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Image Sequences

Image Sequences. John H. Krantz Hanover College. Outline. Slideshows Why Presenting Using Redirects Video (if interested) Background Delivering in a Webpage. Why Slideshows. Example 1 Indicate sequence of events Carries sense of change From Billy – sense of momentum in photo

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Image Sequences

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  1. Image Sequences John H. Krantz Hanover College

  2. Outline • Slideshows • Why • Presenting Using Redirects • Video (if interested) • Background • Delivering in a Webpage

  3. Why Slideshows • Example 1 • Indicate sequence of events • Carries sense of change • From Billy – sense of momentum in photo • Original Loftus Eye Witness testimony was done this way • How? • One easy way – use redirects

  4. Here is an example • Avi is ~5 meg uncompressed, a t 161 kb compressed but louse image quality images are ~35 kb each

  5. Previous Student Slideshows • Here are the work of previous students

  6. Code for redirect <html> <head> <title>Image Sequence</title> <META HTTP-EQUIV="refresh" CONTENT="3; URL=page01.html"> • Number is number of seconds before redirect </head> <body> <p> This will change in 3 seconds, about</p> <p align = "center"> <img border="0" src="Bobby0000.jpg" width="512" height="384"></p> </body> </html>

  7. Make A slide show • Edit in Text editor • Just edit new page for link • Change image shown • Use Save as • Remove meta tag for last image

  8. Motion Reproduction • Frame rates of monitors far exceed what is needed for movement update • NTSC video: 30 updates per second • Movies: 24 updates per second • Most web video 10 to 15 frames/sec

  9. Computer Video • Most Update rates are 10-15 frames/sec 5 fps 10 fps 15 fps Probably not enough for speech and subtle facialexpressions.

  10. Flicker • Critical threshold of flicker rates is about 60 Hz in the fovea • But gets higher for larger stimuli • Recommended flicker rates between 66 Hz and 120 Hz (Bridgeman, 1998) • Most monitors are adequate in this value • Notice difference between flicker and frame update rate. • Wagon wheel effect.

  11. Stimulus Duration • Pixels are not on continuously during a frame • In part this is necessary for clean motion • Typical CRT phosphors last about 4 msec. (Bridgeman, 1998) • On LCD and other technologies, persistence is longer • Makes motion less clean but flicker less noticeable

  12. Differences in Persistence Fast motion will be less clean on an LCD screen

  13. General Video Issues • Image size • Keep it small • 320 x 240 is not uncommon • Image color depth • Normally full color • Video Length • The shorter the better • This file is ~ 5.5 meg in QuickTime and it is 17 seconds

  14. General Video Issues • Frame rate: recall difference between apparent motion and flicker • 10 to 15 is really fine for most cases • And best you can expect on web

  15. Acquiring with a Digital Camera • Find format of your video camera • mine is QuickTime • Can use digital zoom • original camera images are much larger than movie images so will be shrunk down • And digital zoom is before movie image

  16. Acquiring with a Digital Camera • Hold camera still or not? • Movies are limited in duration • mine is 30 sec or size of disk for 320x240 • It is 120 sec if 160x120 • Image quality is reasonably good if presented in original size • But image quality may be reduced to get on web

  17. Editing with QuickTime Pro • Open more than one • Basics • Opens MOV, mpg, avi, mp3, etc. • Get Movie Information on Movie Menu (ctrl-j in Windows) • Tracks: separate slices of information: played at same time as other tracks • Look under the Edit menu

  18. QuickTime Pro Interface Playback head In marker Out marker Selected region

  19. Basic Editing • Selecting a region to edit • Use guides at bottom • Called In and Out Markers • Selected region is darkened • Arrow keys to fine tune • Cut and Paste operation • Paste is at playback head

  20. Adding Tracks • Copy as before • Use Edit: Add – adds the video track • Use Edit: Extract Tracks • Then Edit: Add • Can extract sound this way to a movie • Can add scaled so new track is not length of old movie

  21. Deleting Tracks • Use Edit: Delete Tracks • Remove any unwanted sound from video

  22. More Advanced Editing with QuickTime Pro • Adding text to beginning • Make any graphic • Resize to movie size so know how it will look • Select al (ctrl-A) • Then cut and paste to beginning • Another paste for each additional frame

  23. More Advanced Editing with QuickTime Pro • Overlaying Text • Use a gif file with a transparent background • Use a text file • File: Import • Any .txt • Press Option button • Select keyed text • Change background to white and foreground to text color • I like changing it to bold • Add tracks as before

  24. More Advanced Editing with QuickTime Pro • Filtering portions of movie • Delete regions do not want to filter • Use the export function • Click on Options • Click on Filter • Pick pattern • Use cut and paste to reassemble

  25. Saving for Web • Format: • You must compress • Uncompressed files will be very large • Lead very slow download • Duration • For same reason, keep videos short

  26. Steaming Starts sooner Can be large files Can stop Relatively lower quality and quality depends on connection General Protocol RTP/RTSP Regular Delivery Wait for entire file Keep to small files Keeps Speed Relatively better quality, but quality depends upon monitor and format To Stream or Not to Stream

  27. Streaming vs. HTTP Fast Start • HTTP Fast Start is a feature of QuickTime • Allows playing after part of file downloaded • Fewer stops • No special software • Still keep files relatively small • Some loss of image quality

  28. Embedding a QuickTime Movie in a Web Page <p align="center"> <OBJECT CLASSID="clsid:02BF25D5-8C17-4B23-BC80-D3488ABDDC6B" WIDTH="480" HEIGHT="376“ CODEBASE="http://www.apple.com/qtactivex/qtplugin.cab"> <PARAM NAME="src" VALUE="start.mov"> <PARAM NAME="controller" VALUE="false"> <PARAM NAME="target" VALUE="myself"> <PARAM NAME="href" VALUE=“clip.mov"> <EMBED WIDTH="480" HEIGHT="376" CONTROLLER="false" TARGET="myself" HREF=“clip.mov" SRC="start.mov" BGCOLOR="FFFFFF" BORDER="0" PLUGINSPAGE="http://www.apple.com/quicktime/download/indext.html"> </EMBED> </OBJECT> </p> Example: http://ati.fullerton.edu/jkrantz/session3/video/

  29. Assignment • Have Fun!

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