1 / 17

Digital Image processing

Digital Image processing. CMSC 150: Lecture 14. Conventional Cameras. Entirely chemical and mechanical processes Film: records a chemical record of light pattern Light-sensitive grains in chemical suspension on plastic Upon light exposure, grains undergo reaction

rooney-howell
Download Presentation

Digital Image processing

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Digital Image processing CMSC 150: Lecture 14

  2. Conventional Cameras • Entirely chemical and mechanical processes • Film: records a chemical record of light pattern • Light-sensitive grains in chemical suspension on plastic • Upon light exposure, grains undergo reaction • Development: expose film to other chemicals • Chemicals dye the layers of red, green, blue • Overlay to get full-color negative

  3. Conventional Cameras

  4. Digital Cameras • Sensor converts light to electrical charges • 2D array of many tiny cells • Light hits, converted into electrons • Charge is converted into binary form CCD: Charge Coupled Device

  5. Analog to Digital Conversion: Sampling

  6. Analog to Digital Conversion: Sampling

  7. Analog to Digital Conversion: Sampling

  8. Analog to Digital Conversion: Sampling

  9. Analog to Digital Conversion: Sampling

  10. Digital Image • Sensor: 2D array of values • Image: "value" stored for cell in the sensor • Pixel: picture element • One pixel per sensor cell

  11. Capturing Color • Color filter placed over sensor • Color at each cell determined as "average of neighbor cells" (How Stuff Works animation)

  12. Grayscale vs. Color • Grayscale: pixel corresponds to shade of gray • Highest value: white • Lowest value: black

  13. Grayscale Images: Example • PGM: Portable Graymap • Use 8-bits per pixel • 256 total graylevels, 0-255 • Each pixel represented by an integer • 0: black • 255: white • Let's play around with a few, using IrfanView

  14. Grayscale vs. Color • Color: pixel corresponds to three color intensities • Red, Green, Blue • In general, color image at least 3X footprint of grayscale

  15. RGB: Additive Color Model • Start from no color present (black background) • Add (emit) amounts of each primary • Full intensity of each R,G,B: white • Full intensity of R,G: yellow

  16. Resolution • Image quality vs. number of pixels • Each image below stretched to 200x200 pixels • Fewer pixels less information stored 25x25 original 625 pixels 50x50 original 2500 pixels 100x100 original 10000 pixels

  17. Image Quality Vs. Color Levels • Clockwise on right: • 2 levels per R,G,B • 4 levels per R,G,B • 10 levels per R,G,B • 40 levels per R,G,B • More bits per pixel •  more colors •  larger footprint •  better quality

More Related