How A Camera Works

1. How A Camera Works Image Sensor Shutter Mirror Lens

2. How A Camera Works In both film and digital cameras, the image is made when the light sensitive material is exposed.

3. Rangefinders Some rangefinders use a different arrangement of lens elements to capture the image

4. Capturing The Colors Film and digital cameras use red, green and blue filters to help capture the image. Why?

5. Color Models - Subtractive Most are familiar with the subtractive color model:Mixing color pigments subtracts the amount of light reflected Red, yellow and blue:The primary colors All colors combined make black

6. Color Models - Additive Most people use the additive color model.Mixing colors adds color light Red, green and blue:The primary colors All colors combined make white

7. Color Models - Color Gamut Different color models have different gamuts: The total range of colors produced by a device. Visible Colors RGB CMYK

8. Color Models - Color Gamut RGB CMYK

9. Digital Storage - Channels Red, green, and blue channels are used to store information about each color.

10. First CCD 1969-70: Bell Lab researchers Willard Boyle (left) and George Smith

11. CCD? No It’s Not Catechism Charge Coupled Device: one of the two main types of image sensors used in digital cameras. Contain hundreds of thousands of photo-sites that convert light energy into electronic signals.

12. CMOS - The Other Sensor Complementary metal-oxide semiconductor Its basic function is the same as that of a CCD.

13. Who Can We Thank For The Technology? He was the first to explore the photoelectric effect (won the 1921 Nobel Prize for it)

14. Image Sensors Sensors called photosites used to capture light (luminance) and color (chrominance) information

15. Image Sensors Photosites are typically coated with red, green and blue filters to separate red green and blue light Canon uses CYGM filters, Sony uses RGB and emerald

16. Image Sensors Color coatings are typically arranged in a “Bayer” pattern Some cameras use 3 CCDs, each with a different color coating

17. Image Sensors Camera must fill in the missing color information, or “interpolate” the missing pixels Process called “demosaicing”

18. Getting The Picture Before a picture is shot, the camera charges the CCD with electrons. When light hits the surface, electrons are released and become trapped in the photosite.

19. Getting The Picture 1 7 9 2 10 = 00001010 8 The electrons in the photosite are then analyzed for content (sampled), measured for fullness and converted to bits (quantized) 3 4 5 6

20. Storing The Picture Once the image is quantized, it is stored to a card. Storage is finite.

21. Compression To make more space, compression is used. JPEG - usually the format used by cameras

22. Compression - JPEG Short for Joint Photographic Experts Group Uses “lossy” compression format - Details get lost Different levels - low, medium and high

23. Compression - JPEG Camera first converts image data from the original 12 or 14 bit format down to 8 bit format before compression

24. Compression - JPEG Human vision is more sensitive to changes in brightness than to changes in color.

25. Compression - JPEG Each pixel is expressed using a color value and a brightness value. Color = 91e9feBrightness = 87

26. Compression - JPEG 8 x 8 pixels are analyzed and similar colors are grouped together and averaged.

27. Compression - JPEG Too high of a compression causes artifacts