Color Models and Quantization Quiz

Quantizing the Image

• 1 bit allows for 2 colors (2¹ = 2), typically black and white.
• 2 bits allow for 4 colors (2² = 4).
• 4 bits allow for 16 shades.
• 8 bits allow for 256 shades.
• More bits lead to more shades of gray.

Subtractive Model - CMYK

• Used in printing.
• Ink is applied to paper.
• Primary colors are cyan, magenta, and yellow.
• Ink subtracts light from white, creating different colors.

Additive Model - RGB

• Used on monitors.
• Light is emitted from a black background.
• Primary colors are red, green, and blue.
• Light is added to create different colors.

Representing Colors on a Monitor

• True Color:
  • Represents 2²⁴ colors (approximately 16 million).
  • Requires 3 bytes per pixel (8 bits each for red, green, and blue).
  • Can be encoded using decimal numbers (0-255) or hexadecimal codes (#RRGGBB).

Encoding True Colors

• Decimal:
  • 0 represents no amount of color.
  • 255 represents the maximum amount of color.
• Hexadecimal:
  • #RRGGBB: RR, GG, and BB represent the amount of red, green, and blue respectively.
  • 00 in hex corresponds to 0 in decimal.
  • FF in hex corresponds to 255 in decimal.
  • Examples:
    • #000000 (black)
    • #090807 (dark gray)
    • #0A0F09 (dark green)
    • #FF00FF (magenta)
    • #420063 (purple)

Indexed Color Images

• Used when 16 million colors are unnecessary.
• An index maps to a specific set of colors used.
• Example: Clip art and cartoon images.
• Indexed color depth is typically 8 bits, allowing for 256 colors (2⁸).
• Each pixel refers to a color from the index, saving space.
• Provides a good visual quality despite a limited color palette.

Bitmapped vs Vector Graphic Images

Bitmapped Graphic Image

• Made up of pixels arranged in a grid.
• Examples: Icons, photographs.
• Resolution dependent:
  • Images appear larger on lower resolution screens.
  • Images become distorted when enlarged.
• File size increases when images are enlarged.
• Common file formats: BMP, GIF, JPEG, JPG, PNG, PICT, PCX, TIFF.

Vector Graphic Image

• Made up of scalable objects defined by mathematical equations.
• Objects consist of lines, curves, and shapes.
• No distortion when enlarged.
• Crisp, clean lines even at large sizes.
• Usually have smaller file sizes than bitmapped images.
• Ideal for logos and drawings.

Image File Size

• Calculated as: Total pixels x Color Bit Depth (in bytes).
• Formula: (Length in pixels) x (Width in pixels) x (Color Bit Depth in bytes).
• Example:
  • 1600 pixels x 1200 pixels x 3 bytes/pixel = 5,760,000 bytes.
  • 5,760,000 bytes / 1024 = 5625 kilobytes.
  • 5625 kilobytes / 1024 = 5.5 megabytes.

Units of Measure

• 1 kilobyte (kb) = 1024 bytes (B).
• 1 megabyte (Mb) = 1024 kilobytes (KB).
• 1 gigabyte (Gb) = 1024 megabytes (MB).
• 1 terabyte (TB) = 1024 gigabytes (GB).

Compressing File Size

• Option 1: Reducing the physical size of the image, but this affects the displayed size.
  • Example: 100 pixel by 100 pixel image (30kb) is smaller than a 200 pixel by 200 pixel image (118kb).
• Option 2: Compressing the image file using techniques to reduce file size without sacrificing quality or pixel dimensions.
  • Example: A 200 pixel by 200 pixel true color image (200 x 200 x 3 bytes = 120,000 bytes) can be compressed to smaller file size without changing the image's size or resolution.

File Size Considerations

• For printing: File size is less important, quality is paramount.
• For webpages: File size is critical for fast downloads, quality is also important.

Compression Methods

• Lossless compression: Reduces file size without any loss of data.
  • Good for preserving image integrity.
  • Example: PNG, GIF.
• Lossy compression: Reduces file size by discarding some data.
  • Good for achieving smaller sizes, but sacrifices some quality.
  • Examples: JPEG, JPG.