Introduction to Media for Webbased Research John H

Introduction to Media for Webbased Research John H. Krantz Hanover College Workshop on Web Research Centre for Affective Sciences, May 2008

Outline • • Background Graphics and Images Video Color and Lighting

The General Beast CRT LCD (Flat Panel)

Background • Screen formats are changing – Original: 4 x 3 (Width is 4 to Height's 3) – New (driven by HDTV) is 16 x 9

Screen Formats

Graphics vs. Images • Some definitions: mine for clarity here: – Graphics Def: computer generated or drawn by you. – Image: scanned, captured, take photograph or an graphic file not generated by you. – Difference: • In a graphic, you can directly manipulate the elements because you drew them – Sprites • In an image, you can manipulate pixels but not directly the elements. This has a great impact.

Images or Graphics on the Screen • Pixels: smallest picture element – Pixels are not screen dots!!! – Several dots (at least three, one of each color) make up each pixel) • Bitmat: An array of information that contains the information for the image. – – It is a 3 dimensional array Width x Height x 24 (8 for each color) So can be huge (. bmp and. tif or. tiff are most common bitmaps)

Graphic and Image Formats – Bitmap (bmp, PCT, Tiff) – big, not good for web – Graphic Interchange Format (Gif) can animate • 8 bits of color – palette or lookup table or LUT – no loss of spatial information • Can be some legal issues – make sure the generator legally can generate GIF’s • Generally best compression for simple graphics – bad for photos • Can generate transparent regions • Can Animate

Graphics and Image Formats – JPG • Generally better for images and photos • Spatial not color compression, can distort image spatially and more loss with each save • Now can animate as well.

Bitmapped vs. JPEG File Sizes Both images are the same relative size. 900 kb . JPEG High Quality ~700 kb

Image. J • Free at: http: //rsb. info. nih. gov/ij/index. html • Overview – Java program – Interface a bit awkward because it is free – Expandable via plug-ins • Covers all basic editing and many advanced - very advanced • Scientific quality image editor • Used in many technical applications • Plugins!

Gimp • Freeware photo editor that rivals Photoshop • Works with Layers, allows reediting • Download: http: //gimpwin. sourceforge. net/stable. html

Dynamic Media • Slideshows – Why – Presenting Using Redirects • Video – Background – Delivering in a Webpage

Why Slideshows Example 1; Example 2 Indicate sequence of events Carries sense of change Sense of momentum in photo Original Loftus Eye Witness testimony was done this way • How? • • • – One easy way – use redirects

Code for redirect <html> <head> <title>Image Sequence</title> <META HTTP-EQUIV="refresh" CONTENT="3; URL=page 01. 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="Bobby 0000. jpg" width="512" height="384"></p> </body> </html>

Video • You. Tube has changed internet video • Flash video (FLV) has become the default standard. • Example 1; Example 2

Flash Video • • • The format has evolved over time It is getting better and files are getting smaller Moving to an open source compression But later videos formats have less reach Create and Edit with Adobe Flash (http: //www. adobe. com/products/flash/)

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 but can be up to 30 frames/sec (and variable)

Computer Video • Effect of update rate 10 fps 15 fps 24 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 effect.

Pixel 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

Questions to Ask Yourself • Is video the only way to do this study? • How does lighting interact with the stimulus? • How do the variations in the human visual system interact with the stimulus? • If the video is interrupted how is the video degraded? • Does the increase in sample generality offset the loss of control?

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 – People may not stay – Network more likely to cause problems

Techniques • Option 1 – Buy Adobe Flash • Option 2 – Use. AVI, . MOV, . WMV, and. MPG format, whichever is convenient, and upload to You. Tube or other service • Use other format and editors – Note reduced reach and, thus, loss of participants

Editing: with Quick. Time Pro • Inexpensive addition Quick. Time Player • Basics – Opens MOV, mpg, avi, mp 3, 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

How to deliver Progressive Download Streaming • Will play when enough has been downloaded • Okay for small • Or not large number of videos • Only stream is sent, it is never whole file • Better for longer • Also for security

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

Chromatic Issues The Trichromatic Theory Color Opponent Theory Color Picker The Color Gamut Glare Color Blindness

The CIE Color System – A set of Equations that allow predictions of matching. – Used in photo printing, TV and film. – Wyszecki & Stiles (1967) – The Color Gamut • The range of colors reproducible by any system

The Effect of Illuminance on Gamut In Dark With Lights on and 30% Luminance Level

Illuminance: Example: Dark CRT LCD

Illuminance: Direct Room Light CRT LCD

One Color Study

Another Color Study Laugwitz, 2001

Illuminance • Agostini & Bruno (1996) – Accuracy of the perceived stimulus is affected by the amount of illuminance. • D. F. Neri (1990) – Combination of light and gamut changed chromaticity • Request close windows and turn off unnecessary light • Do not use subtle color differences

Color Blindness Description

Color Blindness

How to handle • Screening questions? • Large sample and random assignment • Pre-test on color blind