Teaching:TUW - UE InfoVis WS 2008/09 - Gruppe 05 - Aufgabe 1 - Mach band: Difference between revisions
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===DEFINITION=== | ===DEFINITION=== | ||
{{Quotation| Mach bands are an optical illusion consisting of an image of two wide bands, one | {{Quotation| Mach bands are an optical illusion consisting of an image of two wide bands, one light and one dark, separated by a narrow strip with a light-to-dark gradient. The human eye perceives two narrow bands of different brightnesses either side of the gradient that are not present in the original image. The illusion is named after Ernst Mach. |[Wikipedia]}} | ||
light and one dark, separated by a narrow strip with a light-to-dark gradient. The | |||
human eye perceives two narrow bands of different brightnesses either side of the | |||
gradient that are not present in the original image. The illusion is named after Ernst | |||
Mach. |[Wikipedia]}} | |||
---- | ---- | ||
===CAUSATION=== | |||
The mach band effect is supposed to be caused by lateral inhibition. Imagine three neighbouring | |||
retina receptor cells - each one of them is stimulated at a different light-intensity level. The level of the | |||
stimulation is transformed into action potentials and later on forwarded to its | |||
neighbours. Inhibitory interneurons weaken these signals and transfer them to so | |||
called secondary neurons. The attenuation is proportional to the excitation of the | |||
interneurons. By the summation of exciting and alleviative factors to the second | |||
neuron a contrast enhancement is archieved. | |||
As shown in the image below, we have to examine the edge which is represented schematically between an | |||
homogenous bright area (between receptor 1 and 5) and an homogenous dark area | |||
(between receptor 6 and 10). Without interaction every receptor of 1 to 5 would | |||
represent the same high and every receptor from 6-10 the same low signal. But | |||
because of the connection by an horizontal receptor cell the signal of for example receptor 3 is | |||
attenuated because his neighbours impact on it inhibitorily. Only 5 and 6 are not | |||
affected because the have the same amount of inhibitory and excitatory neighbours. | |||
[[Image:Machband.JPG]] | |||
===EXAMPLES=== | ===EXAMPLES=== | ||
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[[Image:w2lg_stripes_15.gif]] | [[Image:w2lg_stripes_15.gif]] | ||
===Machband and Rendering=== | ===Machband and Rendering=== | ||
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Phong Shading. | Phong Shading. | ||
===LINKS=== | |||
[Mach Banding Interactive Demonstration] http://www.nbb.cornell.edu/neurobio/land/OldStudentProjects/cs490-96to97/anson/MachBandingApplet/ | |||
===REFERENCES=== | ===REFERENCES=== | ||
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[Wikipedia] http://de.wikipedia.org/wiki/Laterale_Hemmung | [Wikipedia] http://de.wikipedia.org/wiki/Laterale_Hemmung | ||
[Wikipedia] http://en.wikipedia.org/wiki/Mach_bands | |||
[Perceptual Stuff] http://perceptualstuff.org/machbandsbasic.html | [Perceptual Stuff] http://perceptualstuff.org/machbandsbasic.html | ||
Revision as of 18:42, 22 November 2008
Mach Band
DEFINITION
CAUSATION
The mach band effect is supposed to be caused by lateral inhibition. Imagine three neighbouring retina receptor cells - each one of them is stimulated at a different light-intensity level. The level of the stimulation is transformed into action potentials and later on forwarded to its neighbours. Inhibitory interneurons weaken these signals and transfer them to so called secondary neurons. The attenuation is proportional to the excitation of the interneurons. By the summation of exciting and alleviative factors to the second neuron a contrast enhancement is archieved.
As shown in the image below, we have to examine the edge which is represented schematically between an homogenous bright area (between receptor 1 and 5) and an homogenous dark area (between receptor 6 and 10). Without interaction every receptor of 1 to 5 would represent the same high and every receptor from 6-10 the same low signal. But because of the connection by an horizontal receptor cell the signal of for example receptor 3 is attenuated because his neighbours impact on it inhibitorily. Only 5 and 6 are not affected because the have the same amount of inhibitory and excitatory neighbours.
EXAMPLES
Try to differ as many colors as possible
White to black in 10 Steps
White to grey (255,255,255 -> 200,200,200) in 20 Steps
White to a lighter grey(220) in 20 steps (you can see the difference? – probably)
Same as above but with seperators (Can you see a difference in the middle
part?)
Machband and Rendering
Due to the linear intensity interpolation the Mach bands can cause trouble when for example using Gouraud Shading for rendering. Here the Machband effect can be visible at the edges of polygons. A rendering method which can work around the mach-band is Phong Shading.
LINKS
[Mach Banding Interactive Demonstration] http://www.nbb.cornell.edu/neurobio/land/OldStudentProjects/cs490-96to97/anson/MachBandingApplet/
REFERENCES
[Schmitt, Sturm, Pries, 2006] Lutz Pries, Frank Schmitt, Patrick Sturm. Fragmente eines Skripts zur Bildverarbeitung. 31. Oktober 2006, http://www.uni-koblenz.de/~lb/lehre/ws2006/bv/bvbuch.pdf
[Biokurs.de] Lichtsinn. http://www.biokurs.de/skripten/12/bs12-38b.htm
[Wikipedia] http://de.wikipedia.org/wiki/Laterale_Hemmung
[Wikipedia] http://en.wikipedia.org/wiki/Mach_bands
[Perceptual Stuff] http://perceptualstuff.org/machbandsbasic.html
[The Joy of Visual Perception] http://www.yorku.ca/eye/machband.htm
[Mach Banding Interactive Demonstration] http://www.nbb.cornell.edu/neurobio/land/OldStudentProjects/cs490-96to97/anson/MachBandingApplet/