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Exploring Digital Cameras: Effects & Techniques

Discover the evolution of digital cameras, from pinhole to high dynamic range imaging, exploring lenses, aperture, shutter speed, color processes, and sensor technologies. Learn about effects like distortion, depth of field, noise, and color filtering. Dive into the world of visual effects with this insightful guide.

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Exploring Digital Cameras: Effects & Techniques

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  1. Cameras Digital Visual Effects, Spring 2005 Yung-Yu Chuang 2005/3/2 with slides by Brian Curless, Steve Seitz and Alexei Efros

  2. Announcements • Classroom is changed to Room101 • Assignment schedule • Image morphing (3/9-3/30) • Image stitching (3/30-4/20) • Matchmove (4/20-5/11) • Final project (5/11-6/22) • Scribe • Send cyy@csie.ntu.edu.tw to subscribe vfx

  3. Outline • Pinhole camera • Film camera • Digital camera • Video camera • High dynamic range imaging

  4. Camera trial #1 film scene Put a piece of film in front of an object.

  5. barrier Pinhole camera pinhole camera film scene Add a barrier to block off most of the rays. • It reduces blurring • The pinhole is known as the aperture • The image is inverted

  6. Shrinking the aperture Why not make the aperture as small as possible? • Less light gets through • Diffraction effect

  7. Shrinking the aperture

  8. Camera Obscura Drawing from “The Great Art of Light and Shadow “ Jesuit Athanasius Kircher, 1646.

  9. High-end commercial pinhole cameras http://www.bobrigby.com/html/pinhole.html

  10. Adding a lens

  11. “circle of confusion” Adding a lens lens film scene A lens focuses light onto the film • There is a specific distance at which objects are “in focus” • other points project to a “circle of confusion” in the image

  12. Lenses • Any object point satisfying this equation is in focus • Thin lens applet: http://www.phy.ntnu.edu.tw/java/Lens/lens_e.html Thin lens equation:

  13. Exposure = aperture + shutter speed • Aperture of diameter D restricts the range of rays (aperture may be on either side of the lens) • Shutter speed is the amount of light is allowed to pass through the aperture F

  14. Aperture • Aperture is usually specified by f-stop, f/D. When a change in f-stop occurs, the light is either doubled or cut in half. • Lower f-stop, more light (larger lens opening) • Higher f-stop, less light (smaller lens opening)

  15. Depth of field Changing the aperture size affects depth of field. A smaller aperture increases the range in which the object is approximately in focus See http://www.photonhead.com/simcam/

  16. Distortion • Radial distortion of the image • Caused by imperfect lenses • Deviations are most noticeable for rays that pass through the edge of the lens No distortion Pin cushion Barrel

  17. Correcting radial distortion from Helmut Dersch

  18. Film camera aperture & shutter lens & motor film scene

  19. Digital camera aperture & shutter • A digital camera replaces film with a sensor array • Each cell in the array is a light-sensitive diode that converts photons to electrons sensor array lens & motor scene

  20. CCD v.s. CMOS • CCD is less susceptible to noise (special process, higher fill factor) • CMOS is more flexible, less expensive (standard process), less power consumption CCD CMOS

  21. Sensor noise • Blooming • Diffusion • Dark current • Photon shot noise • Amplifier readout noise

  22. Color So far, we’ve only talked about monochrome sensors. Color imaging has been implemented in a number of ways: • Field sequential • Multi-chip • Color filter array • X3 sensor

  23. Field sequential

  24. Field sequential

  25. Field sequential

  26. Lantern projector Prokudin-Gorskii (early 1990’s) http://www.loc.gov/exhibits/empire/

  27. Prokudin-Gorskii (early 1990’s)

  28. wavelength dependent Multi-chip

  29. Embedded color filters Color filters can be manufactured directly onto the photodetectors.

  30. Kodak DCS620x Color filter array Color filter arrays (CFAs)/color filter mosaics

  31. Bayer pattern Color filter array Color filter arrays (CFAs)/color filter mosaics

  32. Bayer’s pattern

  33. original input linear interpolation Demosaicking CFA’s bilinear interpolation

  34. Demosaicking CFA’s Constant hue-based interpolation (Cok) Hue: Interpolate G first

  35. Demosaicking CFA’s Median-based interpolation (Freeman) 1. Linear interpolation 2. Median filter on color differences

  36. original input color difference median filter reconstruction Demosaicking CFA’s Median-based interpolation (Freeman) linear interpolation

  37. Demosaicking CFA’s Gradient-based interpolation (LaRoche-Prescott) 1. Interpolation on G

  38. Demosaicking CFA’s Gradient-based interpolation (LaRoche-Prescott) 2. Interpolation of color differences

  39. Demosaicking CFA’s bilinear Cok Freeman LaRoche

  40. Demosaicking CFA’s Generally, Freeman’s is the best, especially for natural images.

  41. Foveon X3 sensor • light penetrates to different depths for different wavelengths • multilayer CMOS sensor gets 3 different spectral sensitivities

  42. Foveon X3 sensor Bayer CFA X3 sensor

  43. Color processing • After color values are recorded, more color processing usually happens: • White balance • Non-linearity to approximate film response or match TV monitor gamma

  44. White Balance warmer +3 automatic white balance

  45. Manual white balance white balance with the white book white balance with the red book

  46. Autofocus • Active • Sonar • Infrared • Passive

  47. Digital camera review website • http://www.dpreview.com/

  48. Camcorder

  49. Interlacing without interlacing with interlacing

  50. deinterlacing weave blend

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