Tuesday, February 19, 2013

Data Compression

Data compression is a method of reducing the file size for conserving drive space or easier transfer. Data compression comes in three forms:

  • Archival
    • A lossless method of packing a file into a smaller space.
    • The file will need to be unpacked before using.
    • Also useful for collecting multiple files into one package for transfer.
    • Examples include zip, rar, tar, gz.
  • Lossless
    • A method of reducing the size of a file by removing statistical redundancies.
    • When the file is decompressed, the result should be identical to the original.
    • The file is decompressed by the decoder in real-time for consumption.
    • Examples include flac, alac.
  • Lossy
    • A method of reducing the size of a file by removing irrelevant information.
      • The information is gone forever.
    • Irrelevancy of information is determined by the codec used.
      • The codec determines irrelevant information based on psychovisual or psychoacoustic models.
    • Benefits include reduced disk space and bandwidth use.
    • Examples include jpeg, mp3.

Sunday, February 17, 2013

Compression Artifacts

Compression reduces the data needed to represent the image, audio, or video. During lossy compression, artifacts (errors) are created as a side effect. These artifacts may or may not have an impact on the quality of the resultant file. Whether or not this occurs is based on the complexity of the algorithm used during compression.

Processing power and compression algorithms are interrelated. A more powerful processor can execute a more complex algorithm more efficiently (i.e.: in less time). A newer, more complex compression algorithm can be introduced because newer, more powerful processors can handle it.

Thursday, February 14, 2013

Free Images Online

Color Spaces

  • RGB is used for illuminating color
    • Red, Green, and Blue light are added together
  • YUV is used for transmitting color
    • YCbCr is the digital version
    • Y is the luminance
    • U is the blue-difference
    • V is the red-difference
  • CMYK is used for printing color
  • HSV is used in digital image editing
    • Hue, Saturation, Value

Color Spaces on Wikipedia.