Video and Image Processing Blockset™

2-D Histogram (Obsolete) - Generate histogram of each input matrix

Library

Statistics

Description

Note   The 2-D Histogram block is obsolete. It may be removed in a future version of the Video and Image Processing Blockset™. Use the replacement block Histogram.

The 2-D Histogram block computes the frequency distribution of the elements in each input matrix or in a sequence of inputs over a period of time. Use the Running histogram check box to select between the block's basic and running operation.

The output of the 2-D Histogram block is different than the output of the imhist function in the Image Processing Toolbox™. For intensity images, the imhist function defines the pth bin boundaries as

where A is maximum value of the data type, N is the number of bins in the histogram, and p starts from 1. The 2-D Histogram block defines bin boundaries as

where A corresponds to the Maximum value of input parameter and the Minimum value of input parameter is assumed to be 0.

Length-M 1-D vector inputs are treated as M-by-1 column vectors.

The block sorts the elements of each input matrix into the number of discrete bins, n, specified by the Number of bins parameter. Complex inputs are sorted by their magnitude squared values.

The histogram value for a given bin represents the frequency of occurrence of the input values bracketed by that bin. You specify the upper boundary of the highest-valued bin in the Maximum value of input parameter, B_M, and the lower boundary of the lowest-valued bin in the Minimum value of input parameter, B_m. The bins have equal width of

where n is the number of bins. The centers are located at

Input values that fall on the border between two bins are sorted into the lower-valued bin; that is, each bin includes its upper boundary. For example, a bin of width 4 centered on the value 5 contains the input value 7, but not the input value 3. Input values greater than the Maximum value of input parameter or less than Minimum value of input parameter are sorted into the highest-valued or lowest-valued bin, respectively. The values you enter for the Maximum value of input and Minimum value of input parameters must be real-valued scalar values.

Basic Operation

If you clear the Running histogram check box, the block computes the frequency distribution of each M-by-N input matrix and outputs a sample-based 1-by-N vector.

For example, if your input is and you set the block parameters as follows:

• Minimum value of input = 0

• Maximum value of input = 4

• Number of bins = 4

The block outputs [3 3 3 0].

If you select the Normalized check box, the block scales each element of the output so that sum(v) is 1, where v is the output vector.

Running Operation

If you select the Running histogram check box, the block computes the frequency distributions in a series of M-by-N inputs.

For example, if your first input is , your second and current input is , and you set the block parameters as follows:

• Minimum value of input = 0

• Maximum value of input = 4

• Number of bins = 4

The block outputs [3 6 6 3]. For the next input, the block computes the frequency distribution for the first three inputs, and so on.

Resetting the Running Histogram

The block resets the running histogram whenever a reset event is detected at the optional Rst port. The reset signal and the input data signal must be the same rate.

To enable the Rst port, select the Reset port parameter. You specify the reset event in the Trigger type parameter, and can be one of the following:

• Rising edge — Triggers a reset operation when the Rst input does one of the following:

  • Rises from a negative value to a positive value or 0

  • Rises from 0 to a positive value, where the rise is not a continuation of a rise from a negative value to 0 (see the following figure)

• Falling edge — Triggers a reset operation when the Rst input does one of the following:

  • Falls from a positive value to a negative value or 0

  • Falls from zero to a negative value, where the fall is not a continuation of a fall from a positive value to 0 (see the following figure)

    

• Either edge -- Triggers a reset operation when the Rst input is a Rising edge or Falling edge (as described previously)

• Non-zero sample -- Triggers a reset operation at each sample time that the Rst input is not 0

Note   When running simulations in the Simulink® MultiTasking mode, sample-based reset signals have a one-sample latency, and frame-based reset signals have one frame of latency. Thus, there is a one-sample or one-frame delay between the time the block detects a reset event, and when it applies the reset. For more information on latency and the Simulink tasking modes, see Configuration Parameters Dialog Box in the Simulink documentation.

Dialog Box

The Main pane of the 2-D Histogram dialog box:

Minimum value of input

Enter a real-valued scalar value for the lower boundary, , of the lowest-valued bin. Tunable.

Maximum value of input

Enter a real-valued scalar value for the upper boundary, , of the highest-valued bin. Tunable.

Number of bins

Enter the number of bins, n, in the histogram.

Normalized

If you select this check box, the block normalizes the output vector (1-norm). Tunable.

Use of this parameter is not supported for fixed-point signals.

Running histogram

Select this check box to enable the block's running histogram operation.

Reset port

Enables the Rst input port when selected. The reset signal and the input data signal must be the same rate. This parameter is visible if you select the Running histogram check box.

Trigger type

The type of event that resets the running histogram. For more information, see Resetting the Running Histogram. This parameter is enabled only when you set the Reset port parameter.

The Fixed-point pane of the 2-D Histogram dialog box:

Note   The fixed-point parameters are only used for fixed-point complex inputs, which are sorted by squared magnitude.

Rounding mode

Select the rounding mode for fixed-point operations.

Overflow mode

Select the overflow mode for fixed-point operations.

Product output

Use this parameter to specify how to designate the product output word and fraction lengths:

• When you select Same as input, these characteristics match those of the input to the block.

• When you select Binary point scaling, you can enter the word length and the fraction length of the product output, in bits.

• When you select Slope and bias scaling, you can enter the word length, in bits, and the slope of the product output. This block requires power-of-two slope and a bias of 0.

Accumulator

Use this parameter to specify the accumulator word and fraction lengths resulting from a complex-complex multiplication in the block:

• When you select Same as product output, these characteristics match those of the product output.

• When you select Same as input, these characteristics match those of the input to the block.

• When you select Binary point scaling, you can enter the word length and the fraction length of the accumulator, in bits.

• When you select Slope and bias scaling, you can enter the word length, in bits, and the slope of the accumulator. This block requires power-of-two slope and a bias of 0.

Lock scaling against changes by the autoscaling tool

Select this parameter to prevent any fixed-point scaling you specify in this block mask from being overridden by the autoscaling tool in the Fixed-Point Tool. For more information, see fxptdlg, a reference page on the Fixed-Point Tool in the Simulink documentation.

See Also

2-D FIR Filter

2-D IDCT