05 capture

Fundamentals of Technology

Week 5

What is Capture?

‘The Stack’

Network

Hardware

Operating System

Applications

Interface

Users

‘The Stack’

Network

Hardware

Operating System

Applications

Interface

Users

‘The Stack’

Network

Hardware

Operating System

Applications

Interface

Users

Capture

‘The Stack’

Network

Hardware

Operating System

Applications

Interface

Users

Capture

What is Capture?

-1-What is Digital Sampling?

-2-What is video?

-3-What is Color?

-4-What is Audio?

Our Heroes this Week

Our Heroes this Week

Spike Lee

Our Heroes this Week

Spike LeeGeorges Seurat

Our Heroes this Week

The CCD

Our Heroes this Week

The CCD

transducer

-1- What is Digital Sampling?

Fundamentals of Technology

Week 4

What is Information?What is Software?

Digital Audio Capture• 48 kHZ: Imagine a

snapshot of a sound wave happens 48,000 times a second.

• Plot Points are saved as digital signals and later used to re-plot the sound wave.

Digital Audio Sampling Rates8 kHZ = telephone16 kZ =VoIP32 kHz = consumer

digital video44.1 kHz = audio CD48 kHZ = professional

digital video96 kHZ = DVD audio

(surround sound)192 kHZ = DVD audio

Digital Image Capture

• The information of light per pixel becomes a digital number through ADC

• These numbers indicate:– Y Signal: Luminance

of light / dark– C signal: Chrominance

of red / green/ blue

Digital vs. Analog

• Analog devices record light and sound onto tape in ways that are ANALOGOUS to the original.

• The original could be light reflecting off of a surface (image) or movement of particles in the air (sound)

• Light and sound cause analog devices to react: silver grains in film change form, diaphragms in microphones vibrate, electrical charges move particles on a tape.

• Analog devices make copies of the light and sound that are continuous - no breaks or pauses. Infinite grains in film, infinite iron particles on audio tape.

Digital vs. Analog

• Digital devices record light and sound by sampling the original (breaking it into discrete packets or values).

• Sampling takes place at X times / second (area).• More samples = higher resolution (quality)• More pixels per image (to a point) = higher quality • Too many pixels can create “noise”• Fewer samples = lower resolution• Resolution ≠ Quality

– best resolution depends on use!

Digital AnalogDuplication of data without loss of quality

Wear of tapes, Bleed through, Generation Loss

Cheaper, more portable devices

Larger, heavier, more expensive devices

Distortion and Drop OutNo Drop Out,

Peaks can be controlled

Sampling (makes a circle or wave into a square)

Continuous copy (preserves circle/wave)

Compressed information easy to share/transport

Requires original tapeand equipment

-2- What is Video?

Video Basics: From Light . . .

to Digital Camera . . .. . . to Image

How do Lenses Work?

How do Lenses Work?Iris / Aperture / F-Stops

• Focal Length = Distance from lens to its

focal point (CCD Chip)

• F-stop is the focal length divided by the diameter of the lens (iris).

• Each F-Stop reduces or increases the amount of light by two (x 2 or ½)

How do Lenses Work?

Types of Lenses

Wide Angle Lens– Focal Length: 10 mm, 12 mm

Medium Lens– Focal Length: 25 mm – 50 mm

Telephoto Lens– Focal Length: 100 mm

Shutter

ShutterFor video, think of the shutter as a rotating half disc placed in front of the aperture.

- every pass interrupts the flow of light- every interruption marks a new frame

Shutter speed = How many times does the shutter rotate per second?

ShutterFor video, think of the shutter as a rotating half disc placed in front of the aperture.

- every pass interrupts the flow of light- every interruption marks a new frame

Shutter speed = How many times does the shutter rotate per second?

- Video = 30 frames per second- the Disc needs to rotate twice for each frame

of video, so the standard shutter speed for 30fps video is 60.

