Provided by: pvrg-jpeg_1.2.1+dfsg1-4_amd64 
NAME
pvrg-jpeg - JPEG compression and decompression
SYNOPSIS
pvrg-jpeg -iw ImageWidth -ih ImageHeight [-JFIF] [-q(l) Q-Factor]
[-a] [-b] [-d] [-k predictortype] [-n] [-O] [-y] [-z] [-g]
[-p PrecisionValue] [-t pointtransform]
[-r ResyncInterval] [-s StreamName] [-o OutBaseName]
[[-ci ComponentIndex1] [-fw FrameWidth1] [-fh FrameHeight1]
[-hf HorizontalFrequency1] [-vf VerticalFrequency1]
ComponentFile1]
[[-ci ComponentIndex2] [-fw FrameWidth2] [-fh FrameHeight2]
[-hf HorizontalFrequency2] [-vf VerticalFrequency2]
ComponentFile2]
....
DESCRIPTION
pvrg-jpeg is a still-image compression/decompression program that performs JPEG encoding and decoding of
multiple raster-scanned files.
These ``raster-scanned files'' are basically PGM (portable graymap) files without the PGM header. A
typical JPEG image is made of three of these files representing the Y, Cr, and Cb color channels. Usually
the Y (lumience) channel is full size, while the two chroma channels are half width and half height. But
no particular channel really needs to be full size, so pvrg-jpeg will need to know the dimensions of the
original image when creating jpegs.
OPTIONS
ImageWidth
specifies the width of the original image. This should correspond to the width of the widest
component and, thus, the width of the ``original image''. All components have widths roughly
corresponding to an integer decimation ratio from this specification.
ImageHeight
specifies the height of the tallest component. This corresponds to the height of the ``original
image''.
-JFIF specifies that a JFIF header is placed on the encoded stream. This is unnecessary for decoding.
Q-Factor
option specifies a multiplicative factor for the quantization: each quantization coefficient of
the default matrix is scaled by (Q-Factor/50). A Q-Factor of 0 is the same thing as a Q-Factor of
50 because it disables this function. -q specifies an 8 bit quantization matrix; -ql specifies a
16 bit quantization matrix, useful for 12 bit data.
-a enables the double-precision floating point Reference DCT. (Default is Chen DCT.)
-b enables the Lee DCT. (Default is Chen DCT.)
-d enables decoding. See below.
-g This option will put PGM headers on output files when decoding.
-k predictortype
The lossless predictor type, specified as an integer between 1-7. If specified, then lossless
mode is used.
-n This option specifies that the files should not be transmitted in interleaved format.
-o OutBaseName
This will use specified string as a base name for output files when decoding.
-O signals that the command interpreter will read from the standard input.
-p Specifies the precision. Normally should be between 2-16 for lossless; 8 or 12 for DCT. If it is
specified as a number greater than 8 then the input is considered to be unsigned shorts (16 bits,
msb first). Not aggressively checked.
-s JPEGStreamName
When encoding, this will be used as the output file. When decoding, this will be used as the input
file.
-t pointtransform
Specifies the shifting (right) upon loading input and shifting (left) upon writing input.
Generally used by the lossless mode only. Can be used by the DCT mode to add or subtract bits.
-y for decoding only, signals that no resynchronization is enabled, thus ignore any markers found in
the data stream.
-z enables use of default Huffman tables. This converts the coding from a two-pass system using the
first pass to generate custom tables to a one-pass system using internal default tables. With this
option, the compression speed is nearly doubled, but because the internal tables are not custom to
the image, the compressed file size increases slightly.
ResyncInterval
specifies a resync (restart) interval for the input file--if set to 0 (default), resynchronization
is disabled; otherwise it signifies the number of MDU between a resync marker.
StreamName
is the place to load(decoder)/store(encoder) the coded image--if unspecified it defaults to
ComponentFile1.jpg.
For every component in the image we have:
ComponentIndex
describes the component index where the file data should be associated with. The possible values
are between 0 and 255. As a rule Y is in 1; U is in 2; V is in 3. The file specfications, if
left undisturbed, will result in component location of 1 for the first component file, 2 for the
second component file, and so on. If -ci is specified for the previous component file, then the
next component index defaults to the previous component index plus 1.
FrameWidth
describes the actual width of the component. This should be determinable by the size of the
original image (ImageHeight and ImageWidth) and the frequency sampling of that component. This
program assumes that the sampling component will be round up to the nearest integer and other
programs may not necessarily follow that convention, we allow precise specification of the
FrameWidth. The program will notify the user if the framewidth and frameheight specifications do
not correspond to a logical MDU pattern and thus will refuse to take the input (in fact, sometimes
rounding down will not result in a logical MDU pattern).
FrameHeight
describes the actual height of the component. Multiplied together with FrameWidth, this should
equal the file size of the component. See the above discussion on the actual specification.
Hor-Frequency
specifies the block sampling frequency of the component in the horizontal direction for every MDU
transmitted.
Ver-Frequency
specifies the block sampling frequency of the component in the vertical direction. When multiplied
together with the Horizontal frequency, it corresponds to the number of blocks of that component
in the MDU.
ComponentFilen
represents the directory path location of the nth component file.
EXAMPLES
In order to encode a set of raster-scanned files: 128x128 in image.Y; 64x128 in image.U; and 64x128 in
image.V into the file image.jpg, the command is
pvrg-jpeg -iw 128 -ih 128 -hf 2 image.Y image.U image.V -s image.jpg
In order to decode a compressed file in image.jpg, type
pvrg-jpeg -d -s image.jpg
The three output files will be in image.jpg.1 image.jpg.2 image.jpg.3. The images can be displayed by
the cv program. The images can also be converted to ppm and back through the programs cyuv2ppm and
ppm2cyuv Those utility programs available by anonymous ftp from
havefun.stanford.edu:pub/cv/CVv1.2.1.tar.Z.
There are many more options within an internal command interpreter. Please see the accompanying
documentation in doc.ps for more details.
BUGS
Somewhat slower than many commercial implementations, some bugs are probably lurking around. Lossless
coding and decoding are especially slow. This program can produce jpeg files that other programs cannot
understand.
AUTHOR
Andy Hung