image sequences john h. krantz hanover college. outline slideshows why presenting using redirects...
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Image Sequences
John H. Krantz
Hanover College
Outline
SlideshowsWhy
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
Original Loftus Eye Witness testimony was done this way
How?One easy way – use redirects
Here is an example
Avi is ~5 meg uncompressed, a t 161 kb compressed but louse image quality images are ~35 kb each
Previous Student Slideshows
Here are the work of previous students
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>
Make A slide show
Edit in Text editorJust edit new page for link
Change image shown
Use Save as
Remove meta tag for last image
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
Computer Video
Most Update rates are 10-15 frames/sec
5 fps 10 fps 15 fps
Probably not enough for speech and subtle facialexpressions.
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 valueNotice difference between flicker and frame update rate. Wagon wheel effect.
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
Differences in Persistence
Fast motion will be less clean on an LCD screen
General Video Issues
Image sizeKeep it small
320 x 240 is not uncommon
Image color depthNormally full color
Video LengthThe shorter the better
This file is ~ 5.5 meg in QuickTime and it is 17 seconds
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
Acquiring with a Digital Camera
Find format of your video camera mine is QuickTime
Can use digital zoomoriginal camera images are much larger than movie images so will be shrunk down
And digital zoom is before movie image
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 sizeBut image quality may be reduced to get on web
Editing with QuickTime Pro
Open more than one
BasicsOpens 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
QuickTime Pro Interface
Playback head
In markerOut marker
Selected region
Basic Editing
Selecting a region to editUse guides at bottom
Called In and Out Markers
Selected region is darkened
Arrow keys to fine tune
Cut and Paste operationPaste is at playback head
Adding Tracks
Copy as beforeUse Edit: Add – adds the video track
Use Edit: Extract TracksThen Edit: Add
Can extract sound this way to a movie
Can add scaled so new track is not length of old movie
Deleting Tracks
Use Edit: Delete Tracks
Remove any unwanted sound from video
More Advanced Editing with QuickTime Pro
Adding text to beginningMake 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
More Advanced Editing with QuickTime Pro
Overlaying TextUse a gif file with a transparent background
Use a text fileFile: 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
More Advanced Editing with QuickTime Pro
Filtering portions of movieDelete regions do not want to filter
Use the export function
Click on Options
Click on Filter
Pick pattern
Use cut and paste to reassemble
Saving for Web
Format:You must compress
Uncompressed files will be very large
Lead very slow download
DurationFor same reason, keep videos short
To Stream or Not to Stream
SteamingStarts sooner
Can be large files
Can stop
Relatively lower quality and quality depends on connection
General Protocol RTP/RTSP
Regular DeliveryWait for entire file
Keep to small files
Keeps Speed
Relatively better quality, but quality depends upon monitor and format
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
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/
Assignment
Have Fun!
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