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Imaging Techniques in Digital Cameras Presented by Jinyun Ren Jan. 29 2004
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2 Goals Understand the basic operation of digital cameras Tell the differences between digital cameras and film cameras Study some terminologies related to digital cameras
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3 Confused Market Price( Canada $) vs. Megapixels
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4 Components Similar to 35mm film camera Including lens, aperture and shutter Already included: digital film Digital negative Digital development
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5 Digital film--Image sensor CCD or CMOS charge-couple device Complementary Metal Oxide Semiconductor Usually CCD Made of millions of photosensitive diodes photosite Each photosite captures a single pixel in final image
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6 Black and White Image sensor can only capture brightness Resulting a gray scale image Where are all colors from?
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7 What is color? RGBRGB CYMCYM
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8 Color Filter Array (CFA) between CCD and lens cover each photosite by one color in terms of certain pattern Filter out all but the chosen color for that pixel Obtain an image containing intensity values of basic colors
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9 Digital Negative--RAW Data directly from image sensor Without any in-camera process contains the full range of tone and color information captured by image sensor Camera related– You can’t change! Final image depends on how you digitally “develop” it
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10 Developing --true color True color comes from interpolation based on neighboring pixels "I'm bright green and the red and blue pixels around me are also bright so that must mean I'm really a white pixel."
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11 Developing --true color (cont) Operation demosaicing algorithm ++=
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12 Resolution Defined as X pixels times Y pixels of an image 1024X768 Equal to total pixels of CCD
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13 Resolution example Different resolution The same quality Determine the size of images Has nothing to do with image quality
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14 Image Quality On a basis of the same resolution A subjective term Good qualitypoor quality
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15 Why Compression? 24 bits color 3 bytes per pixel File size is huge without compression 1024x768=786,432 2.4M 2592x1944=5,034,960 15M Requiring to reduce file size in order to convenient operation
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16 Image compression Lossless TIFF or RAW Files remain quite large Lossy JPEG Control file size by choosing compression levels A process to degrade the image quality
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17 What is “Megapixels”? A marketing term to resolution 1-megapixel - 1024x768=786,432 2-megapixel - 1600x1200=1,920,000 3-megapixel - 2048x1536=3,145,728 4-megapixel - 2464x1632=4,021,248 5-megapixel - 2592x1944=5,034,960 Larger megapixel larger image size larger file size more storage
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18 Digital Pictures Usage Displaying on computer monitor Resolution: 1600x1200=1,920,000 Print on 6”x4” paper with top quality Resolution: 1280x960=1,228,800 Email to your friends Around 600K (after compression) daily use 2 megapixel is enough Don’t burn too much money on Megapixel!!
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19 Summary—how to choose Lens, aperture and shutter are very important Pay more attention to “digital film”, “digital negative” and “digital development methods” Don’t get confused by “Megapixel”
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20 Time is up! Q&A
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21 References http://www.shortcourses.com/choosi ng/contents.htm http://www.shortcourses.com/choosi ng/contents.htm http://www.xilinx.com/esp/dvt/cdv/c ollateral/digital_camera.pdf http://www.xilinx.com/esp/dvt/cdv/c ollateral/digital_camera.pdf http://www.dpreview.com/learn/gloss ary/ http://www.dpreview.com/learn/gloss ary/
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