Class HuffmanTablesDirectory

  • public class HuffmanTablesDirectory
    extends Directory
    Directory of tables for the DHT (Define Huffman Table(s)) segment.
    • Constructor Detail

      • HuffmanTablesDirectory

        public HuffmanTablesDirectory()
    • Method Detail

      • getName

        public String getName()
        Description copied from class: Directory
        Provides the name of the directory, for display purposes. E.g. Exif
        Specified by:
        getName in class Directory
        the name of the directory
      • isTypical

        public boolean isTypical()
        Evaluates whether all the tables in this HuffmanTablesDirectory are "typical" Huffman tables.

        "Typical" has a special meaning in this context as the JPEG standard (ISO/IEC 10918 or ITU-T T.81) defines 4 Huffman tables that has been developed from the average statistics of a large set of images with 8-bit precision. Using these instead of calculating the optimal Huffman tables for a given image is faster, and is preferred by many hardware encoders and some hardware decoders.

        Even though the JPEG standard doesn't define these as "standard tables" and requires a decoder to be able to read any valid Huffman tables, some are in reality limited decoding images using these "typical" tables. Standards like DCF (Design rule for Camera File system) and DLNA (Digital Living Network Alliance) actually requires any compliant JPEG to use only the "typical" Huffman tables.

        This is also related to the term "optimized" JPEG. An "optimized" JPEG is a JPEG that doesn't use the "typical" Huffman tables.

        Whether or not all the tables in this HuffmanTablesDirectory are the predefined "typical" Huffman tables.
      • isOptimized

        public boolean isOptimized()
        The opposite of isTypical().
        Whether or not the tables in this HuffmanTablesDirectory are "optimized" - which means that at least one of them aren't one of the "typical" Huffman tables.