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. 900kb.JPEG High Quality ~700kb
ImageJ Free at: http://rsb.info.nih.gov/ij/index.htmlhttp://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://gimp- win.sourceforge.net/stable.htmlhttp://gimp- win.sourceforge.net/stable.html
Dynamic Media Slideshows – Why – Presenting Using Redirects Video – Background – Delivering in a Webpage
Why Slideshows Example 1; Example 2 Example 1Example 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 Image Sequence Number is number of seconds before redirect This will change in 3 seconds, about
Video YouTube has changed internet video Flash video (FLV) has become the default standard. Example 1; Example 2 Example 1Example 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/)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. 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 YouTube or other service Use other format and editors – Note reduced reach and, thus, loss of participants
Editing: with QuickTime Pro Inexpensive addition QuickTime Player 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
How to deliver Progressive Download Will play when enough has been downloaded Okay for small Or not large number of videos Streaming 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 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