Dynamic Media on the Web John H. Krantz Hanover College

Outline Slideshows Creating with ImageJ Presenting Using Redirects Video Background Editing with QuickTime Delivering in a Webpage

Why Slideshows Example1Example1, Example 2Example 2 Indicate sequence of events Carries sense of change Think of Loftus early eyewitness studies Billy – sense of momentum in photo

Creating Slideshows with ImageJ Stacks Sequence of images to be played Found under Image menu Open the desired sequence in order Images must all be the same size Image: Stacks: Convert Images to Stack

Editing Stacks Can add and remove images (a Slice) under the same menu Many other editing options do not work on stacks so edit images before you make stack. Save as…Image Sequence Give convenient name in numerical order

Why do this in ImageJ Cannot play in ImageJ so why all of this work? Can edit images first Can preview easily (but only with 1 frame per second at slowest) Can give convenient name Put in folder of choice

Can save as Movie Stack Menu Can control frame rate under: Image: Stacks: Animation Options Determine frame rate Get AVI writer plugin to save as a movie or a more current version of ImageJ (will be under Save As) File will be huge.

Here is an example Avi is ~5 meg image is ~350 kb

Slideshows Can also do slideshows in web pages Here is an example Why? Can be much smaller – faster download Show sequence – convey more than single image Original Loftus Eye Witness testimony was done this way How? One easy way – use redirects

Code for redirect Image Sequence Number is number of seconds before redirect This will change in 3 seconds, about

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

A JavaScript Slide Show Click here Here is one that has different times for different images Use View Source to get the code

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 frames/sec 5 fps 10 fps 15 fps Probably not enough for speech and subtle facial expressions.

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 effectWagon 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 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

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 zoom original 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 size But image quality may be reduced to get on web

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

QuickTime Pro Interface Playback head In marker Out marker Selected region

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

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

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

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

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

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

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

To Stream or Not to Stream Steaming Starts sooner Can be large files Can stop Generally low quality General Protocol RTP/RTSP Regular Delivery Wait for entire file Keep to small files Keeps Speed Better quality

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