Scalar Quantizer (Obsolete)

Convert input signal into set of quantized output values or index values, or convert set of index values into quantized output signal

Library

dspobslib

• 

Description

Note

The Scalar Quantizer block is still supported but is likely to be obsoleted in a future release. We strongly recommend replacing this block with the Scalar Quantizer Encoder block or the Scalar Quantizer Decoder block.

The Scalar Quantizer block has three modes of operation. In Encoder mode, the block maps each input value to a quantization region by comparing the input value to the quantizer boundary points defined in the Boundary points parameter. The block outputs the index of the associated region. In Decoder mode, the block transforms the input index values into quantized output values, defined in the Codebook parameter. In the Encoder and Decoder mode, the block performs both the encoding and decoding operations. The block outputs the index values and the quantized output values.

You can select how you want to enter the Boundary points and/or Codebook values using the Source of quantizer parameters. When you select Specify via dialog, type the parameters into the block parameters dialog box. Select Input ports, and port B and/or C appears on the block. In Encoder and Encoder and decoder mode, the input to port B is used as the Boundary points. In Decoder and Encoder and decoder mode, the input to port C is used as the Codebook.

In Encoder and Encoder and decoder mode, the Boundary points are the values used to break up the input signal into regions. Each region is specified by an index number. When your first boundary point is -inf and your last boundary point is inf, your quantizer is unbounded. When your first and last boundary point is finite, your quantizer is bounded. When only your first or last boundary point is -inf or inf, your quantizer is semi-bounded.

For instance, when your input signal ranges from 0 to 11, you can create a bounded quantizer using the following boundary points:

[0 0.5 3.7 5.8 6.0 11] 

The boundary points can have equal or varied spacing. Any input values between 0 and 0.5 would correspond to index 0. Input values between 0.5 and 3.7 would correspond to index 1, and so on.

Suppose you wanted to create an unbounded quantizer with the following boundary points:

[-inf 0 2 5.5 7.1 10 inf] 

When your input signal has values less than 0, these values would be assigned to index 0. When your input signal has values greater than 10, these values would be assigned to index 6.

When an input value is the same as a boundary point, the Tie-breaking rule parameter defines the index to which the value is assigned. When you want the input value to be assigned to the lower index value, select Choose the lower index. To assign the input value with the higher index, select Choose the higher index.

In Decoder and Encoder and decoder mode, the Codebook is a vector of quantized output values that correspond to each index value.

In Encoder and Encoder and decoder mode, the Searching method determines how the appropriate quantizer index is found. Select Linear and the Scalar Quantizer block compares the input value to the first region defined by the first two boundary points. When the input value does not fall within this region, the block then compares the input value to the next region. This process continues until the input value is determined to be within a region and is associated with the appropriate index value. The computational cost of this process is of the order P, where P is the number of boundary points.

Select Binary for the Searching method and the block compares the input value to the middle value of the boundary points vector. When the input value is larger than this boundary point, the block discards the boundary points that are lower than this middle value. The block then compares the input value to the middle boundary point of the new range, defined by the remaining boundary points. This process continues until the input value is associated with the appropriate index value. The computational cost of this process is of the order log₂P, where P is the number of boundary points. In most cases, the Binary option is faster than the Linear option.

In Decoder mode, the input to this block is a vector of index values, where 0 ≤ index <N and N is the length of the codebook vector. Use the Action for out of range input parameter to determine what happens when an input index value is out of this range. When you want any index values less than 0 to be set to 0 and any index values greater than or equal to N to be set to N -1, select Clip. When you want to be warned when any index values less than 0 are set to 0 and any index values greater than or equal to N are set to N -1, select Clip and warn. When you want the simulation to stop and display an error when the index values are out of range, select Error.

In Encoder and decoder mode, you can select the Output the quantization error check box. The quantization error is the difference between the input value and the quantized output value. Select this check box to output the quantization error for each input value from the Err port on this block.

Data Type Support

In Encoder mode, the input data values and the boundary points can be the input to the block at ports U and B. Similarly, in Encoder and decoder mode, the codebook values can also be the input to the block at port C. The data type of the input data values, boundary points, and codebook values can be double, single, uint8, uint16, uint32, int8, int16, or int32. In Decoder mode, the input to the block can be the index values and the codebook values. The data type of the index input to the block at port Idx can be uint8, uint16, uint32, int8, int16, or int32. The data type of the codebook values can be double, single, uint8, uint16, uint32, int8, int16, or int32.

In Encoder mode, the output of the block is the index values. In Encoder and decoder mode, the output can also include the quantized output values and the quantization error. In Encoder and Encoder and decoder mode, use the Output index data type parameter to specify the data type of the index output from the block at port Idx. The data type of the index output can be uint8, uint16, uint32, int8, int16, or int32. The data type of the quantized output and the quantization error can be double, single, uint8, uint16, uint32, int8, int16, or int32. In Decoder mode, the output of the block is the quantized output values. Use the Output data type parameter to specify the data type of the quantized output values. The data type can be double, single, uint8, uint16, uint32, int8, int16, int32.

Note

The input data, codebook values, boundary points, quantization error, and the quantized output values must have the same data type whenever they are present in any of the quantizer modes.

Parameters

Quantizer mode

Specify Encoder, Decoder, or Encoder and decoder as a mode of operation.

Source of quantizer parameters

Choose Specify via dialog to type the parameters into the block parameters dialog box. Select Input ports to specify the parameters using the block's input ports. In Encoder and Encoder and decoder mode, input the Boundary points using port B. In Decoder and Encoder and decoder mode, input the Codebook values using port C.

Boundary points

Enter a vector of values that represent the boundary points of the quantizer regions. Tunable (Simulink).

Codebook

Enter a vector of quantized output values that correspond to each index value. Tunable (Simulink).

Searching method

Select Linear and the block finds the region in which the input value is located using a linear search. Select Binary and the block finds the region in which the input value is located using a binary search.

Tie-breaking rule

Set this parameter to determine the behavior of the block when the input value is the same as the boundary point. When you select Choose the lower index, the input value is assigned to lower index value. When you select Choose the higher index, the value is assigned to the higher index.

Action for out of range input

Choose the block's behavior when an input index value is out of range, where 0 ≤ index <N and N is the length of the codebook vector. Select Clip, when you want any index values less than 0 to be set to 0 and any index values greater than or equal to N to be set to N -1. Select Clip and warn, when you want to be warned when any index values less than 0 are set to 0 and any index values greater than or equal to N are set to N -1. Select Error, when you want the simulation to stop and display an error when the index values are out of range.

Output the quantization error

In Encoder and decoder mode, select this check box to output the quantization error from the Err port on this block.

Output index data type

In Encoder and Encoder and decoder mode, specify the data type of the index output from the block at port Idx. The data type can be uint8, uint16, uint32, int8, int16, or int32. This parameter becomes visible when you select the Show additional parameters check box.

Output data type

In Decoder mode, specify the data type of the quantized output. The data type can be uint8, uint16, uint32, int8, int16, int32, single, or double. This parameter becomes visible when you select Specify via dialog for the Source of quantizer parameters and you select the Show additional parameters check box.

References

Gersho, A. and R. Gray. Vector Quantization and Signal Compression. Boston: Kluwer Academic Publishers, 1992.

Supported Data Types

• Double-precision floating point

• Single-precision floating point

• Fixed point

• 8-, 16-, and 32-bit signed integers

• 8-, 16-, and 32-bit unsigned integers

For more information on what data types are supported for each quantizer mode, see Data Type Support.