notes for March 30 * Review * We've seen * Text (.txt) * Images (.jpeg, .gif, .png) * Audio (.wav, .mp3) * For each type of data you can expect * raw data file formats ( .tiff photographs, .wav recordings) * compressed raw data formats (mp3, jpeg) * cartoon-ish formats ( .gif, .midi ) * Applications for editing the data * select pieces of data to work on * layers that "overlay" in various ways * variety of filters and effects * opensource (Gimp, Audacity) vs commercial (Photoshop, ...) * take practice to master * With a web browser * files have extensions to indicate type of data * links to download file or * tags within HTML display pictures/sounds * images * common * .jpeg (photos), .gif (cartoons) * .png (better cartoon format) * supported by the browser itself * typical file size is 50k for 640x480 jpeg raw data is 640x480 x 24 bits/pixel = 7 MBytes, so compression is 20x (Note: 1 MB = 1024 * 1024 * ( 8 bits/Byte ) .) * audio * less common * companion plugins or applications do playing * tags are inconsistent between browsers * typical file size is 2MB for 2.5 minute mp3 raw data is 145 sec * 44100 /sec * 16 bits * 2 channels = 24 MB, so compression is 10x * Network speeds (Note: 1 Mbps = 1024*1024 bits/second = 1 MB / 8 sec = 7.5 MB/minute) * voice phone : 64 Kbps = 0.0625 Mbps * T1 : 1.5 Mbps (college has about 1/2 T1 to world right now) * ethernet : 10 Mbps typically (100 Mbps is becoming more common) * Streaming * "real-time" audio or video (i.e. broadcast) * The tradeoff is between * raw : requires big bandwidth * compressed : requires big cpu to encode/decode on the fly. * Quick quiz : * What bandwidth do you need to stream audio? * What does "16 bits/sample" audio mean? * What does "24 bits/pixel" mean? Why 24? * What is YUV and how does it differ from RGB? * What's the difference between "lossy" and "lossless" compression? * What sorts of tricks are used to do compression on (a) text, (b) images, (c) audio ? Now on to... * Video/Film/Animation * lots of history and geography in how things are done * many encoding formats, broadcast formats, file formats, ... * TV * NTSC (US) see http://www.ntsc-tv.com/ntsc-index-01.htm * analog * 4:3 aspect ratio * 30 frames/sec (well, OK, 29.97) * interlaced (even lines drawn in 1/60 sec; odd lines next 1/60) * frame rate from 60Hz electrical power in US. * 480 vertical lines * Y (luminance), UV (chrominance) color is B/W compatible * 6MHz bandwidth, AM modulation; audio is FM * Broadcast VHF (Very High Freq) is 30-300MHz (10-1meter) * PAL (Europe) * 25 frames/sec * 625 vertical lines * composite video format before modulated onto an RF carrier YUV (Y = luminance, UV = color information) what you get from the yellow jack of a VCR; red/white are stereo sound (for video games, an RF modulator often used to send the composite signal to channel 3 or 4. This means the vido signal has RF (1) added in and then (2) taken out by the TV. Can you say "extra noise"?) * component video * better signal * RGB or YUV (eg. Y, R-Y, B-Y) in three separate wires, * sometimes referred to as 4:2:2 in terms of allocated bits (4 for Y, 2 for U,V on even lines, 2 for UV on odd lines) (DVD's often use 4:2:0, with color for odd lines interpolated.) * S-Video * quality between composite and component * uses 2 signals Y (b/w) and C (color UV). * typically 4-pin mini-DIN plug with 75 ohm termination impedence * Film : usually 24 frames per second * 35mm * basic film format for both still and motion pictures * unchanged since 1889; has holes (perforations) along edges * various ways to put images on film : * classic movie : 4 perforations / frame, vertically, aspect ratio is 4:3. * still : frame horizontal, 8 perf / frame * vistavision : like sill, 1.67 aspect ratio, never really caught on * cinemescope : (anamorphic) image compressed horizontally to fit on on the film horizontally, even though wide on screen with aspect ratio of 2.35 * today most are shot w/ 4 perf/frame and cropped top/bottom to get 1.85 or 1.67 aspect ratio * or even 3-perf with 16:9 HDTV format * 70mm is also shot today * audio for films is now stored several ways, including * SDDS (two strips beyond perforations) and * DTS (on a separte CD which is synced to the film) * A place to start : playing around animated gifs * Gimp * put animation cells in individual layers * name layers things like "Frame 1 (50ms) (replace)". * the first stuff in () is the time to show that frame; * the second is "replace" or "combine" depending on how it should be drawn on previous frame. * "save as GIF..." gives option of saving multiple layers as animation. * Filters/Animation/Animation_Playback lets you see it. * Filters/Animations/Animation_Optimize changes layers draw with to "combine" sequentially; better compression. * animation frames run from last (background) to top in the stack. (?) * Script-Fu/Animators/ * SpinningGlobe : map an image to a rotating sphere * Rippling : like a flag in the wind * GAP - Gimp Animation Package * lots more bells and whistles that I haven't installed or tested het. * tutorial: http://jimmac.musichall.cz/tutor2.php3 * Note: Gimp 2.0 was out March 26 2004; see www.gimp.org * Stop motion * like animation but with clay, legos, puppets, ... * several ways to do this * our digital cameras will shoot one frame at a time, I think * a digital still camera * Other web animation : * Flash / MacroMedia Shockwave / .swf files * commerical application installed on media lab *