Controlling LightAdd Light(interior / dark situation)

Reduce Light (sunlight, exteriors, very bright situation)

Open iris = lower F-stop Close iris = raise F-stop

Increase the Gain - adds white noise (+dB)

Lower Gain/Add Filter adds black noise (-dB)

Reduce shutter speed Increase shutter speed

Flow of Digital Video • Light to Beam Splitter

• Beam Splitter to CCD

• CCD to Digital Signal (C and Y)

• Digital Signal to Output

• Digital Input to Video Image.

The Beam Splitter• White light enters the lens

and a splitter separates light into three colors: Red, Blue and Green.

• Prism block directs these color streams to an imaging device called a CCD.

CCD: Charge Coupled Device• The CCD is perhaps the

most important element determining the ‘quality’of a digital image.

• The CCD translates light into an electrical signal.

• A one chip camera does not separate Red/Green/ Blue. A three chip camera does (one chip per color).

CCD: Charge Coupled Device• The CCD is comprised of

rows and rows of light and color sensitive pixels.

• Pixels sense how much light is present.

• The CCD records: – Y Signal: Luminance

of light / dark– C signal: Chrominance

of red / green/ blue

Recording onto the Tape

From Tape to Television• Television uses interlaced

scanning: every other scan fills in an “even” or “odd” line

• Every scan takes 1/60th of a second so 1 full frame (= two lines) is scanned every 1/30th of a second

• Video frame rate is 30 fps

Types of Connectors

Component

Types of Connectors

Composite

Component

Types of Connectors

Composite

Component

Types of Connectors

Composite

Component

-3- What is Color?

The Beam Splitter

• White light enters the lens and a splitter separates light into three colors: Red, Blue and Green.

• Prism block directs these color streams to an imaging device called a CCD.

Color mixing: additive RGB

Color Temperature

Color Temperature• Exterior light - 5400K BLUE• Interior (tungsten lights) - 3200 K ORANGE• Fluorescent - green• Sunset exterior - blue/orange• Mid day sun exterior - bright blue

Color Temperature Variations

-4-Spike Lee

Color mixing: additive RGB

Georges Seurat: Parade de Cirque

oil on canvas, 1884–86

Artifact: Moiré Effect

Color mixing: additive RGB

Color mixing: subtractive CMYK

-4- What is Audio?

How Does Sound Work?

• An object vibrates• Molecules in the air move• Move the molecules next to them• Start a sound wave

• At Sea Level: 340.29 m/s (761 mph)

Frequency and Amplitude

Frequency: Repetition of event (how many)* Frequency of a sound wave is Pitch *

– low frequency, low pitch– high frequency, high pitch

Amplitude: Magnitude of oscillation (how much)* Amplitude of a sound wave is Volume *

– low amplitude, low volume– high volume, high volume

How Microphones Work

Transducer: Converts molecular Converts molecular disturbances into electrical energy.disturbances into electrical energy.

* * Roughly equivalentRoughly equivalentthe the CCD chipthe the CCD chipof the camera.of the camera.

Dynamic Microphone• Magnet and coil of

wire converts sound waves into electrical energy.

• Extremely ruggedExtremely rugged

Condenser Microphone• Two plates with Two plates with

voltage between voltage between them. them.

• One plate acts like a One plate acts like a diaphragm: when it diaphragm: when it vibrates it changes vibrates it changes the voltage.the voltage.

Condenser Microphone• Can be very small - Can be very small -

lavaliere microphoneslavaliere microphones• Sensitive to high and Sensitive to high and

low frequency soundslow frequency sounds

• Output signal is weak! Output signal is weak! *requires amplification*requires amplification from an external source from an external source

Microphone Directionality

Omnidirectional Unidirectional

Microphone Directionality

Types of Connectors

Balanced

Types of Connectors

Unbalanced

Balanced

Types of Connectors

Unbalanced

Balanced

Signal or Noise?

Types of Connectors

Unbalanced

Balanced

Audio Recording Choices

• Analog or digital? Sampling rate?• Type of microphone:

Dynamic or condenser?• Pickup pattern for microphone?• Mono or stereo channels (or

more)? • What cables connect the devices?