Chapter, you’ll learn on: Describe image compression such as:

o Monochromeo Grayscale compressiono GIF compressiono JPEG compression

Describe audio compression such as:o Lossless compressiono Lossy compression

Describe video compression such as:o MOVo AVIo WMV



Raw Multimedia Data Representation

What exactly is Raw Multimedia Data Representation? In simple terms with reference to Digital Imaging it literally means "raw" as in "unprocessed". A RAW file contains the original image information as it comes off the sensor before in-camera processing so you can do that processing afterwards on your PC with special software. RAW files are huge in file size and contain redundant data



Image CompressionMonochrome/Grayscale Compression

A single color, monochrome usually refers to a black-and-white image, also referred to as line art or bitmap mode. Grayscale refers to an image output in shades of gray.

An image representation in which each pixel is represented by a single sample value, representing overall luminance on a scale from black to white.

A conversion from color to grayscale will reduce the file size as the file has only one channel. An RGB color image will have a separate channel for Red, Green & Blue.



GIF Compression GIF, which stands for Graphics Interchange Format, is a

lossless method of compression. All that means is that when the program that creates a GIF squashes the original image down it takes care not to lose any data. It uses a simple substitution method of compression.

If the algorithm comes across several parts of the image that are the same, say a sequence of digits like this;

1 2 3 4 5, 1 2 3 4 5, 1 2 3 4 5 It makes the number 1 stand for the sequence 1 2 3 4

5 so that you could render the same sequence as 1 1 1.



GIF Compression Obviously this saves a lot of space and it stores

the key to this (1 = 1 2 3 4 5) in a hash table, which is attached to the image so that the decoding program can unscramble it.

The maximum compression available with a GIF

therefore depends on the amount of repetition there is in an image. A flat colour will compress well - sometimes even down to one tenth of the original file size - while a complex, non-repetitive image will fare worse, perhaps only saving 20% or so.



JPEG Compression This file compression method can obtain a very

high compression ratio if it is used with detailed photographic images, which was its intended use.

Part of JPEG’s success in high compression is due

to the fact it is a "lossy" compression method, meaning the compression results in the loss of some data that is determined to be unimportant or unnecessary.



JPEG Compression JPEG is highly flexible in that it allows you to make

a "quality" setting, which determines the amount of loss that will occur and affects the size of the resulting compressed file. The JPEG algorithm takes into account the fact that the human eye is more sensitive to changes in brightness than to number of colors.

Rather than saving the color data from each pixel in an image, it saves information on the rate of change of color, or "frequency information."



Audio Compression

An audio file format is a file format for storing audio data on a computer system. There are many file formats for storing audio files.

There are two categories of audio file formats: lossless formats e.g.WAV, PCM lossy format e.g. MP3, Windows Media Audio

(WMA) .



Audio Compression Lossy audio formats are based on human audio

system, which leave out sounds that human cannot or can hardly hear e.g. MP3.

In lossless audio formats no data or quality is lost in the compression - when uncompressed; the data will be identical to the original. It will be best used to keep the music's original quality.

Lossless compression of sound is not as widely used as lossy compression can provide a much greater data compression ratio, with nearly the same apparent quality.



MOV, AVI and WMVApple QuickTime (MOV)QuickTime is the multi-platform industry-standard multimedia architecture used by software tool vendors and content creators to create and deliver synchronized graphics, sound, video, text and music. Developed by Apple, it has become one of the most widely used formats on the World Wide Web.

QuickTime movies can be compressed using software packages such as Adobe Premiere of Media Cleaner Pro to sizes that are feasible for use over the Internet. Most CD-ROMs use QuickTime movies and there are several sites on the Internet that make use of the format. The images are of higher quality, but file sizes can be significantly larger than other video storage formats.



MOV, AVI and WMVMicrosoft AVI Video (AVI)

AVI is a format for video files that offers minimal compression ability and is available on the Windows platform only. It is widely used on the World Wide Web.

Because AVI is not compressed with one specific codec, rather it is a file that can be compressed by any one of hundreds of codecs like DivX, MPEG-4v2, Indeo 3.2, Cinepak to name a few, it makes the file hard to play. In Windows it is rather easy to play an AVI file IF you have the correct codec installed. There are a whole lot of Windows applications available that can play AVI files like Windows Media Player. Unfortunately if you do not have the codec needed to play the file Windows Media Player will not be able to play it.



MOV, AVI and WMVWindows Media Video (WMV) Windows Media Video (WMV) is a video compression format developed by Microsoft. The first version of the codec, WMV 7, was introduced in 1999. Originally, it was designed for Internet streaming applications, as a competitor to RealVideo. To date, its main competitors are MPEG-4 AVC, AVS, RealVideo, and MPEG-4 ASP. Software that can play WMV files includes Windows Media Player, RealPlayer, MPlayer, The KMPlayer, Media Player Classic and VLC Media Player.

chap55

Technology

world wide web

file format

lossless compression

gif compression

file size

compression methodology

quicktime movies

file