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

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)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