MITMAS_531F09_lec10_notes - MAS.531: Computational Camera...

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Unformatted text preview: MAS.531: Computational Camera and Photography Fall 2009 Animal Eyes Prof. Ramesh Raskar November 13, 2008 Lecture 9 This is a guest lecture by Quinn Smithwick based on the book Animal Eyes [1]. Section titles roughly match slide titles. We use to indicate reference to application in modern technology. Eye Function The fundamental purpose of the eye is to compare intensity of light coming from different directions. Hence, two characteristics are of importance: directional resolution comes from optics and photoreceptor density sensitivity ability to collect light, contrast (dynamic range) Both are optimized for the environment, task, size, available computational power. For instance, a small y has a tiny brain and need to navigate. In contrast, a big whale in the depth of oceans needs to collect the little light there is. We can distinguish different kinds of requirements: diurnal (day+night) vs. nocturnal at vs. 3-d vision prey vs. predator slow vs. high speed Thus, high directional resolution is not always needed or available. On the other hand, sensitivity might not be an issue if in bright light. Well see how different animal eyes evolved to match their environment. And remem- ber, animal build the eyes from the stuff they eat. Also, animals dont always depend on light/vision, there are many other senses often better in the environment. Rhodopsin Rhodopsin is the protein in photoreceptor. Its a light sensitive molecule that is actually a combination of retinal and opsin . Inactivated its all folded up, but when struck by light 9-1 it unfolds and releases the opsin. This triggers a signal transduction cascade and electrical impulse in bipolar cells (a type of sensory neurons specialized for transmission of special senses). Retinal is also known as vitamin A , so it makes sense when moms tell their children to eat carrots for better sight. Different opsin molecules absorb different wavelengths, lead- ing to color vision using cones . Ratios of responses to wavelengths determine the perceived color. Cryptochromes are special blue light photoreceptors that allow birds to see magnetic fields! Struck by blue light the protein separates. The more magnetic field the longer it stays active, hence it is less sensitive to incoming light. I.e., the more magnetic field present, the darker the vision. This way, birds can orient themselves with the magnetic field. One downside: its superoxide- very toxic- so its okay for birds, as they dont live long, but might be unhealthy for humans. Preferential orientation of rhodopsin leads to polarization sensitive vision. In human eyes, they are stored in disc, no specific orientation, were equally sensitive to all polarizations....
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MITMAS_531F09_lec10_notes - MAS.531: Computational Camera...

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