Images - Png

  • Portable Network Graphic ('ping') - is a raster graphics file format that supports lossless data compression. PNG was created as an improved, non-patented replacement for Graphics Interchange Format (GIF), and is the most widely used lossless image compression format on the
    • 8-bit, 24-bit, 32-bit color
    • alpha channel
  • PNG file size can vary significantly depending on how it is encoded and compressed
    • Color depth
      Color depth can range from 1 to 64 bits per pixel.
    • Ancillary chunks
      PNG supports metadata—this may be useful for editing, but unnecessary for viewing, as on websites.
    • Interlacing
      As each pass of the Adam7 algorithm is separately filtered, this can increase file size.
    • Filter
      As a precompression stage, each line is filtered by a predictive filter, which can change from line to line. As the ultimate DEFLATE step operates on the whole image's filtered data, one cannot optimize this row-by-row; the choice of filter for each row is thus potentially very variable, though heuristics exist
    • Compression
      With additional computation, DEFLATE compressors can produce smaller files.
  • PNG pitfalls
    • Generally larger file size
    • Limited support on older browsers - much older browsers (IE6)