Multimedia: Sound and Graphics
1. Graphics: Capturing the Visual World
The Digital Camera Process
- Light passes through the lens onto a sensor (usually a CCD or CMOS).
- The sensor is made of a grid of millions of light-sensitive cells (photosites).
- Each cell measures the intensity of light and converts it into an Analogue Voltage.
- An ADC (Analogue to Digital Converter) converts these voltages into binary values.
- The software assigns a color value based on the binary data and stores it as a grid of Pixels.
Factors Affecting Graphic Quality
Hardware
Sensor Resolution (Megapixels)
More megapixels mean smaller, denser pixels, allowing for finer detail and larger prints without "pixelation."
Data
Color Depth (Bit Depth)
The number of bits used per pixel. 24-bit depth allows for 16.7 million colors, creating smoother gradients.
Realistic Example: A "Budget" smartphone and a DSLR might both have 12MP. However, the DSLR has a larger physical sensor size, allowing it to capture more light with less "noise" in dark environments.
2. Sound: Capturing the Acoustic World
The Digital Sound Process
- Sound waves (vibrations in the air) hit the diaphragm of a microphone.
- The microphone converts these vibrations into a continuous Analogue Electrical Signal.
- The computer "Samples" the amplitude (height) of the wave at regular intervals.
- The ADC converts each sample amplitude into a binary number.
- The resulting stream of binary numbers is stored as a digital audio file (e.g., WAV or MP3).
Factors Affecting Sound Quality
Data
Sampling Rate (Hz)
The number of samples taken per second. Standard CD quality is 44.1 kHz (44,100 samples per second).
Data
Sampling Resolution (Bit Depth)
The number of bits used to store each sample. 16-bit sound provides 65,536 distinct volume levels, reducing "quantization error."
Realistic Example: Recording a lecture on a phone (low sample rate) vs. recording a violin concerto in a studio (high sample rate). The violin recording needs a high sample rate to capture high-frequency harmonics that the phone would "miss," resulting in a flat, dull sound.
⚠️ AS-Level Note: The Nyquist Theorem
For accurate digital representation, the Sampling Rate must be at least twice the highest frequency of the sound being recorded. Since humans hear up to 20kHz, we sample at ~44kHz.