Multimedia – Graphics, Sound (Copy)

Bit-map Images

• Made of pixels
  • Picture Elements
• Image is stored in two-dimensional matrix of pixels
• Consideration
  • At least 1 byte per pixel required for colored image
    • Gives 256 different combinations
    • Based on color intensity of green, red and blue
  • Ture color needs 3 bytes per pixel
    • 24 bits
    • 1 million color options per pixel
  • Color Depth
    • Number of bits per pixel
• Bit Depth
  • The number of bits used per pixel
  • A bit depth of 8 bits per pixel allows a color depth of 2^8 i.e. 256 color depth per pixel
• Image Resolution
  • Number of pixels making up an image
    • For example 1024*780
• Screen Resolution
  • Number of horizontal pixels and vertical pixels on the screen display
  • If screen resolution is smaller than image resolution
    • The entire image can not be shown
    • Lower quality image
  • If the picture is zoom or enlarged, it will get pixelated
    • Pixelated = less pixels per square inch (pixel density)
      • It will reduce the image quality.
• Pixel density calculation
  • First add the square of the resolution sizes
  • Find the square root
  • Divide by screen size in inches
• Pixel generated image can be scaled.
  • It can be done when deciding resolution
• Bitmap Image File Size
  • We need image resolution and bit depth
  • We multiply the image resolution with bit depth
  • It gives the total number of bits required for the complete image
  • Divide it by 8 to convert it into bytes.
  • An image not taking the full screen will be of smaller file size as well.

Vector Graphics

• 2D points are used to decide lines and curves, that will help in determining the properties of geometric shapes
• CAD can be used to design them
• Vector graphic file contains drawing list
  • Command used for each object
  • Attributes defined for properties
  • Relative position of each object
  • Dimensions not provided instead relative positions provided.

Differences

• Bitmap
  • Tiny pixels different colors
  • Edit pixels to change design
  • File size large
  • Very realistic
  • Jpeg, bmp, png format
  • More realistic than vector
• Vector
  • Many geometric shapes make it up
  • Change geometric shapes to change design
  • File size small
  • Not very realistic
  • svg, cgm and odg format
  • Better for resizing
  • Scale drawing best option

Sound Files

• Sound needs medium to travel
• Not travel in vacuum
• Oscillation of particles creates medium
• Frequency, Wavelength and Loudness
• Sound is analogue
• Computer only understands digital
• Analogue to digital converter (ADC) used to convert it into music files
• Filtered to remove frequencies higher or lower than human hearing capabilities.
• Sound waves sampled at a given time rate
  • Amplitude can not be measured precisely
    • Only approximately
• X axis on the sound wave shows tie intervals of sound sampling
• E axis shows the amplitude
• Sampling Resolution (Bit Depth)
  • Number of bits used to represent sound amplitude
  • It increases the sampling accuracy of the sound if sampling resolution increased
• Sampling Rate
  • Number of sound samples taken every second
• Both higher sampling rate or resolution will increase file size.
• Method of sampling
  • Amplitude of the sound is determined at set intervals (sampling rate)
  • Approximate representation is given to sound wave
  • Sound wave is encoded as series of binary digits.
• Higher sampling rate or larger resolution provides more realistic representation of the actual sound
• Higher sampling resolution
  • Benefits
    • Larger dynamic range
    • Better sound quality
    • Less sound distortion
  • Cons
    • Larger file size
    • Transmission time is long
    • Greater processing power required
• Sounds can be edited with a software