
HTVQEncode |
ptolemy.domains.sdf.lib.vq.HTVQEncode |
This actor encodes a matrix using Hierarchical Table-Lookup Vector
Quantization. The matrix must be of dimensions that are amenable to this
method. (i.e. 2x1, 2x2, 4x2, 4x4, etc.) Instead of performing a
full-search vector quantization during execution, all the optimal encoding
vectors are calculated before hand and stored in a lookup table. (This is
known as Table-lookup Vector Quantization). However, for large vector sizes
the lookup tables are unmanageably large. This actor approximates a
full search VQ by storing the lookup tables hierarchically.
The encoding is broken up into stages, and at each stage a number of 2x1
table lookup VQs are performed. For example,
starting with a 4x2 vector in the first stage, codebook 0 (which operates
on raw pixels) is used 4 times, resulting in a 2x2 vector of codewords.
In the second stage, codebook 1 is used twice, resulting in a 2x1 vector.
Lastly, a single 2x1 VQ using codebook 2 (which operates on codewords
representing 2x2 vectors) returns a single codeword for the 4x2 vector.
<p>
The input is an IntMatrixToken corresponding to the block to be encoded.
The values in this matrix are assumed to be between 0 and 255. The output
is an IntToken with value between 0 and 255. Integers are used here because
of the minimal byte support in Ptolemy or JAVA.
The size of the input matrix should be the same as the parameters blockHeight
and blockWidth.
<p>
The codebook is specified as a binary file that will be read during
initialization. This file actually contains five sets of codebooks and
lookups tables. The first set is for 2x1 blocks, the second is for 2x2
blocks, etc. (Thus the supplied codebook is only sufficient for block sizes
up to 8x4 pixels.) In each set, the codebook precedes the lookup-tables.
The codebook consists of all 256 codevectors, row scanned from top to bottom.
The lookup table consists of 64K entries (one for each pair of codewords from
the previous stage). Each entry in the lookup table is an 8-bit codeword.
<p>
<pre>
Stage 0: 2x1 block size
codebook = 256 blocks x 2 bytes = 512 bytes
lookup tables = 65536 entries x 1 byte = 65536 bytes
Stage 1: 2x2 block size
codebook = 256 blocks x 4 bytes = 1024 bytes
lookup tables = 65536 entries x 1 byte = 65536 bytes
Stage 2: 4x2 block size
codebook = 256 blocks x 8 bytes = 2048 bytes
lookup tables = 65536 entries x 1 byte = 65536 bytes
Stage 3: 4x4 block size
codebook = 256 blocks x 16 bytes = 4096 bytes
lookup tables = 65536 entries x 1 byte = 65536 bytes
Stage 4: 8x4 block size
codebook = 256 blocks x 32 bytes = 8192 bytes
lookup tables = 65536 entries x 1 byte = 65536 bytes
</pre>
<br>
The supplied codebook was trained using images from the
USC image archive and is suitable for most general applications.
<br>
For more information here are some interesting references: <br>
A. Gersho and R. M. Gray, <i>Vector Quantization and Signal Compression</i>.
Kluwer Academic Publishers, Boston, 1992. <br>
P. C. Chang, J. May, R. M. Gray, "Hierarchical Vector Quantizers with
Table Lookup Encoders," <i> International Conference on Acoustics Speech
and Signal Processing</i>, pp. 1452-1455, 1985. <br>
M. Vishwanath and P. Chou, "An Efficient Algorithm for Hierarchical
Compression of Video," <i>International Conference on Image Processing</i>,
vol. 3, pp. 275-279, Nov. 1994. <br>
Author(s): Steve Neuendorffer
Version:$Id: HTVQEncode.doc.html,v 1.1 2006/02/22 18:40:27 mangal Exp $
Pt.Proposed Rating:Yellow (neuendor)
Pt.Accepted Rating:Red (neuendor)
codeBook
A Parameter of type String, giving the location of the codebook data
file relative to the root classpath.
blockCount
The number of blocks to be encoded during each firing.
The default value is one, which will always work, but using a higher
number (such as the number of blocks in a frame) will speed things up.
blockWidth
The width, in pixels, of the block to encode.
blockHeight
The width, in pixels, of the block to encode.
input_tokenConsumptionRate
The input rate.
output_tokenProductionRate
The output rate.