Post on 28-Dec-2015
How A Camera Works
Image Sensor
Shutter
Mirror
Lens
How A Camera Works
In both film and digital cameras, the image is made when the light sensitive material is exposed.
Rangefinders
Some rangefinders use a different arrangement of lens elements to capture the image
Capturing The Colors
Why?
Film and digital cameras use red, green and blue filters to help capture the image.
Color Models - Subtractive
Red, yellow and blue:The primary colors
All colors combined make black
Most are familiar with the subtractive color model:Mixing color pigments subtracts the amount of light reflected
Color Models - Additive
Red, green and blue:The primary colors
All colors combined make white
Most people use the additive color model.Mixing colors adds color light
Color Models - Color Gamut
Different color models have different gamuts: The total range of colors produced by a device.
Visible ColorsRGB
CMYK
Color Models - Color Gamut
RGB CMYK
Digital Storage - Channels
Red, green, and blue channels are used to store information about each color.
First CCD
1969-70:Bell Lab researchers Willard Boyle (left) and George Smith
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.
CMOS - The Other Sensor
Complementary metal-oxide semiconductor
Its basic function is the same as that of a CCD.
Who Can We Thank For The Technology?
He was the first to explore the photoelectric effect (won the 1921 Nobel Prize for it)
Image Sensors
Sensors called photosites used to capture light (luminance) and color (chrominance) information
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
Image Sensors
Color coatings are typically arranged in a “Bayer” pattern
Some cameras use 3 CCDs, each with a different color coating
Image Sensors
Camera must fill in the missing color information, or “interpolate” the missing pixels
Process called “demosaicing”
Getting The Picture
When light hits the surface, electrons are released and become trapped in the photosite.
Before a picture is shot, the camera charges the CCD with electrons.
Getting The Picture
The electrons in the photosite are then analyzed for content (sampled), measured for fullness and converted to bits (quantized)
1
2 8910 = 00001010
3
6
45
7
Storing The Picture
Once the image is quantized, it is stored to a card.
Storage is finite.
Compression
To make more space, compression is used.
JPEG - usually
the format used by cameras
Compression - JPEG
Short for Joint Photographic Experts Group
Uses “lossy” compression format - Details get lost
Different levels - low, medium and high
Compression - JPEG
Camera first converts image data from the original 12 or 14 bit format down to 8 bit format before compression
Compression - JPEG
Human vision is more sensitive to changes in brightness than to changes in color.
Compression - JPEG
Each pixel is expressed using a color value and a brightness value.
Color = 91e9feBrightness = 87
Compression - JPEG
8 x 8 pixels are analyzed and similar colors are grouped together and averaged.
Compression - JPEG
Too high of a compression causes artifacts