Chapter 1 Information Representation 1.04 Video • is an electronic medium for the recording, copying and broadcasting of moving visual images characteristics of video streams. 1.04 Video • Is a sequence of still photographic images which are displayed in sequence. • The frequency with which they are displayed gives the appearance of continuous motion. Number of frames per second • Frame Rate – • The number of still pictures per unit of time of video, ranges from six – eight frames per second (old mechanical camera) or 120 or more frames per second (new professional cameras) • the frequency with which video frames are displayed. • 25 frames per second or higher – acceptable to human eye. Number of frames per second • Small frame rate means like seeing a slide show (1 image at a time) but higher frame rate, better animation flow • How about for computer games? 1.04 Video • Videos can be represented as progressive encoding or interlaced encoding 1.04 Video • Progressive Encoding • A system which stores the data for an entire frame and displays all the frame data at the same time. • This means that the frame rate will be number of pictures displayed per second. • Example: traditional film (where still pictures are moved in rapid succession) 1.04 Video • Interlaced Encoding • The data from a single frame is encoded as two separate fields; one containing the data for even number of rows and the second frame has the data for odd numbered of rows. • Called Interlaced because the image is rendered by switching between the even field and odd field. • Normally used if bandwidth is little 1.04 Video • Interlaced Encoding • Example: video content using DVD players, set – top boxes, other home electronic devices like TV • As the half images of interlaced are processed quicker than a progressive capture, there is less time for the subject to move within the capture time and so the movement can be crisper and cleaner. Which one is better? • Computer monitors display video progressively, one still or frame after the other, so when you get an interlaced recording playing on a progressive monitor, things can begin to fall apart and weird lines can become apparent, particularly with fast movement as the progressive playback attempts to cope with the interlaced image. • SO, filmmakers normally used progressive encoding, BUT, if you record something fast (sports), interlaced is better.
