Image Representation03-11-2009

• jpg, gif, tif, png

• video formats, container

• YouTube

Susen Rabold

Image Compression Formats

JPG or JPEG

GIF

TIF or TIFF

PNG

Joint Photographic Expert Group

Graphics Interchange Format

Tagged Image File Format

Portable Network Graphics

JPG

RGB - 24 bits

Grayscale - 8 bits

JPEG always uses lossy JPG compression, but its degree is selectable, for higher quality and larger files, or lower quality and smaller files.

GIF

GIF uses lossless compression, effective on indexed colour. GIF files contain no dpi information for printing purposes.

Indexed colour - 1 to 8 bits

TIF

RGB - 24 or 48 bits

Grayscale - 8 or 16 bits

Indexed colour - 1 to 8 bits

For TIF files, most programs allow either no compression or LZW compression (lossless, but is less effective for 24 bit color images).

PNG

RGB - 24 or 48 bits

Grayscale - 8 or 16 bits

Indexed colour - 1 to 8 bits

PNG uses ZIP compression which is lossless.

PNG was created to improve upon and replace GIF as an image-file format not requiring a patent license.

Lossy vs Lossless

Lossy Lossless

Lossy Compression In a lossy compression scheme, as the name implies, some of the original information is discarded when it is compressed. Therefore, it is impossible to produce an exact replica of the original audio signal when the audio is played. There are many different schemes of lossy compression available. These schemes generally provide varying compression ratios. The most popular of these, the MPEG Layer 3 (MP3) format, is commonly employed with compression ratios of up to ten to one. All lossy compression schemes add artifacts to the compressed audio. Artifacts are small imperfections created by the loss of the actual audio data. Although its quality may not seem that poor, the audio that has been processed by a lossy digital compressor is no longer "CD Quality".

Lossless Compression

Lossless compressors produce an exact replica of the original source. For example, the zip file format produced by the Winzip program on a PC produces exact copies of the original material that was encoded within the zip file. Fortunately, there is at least one lossless compression scheme available for Windows PCs. It's known as Shorten, an audio format that creates an exact clone of the original source. Lossless compression is the only way to preserve the "CD Quality" level of your program material.

dpi

dots per inch

Pixel (picture element)Smallest item of information in an image. Pixels are normally arranged in a 2-dimensional grid, and are often represented using dots or squares. Each pixel is a sample of an original image, where more samples typically provide more-accurate representations of the original. The intensity of each pixel is variable; in colour systems, each pixel has typically three or four components such as red, green, and blue, or cyan, magenta, yellow, and black.

video compression

MPEG

Flash

container

encoder

Moving Picture Expert Group

(Adobe)

codec

MPEGMPEG-2The standard on which such products as Digital Television set top boxes and DVD are based;

MPEG-4The standard for multimedia for the fixed and mobile web;

MPEG-4 H.264/MPEG-4 AVC is a standard for video compression, while .m4a or .mp4 for

audio.

H.264 is most popular for its use on Blu-ray Disc, HD DVD and videos from the iTunes Store.

AVC = Advanced Video Coding

MPEG-2 H.263 for video, .mp3 for audio.

The standard on which such products as Video CD and MP3 are based

Flash

Adobe formerly Macromedia.

Compression format like MPEG.

.flv and .f4v are container formats.

Container: H.264 (newer)/VP8 (open source decoder) or H.263 (previously) for video

Speex (newer) or MP3 (still/previously) for audio

CODECS

When it looks like that MPEG-4 and Flash are using the same compression

what’s the difference??

How the container is programmed and how information is decoded.

Main difference: Flash allows use of vectors, which makes it more interesting

for e.g. advertisement, since you can easier include animation and while MPEG4 good for watching films, Adobe Flash is better to

integrate in websites.

Important: Every video format has their own codecs, which means you need different decoders.

YouTubeUse of Adobe Flashallows the site to display videos with quality comparable to more established video playback technologies (such as Windows Media Player, QuickTime, and RealPlayer) that generally require the user to download and install a web browser plug-in to view video content. Viewing Flash video also requires a plug-in, but market research from Adobe Systems has found that its Flash plug-in is installed on over 95% of personal computers.

YouTube accepts videos uploaded in most formats, including .WMV, .AVI, .MKV, .MOV, MPEG, .MP4, DivX, .FLV, and .OGG. It also supports 3GP, allowing videos to be uploaded directly from a mobile phone.

Briefly: YouTube issues

Inappropriate content

Blocked in some countries:

Republic of China, Morocco, Thailand, Turkey.

Example for privacy issue and problems with lawsuits :In July 2008, Viacom won a court ruling requiring YouTube to hand over data detailing the viewing habits of every user who has watched videos on the site. The move led to concerns that the viewing habits of individual users could be identified through a combination of their IP addresses and login names. The decision was criticized by the Electronic Frontier Foundation, which called the court ruling "a set-back to privacy rights". U.S. District Court Judge Louis Stanton dismissed the privacy concerns as "speculative", and ordered YouTube to hand over documents totalling around 12 terabytes of data. Judge Stanton rejected Viacom's request for YouTube to hand over the source code of its search engine system, saying that there was no evidence that YouTube treated videos infringing copyright differently.

source wikipedia

http://news.cnet.com/Viacom-sues-Google-over-YouTube-clips/2100-1030_3-6166668.html

Animated video

Lab next week: http://www.blender.org/

http://www.blender.org/education-help/quickstart/

http://www.youtube.com/watch?v=Gp_5Wuwv1DE&feature=related

http://www.youtube.com/watch?v=iIOlbZW5qfY