- Problem
- World HDR
- 8 or more orders of maginitude (1 with 8 zeros after)
(sun, lights, moon,stars)
- 6 or more in a given scene often
- Human visual system
- 5 orders magnitude in scene
- 10 with adaptation
- Film -- about 3 orders of magnitude basic
- Digital-- 256 levels standard
- paper,slide show, monitor about 2 orders of magnitude
- Solutions:
- Live with it
- Cheat the eye into thinking more range in paper, monitor
etc than you have. To do this you have to
know/capture the high range to work with. May mean needing
more accuracy than 256 levels too.
- nerves are typically center surround so if have light
surrounded by dark light will look brighter.
- artists use this artistically
- Tone mapping with film: eg. zone system of Ansel
Adams(look under images in google search)-film higher
dynamic range than paper
- expose for darks, develop for the bright is a form
of global tone mapping that just remaps range into
negative density
- burning and dodging give local tone operator
- just digitally compress bigger range into 256
range of digital work - lose contrast
- Digital
- Take many pictures at different exposure levels
- Combine them into a format that can express all the full
dynamic range without posterizing
- demo posterizing with Veal
- The gray scale is most important
- edit --> convert to profile--- put in Lab
space
- Color balance Green-- Magenta is the a channel
and blue--yellow is the b channel
- In channels blur Lightness, a and b
- we see lightness dominates for accuity
- posterizing messes up color in channels but not
accuity
- Now have artist problem of tone mapping
- Why do we care:
- more interesting images
- Hollywood -- initially get people back to theaters
- security -- no hiding
- games
- art
- more manipulative possibilities with images
- lighting (later)
- How do we aquire images:
- scan negative several times-- trouble
- take pictures at several exposures
- not great if subject moves
- new cameras and chips