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