1.2 Multimedia

Bitmap Images

• Pixel: Smallest picture element whose color can be accurately represented by binary
• Data for a bitmapped image is encoded by assigning a solid color to each pixel, i.e., through bit patterns.
• Bit patterns are generated by considering each grid row as a series of binary color codes corresponding to each pixel’s color.
• These bit patterns are ‘mapped’ onto the main memory.
• File Header: Stores the metadata of bitmap file; image size, color depth
• Image Resolution
  • Number of pixels in an image
  • Image Resolution = width × height; E.g. 1920 × 1080 pixels
  • Image resolution increases → sharper/more detailed image
• Screen Resolution
  • Number of pixels which can be viewed horizontally & vertically on the device’s screen
  • Number of pixels = width × height; E.g. 1680 × 1080 pixels
• Color depth: Number of bits used to represent each color
  • An image with n bits has 2n colors per pixel
  • E.g. 16-color bitmap has 4 bits per pixel ∵ 24 = 16
  • Increased Color Depth → Increased Color Quality → Increased Size
• File Size = Number of Pixels (Image Resolution) × Colour depth
• Formats:
  • JPEG (.jpg or .jpeg) - Compressed format with lossy quality
  • PNG (.png) - Lossless format supporting transparency
  • GIF (.gif), BMP (.bmp), PSD (.psd), HEIF (.heic or .heif), ICO (.ico)
• Applications: Scanned images and general computer usage

Vector Graphics

• Made up of drawing objects
• Drawing objects: A mathematically defined construct (of shapes like rectangle, line, circle, etc.)
• Drawing List: Set of commands defining the vector
• Properties: Basic geometric data which determine the shape and appearance (e.g color, stroke).
• Data is encoded using mathematical formulas to generate properties in order to draw lines & curves to create the image
• If object is resized, properties are recalculated
• Applications: Logos and Icons
• Formats:
  • SVG (.svg) - Scalable Vector Graphics: Widely-used web standard format supporting interactivity and animation.
  • EPS (.eps)
  • PDF (.pdf) – Portable Document Format
  • AI (.ai) – Adobe Illustrator format

Sound

• Analogue data is continuous electrical signals whereas digital data is discrete electrical signals.
• Sound signals are vibrations through a medium. Hence are analogue in nature as there can be infinite detail for sound.
• Analogue signals converted (encoded) to digital signals by sampling:
  • Sound wave’s amplitude sampled at set time intervals
  • These samples are encoded as a binary number sequence
  • This provides a digital representation of the sound wave
• Sampling Rate
  • Number of samples taken in a second
  • Unit: Hertz (Hz)
  • ↑ Sampling Rate = ↑ Accuracy = ↑ File size.7
• Sampling Resolution
  • Number of bits per sample
  • ↑ Sampling Resolution = ↑ Accuracy = ↑ File size
• Bit Rate
  • Number of bits for storing 1 second of sound
  • Bit Rate = Sampling Rate x Sampling Resolution
• File Size = Bitrate x Length of Sound
  For Stereo sound (sound with two channels) file, multiply results by two
• File Formats:
  • Musical Instrument Digital Format - MIDI (.mid): Stores musical performance data, such as notes, timings, and control signals, without including actual audio, allowing instruments or software to reproduce the composition
  • WAV (.wav), FLAC (.flac) - Uncompressed, High-quality
  • MP3 (.mp3) - Compressed format with lossy audio quality