Main

-Developer functions detailed descriptions

-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

-

-packJPG contains functionality especially designed for developers. This

-document details how to use the developer functions.

-

-

-Developer switches

-~~~~~~~~~~~~~~~~~~

-

- -dev needed to enable any of the switches bewlow

-

- -test test algorithms, alert if error

- -split split jpeg (to header & image data)

- -coll? write coefficients (0=std,1=dhf,2=squ,3=unc)

- -fcol? write filtered coefficients (see above)

- -zdst write zero distribution lists to files

- -info write debug info to .nfo file

- -dist write distribution data to file

- -pgm convert and write to pgm files

-

- -s? set global number of segments (1<=s<=49)

- -t? set global noise threshold (0<=t<=10)

- -s?,? set number of segments for component

- -t?,? set noise threshold for component

-

-

-Developer switches usage

-~~~~~~~~~~~~~~~~~~~~~~~~

-

-The developer switch "-ver" is needed the enable any developer function.

-Other developer functions won't work without it.

-

-"-test" is a special case of the "-ver" option. Files are also verified,

-but if any error happens, all the output will be kept for the developer

-to have a look at it.

-

-"-split" splits a JPEG file to huffman coded image data and header data.

-This mode is useful if a closer look at the header of a given file is

-needed.

-

-"-coll?" and "-fcol?" write decompressed DCT coefficients to separate

-files (one for each color component). DCT coefficients are stored in two

-byte signed short integers. In the "-fcol?" option, DC coefficents are

-replaced by the corresponding DC prediction errors, while using the

-"-coll?" option will dump DC coeffcients without any prediction applied.

-The "?" has to be replaced by a number 0, 1, 2 or 3, which will

-determine the order the coefficients will be stored inside the files.

-Have a look at the included sample images or the source code to get an

-idea on which each number stands for.

-

-"-zdst" writes zero distribution lists to files (one for each color

-component). For each 8x8 image data block in a given color component, a

-zero distribution list contains the number of coefficients unequal zero.

-These numbers are stored as unsigned one byte chars. In packJPG, zero

-distribution lists are used as a replacement for JPEGs EOB symbol and

-for segmentation of data.

-

-"-info" dumps a ".nfo" text file with data about the JPEG file.

-Structure of header, type of coding and quantization tables for each

-component are included in this file.

-

-"-dump" dumps distribution for a given file to ".dist" files (again, one

-file per color component). For each band seperately this files contain

-the number of coefficients = 0; 1; 2; 3; 4; .... (absolute values). Have

-a look at the source code to get an idea about the structure of these

-files.

-

-"-pgm" mainly serves as a test function for the integrated DCT routines.

-Each color component is transformed back to it's image representation

-using the IDCT and dumped seperately as a ".PGM" (Portable GrayMap)

-file.

-

-"-t?" and "-s?" control specific compression settings. By manipulating

-these parameters, you might achieve higher compression. By default,

-these values are set automatically. The default for segmentation ("-s?")

-is 10. The default for the noise threshold ("-t?") is dependant on the

-size of the input file. Higher sizes mean higher t - theres more data

-for the statistical model to learn in bigger files, so less has to be

-considered noise.

-

-

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-packJPG by Matthias Stirner, 11/2011