SYNOPSISpvrg-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]
[[-ci ComponentIndex2] [-fw FrameWidth2] [-fh FrameHeight2]
[-hf HorizontalFrequency2] [-vf VerticalFrequency2]
DESCRIPTIONpvrg-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.
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.
- specifies the height of the tallest component. This corresponds to the height of the ``original image''.
- specifies that a JFIF header is placed on the encoded stream. This is unnecessary for decoding.
- 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.
- enables the double-precision floating point Reference DCT. (Default is Chen DCT.)
- enables the Lee DCT. (Default is Chen DCT.)
- enables decoding. See below.
- 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.
- 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.
- signals that the command interpreter will read from the standard input.
- 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.
- for decoding only, signals that no resynchronization is enabled, thus ignore any markers found in the data stream.
- 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.
- 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.
is the place to load(decoder)/store(encoder)
the coded image--if unspecified it defaults to
For every component in the image we have:
- 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.
- 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).
- 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.
- specifies the block sampling frequency of the component in the horizontal direction for every MDU transmitted.
- 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.
- represents the directory path location of the nth component file.
EXAMPLESIn 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
The images can also be converted to ppm and back through
Those utility programs available by anonymous ftp from
There are many more options within an internal command interpreter. Please see the accompanying documentation in doc.ps for more details.
BUGSSomewhat 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.