IDCT
Inverse discrete cosine transform (IDCT) of input
Libraries:
DSP System Toolbox /
Transforms
Description
The IDCT block computes the inverse discrete cosine transform (IDCT) of the input signal u. When the input is an M-by-N matrix, the block computes the IDCT of each channel in the matrix.
Here is the equivalent MATLAB® code.
y = idct(u)
Ports
Input
Input 1 — Input signal
vector | matrix | N-D array
Specify the input signal as a vector, matrix, or an N-D array.
For all N-D input arrays, the block computes the IDCT across the first dimension. The size of the first dimension (frame size) must be a power of two. To work with other frame sizes, use the Pad block to pad or truncate the frame size to a power-of-two length.
When the input is an M-by-N matrix, the block treats each input column as an independent channel containing M consecutive samples.
Data Types: single
| double
| int8
| int16
| int32
| uint8
| uint16
| uint32
| fixed point
| bus
Complex Number Support: Yes
Output
Output 1 — IDCT output
vector | matrix | N-D array
The block outputs the IDCT of the input signal as a vector, matrix, or an N-D array.
When the block outputs an M-by-N matrix, the lth column contains the length-M IDCT of the corresponding input column.
where
When the input is fixed-point (signed and unsigned), the output is signed fixed-point.
Data Types: single
| double
| int8
| int16
| int32
| fixed point
| bus
Complex Number Support: Yes
Parameters
Main Tab
Sine and cosine computation — Sine and cosine computation
Table lookup
(default) | Trigonometric fcn
Set the block to compute sines and cosines by either looking up sine and cosine values
in a speed-optimized table (Table lookup
), or
by making sine and cosine function calls (Trigonometric
fcn
).
To compute sines and cosines, set the parameter to one of these values:
Table lookup
–– The block computes and stores the trigonometric values before the simulation starts, and retrieves them during the simulation. When you generate code from the block, the processor running the generated code stores the trigonometric values computed by the block in a speed-optimized table, and retrieves the values during code execution.The block runs much more quickly, but requires extra memory for storing the precomputed trigonometric values.
Trigonometric fcn
–– The block computes sine and cosine values during the simulation. When you generate code from the block, the processor running the generated code computes the sine and cosine values while the code runs.The block runs more slowly, but does not need extra data memory. For code generation, the block requires a support library to emulate the trigonometric functions, increasing the size of the generated code.
Data Types Tab
Rounding mode — Rounding mode
Floor
(default) | Ceiling
| Convergent
| Nearest
| Round
| Simplest
| Zero
Select the rounding
mode for fixed-point operations. The sine table values do not
obey this parameter; they always round to
Nearest
.
Saturate on integer overflow — Saturate on integer overflow
off
(default) | on
When you select this parameter, the block saturates the result of its
fixed-point operation. When you clear this parameter, the block wraps
the result of its fixed-point operation. For details on
saturate
and wrap
, see overflow
mode for fixed-point operations.
Note
The Rounding mode and Saturate on integer overflow parameters have no effect on numeric results when these conditions are met:
Product output data type is
Inherit: Inherit via internal rule
.Accumulator data type is
Inherit: Inherit via internal rule
.
With these data type settings, the block operates in full-precision mode.
Sine table — Sine table
Inherit: Same word length as
input
(default) | fixdt(1,16)
Choose how you specify the word length of the values of the sine table. The fraction length of the sine table values always equals the word length minus one. You can set this parameter to:
A rule that inherits a data type, for example,
Inherit: Same word length as input
An expression that evaluates to a valid data type, for example,
fixdt(1,16)
The sine table values do not obey the Rounding mode and
Saturate on integer overflow parameters. The
block always saturates and rounds off the sine table values to
Nearest
.
Product output — Product output
Inherit: Inherit via internal
rule
(default) | Inherit: Same as input
| fixdt(1,16,0)
Specify the product output data type. See Fixed-Point Data Types and Multiplication Data Types for illustrations depicting the use of the product output data type in this block. You can set this parameter to:
A rule that inherits a data type, for example,
Inherit: Inherit via internal rule
. For more information on this rule, see Inherit via Internal Rule.An expression that evaluates to a valid data type, for example,
fixdt(1,16,0)
Click the Show data type assistant button to display the Data Type Assistant, which helps you set the Product output parameter.
See Specify Data Types Using Data Type Assistant (Simulink) for more information.
Accumulator — Accumulator
Inherit: Inherit via internal
rule
(default) | Inherit: Same as input
| Inherit: Same as product output
| fixdt(1,16,0)
Specify the accumulator data type. See Fixed-Point Data Types for illustrations depicting the use of the accumulator data type in this block. You can set this parameter to:
A rule that inherits a data type, for example,
Inherit: Inherit via internal rule
. For more information on this rule, see Inherit via Internal Rule.An expression that evaluates to a valid data type, for example,
fixdt(1,16,0)
Click the Show data type assistant button to display the Data Type Assistant, which helps you set the Accumulator parameter.
See Specify Data Types Using Data Type Assistant (Simulink) for more information.
Output — Output data type
Inherit: Inherit via internal
rule
(default) | Inherit: Same as input
| fixdt(1,16,0)
Specify the output data type. See Fixed-Point Data Types for illustrations depicting the use of the output data type in this block. You can set this parameter to:
A rule that inherits a data type, for example,
Inherit: Inherit via internal rule
.When you select
Inherit: Inherit via internal rule
, the block calculates the output word length and fraction length automatically. The internal rule first calculates an ideal output word length and fraction length using the following equations:Using these ideal results, the internal rule then selects word lengths and fraction lengths that are appropriate for your hardware. For more information, see Inherit via Internal Rule.
An expression that evaluates to a valid data type, for example,
fixdt(1,16,0)
Click the Show data type assistant button to display the Data Type Assistant, which helps you set the Output parameter.
See Control Data Types of Signals (Simulink) for more information.
Output Minimum — Output minimum
[]
(default) | scalar
Specify the minimum value that the block should output. The default
value is []
(unspecified). Simulink® software uses this value to perform:
Simulation range checking (see Specify Signal Ranges (Simulink))
Automatic scaling of fixed-point data types
Output Maximum — Output Maximum
[]
(default) | scalar
Specify the maximum value that the block should output. The default
value is []
(unspecified). Simulink software uses this value to perform:
Simulation range checking (see Specify Signal Ranges (Simulink))
Automatic scaling of fixed-point data types
Lock data type settings against changes by the fixed-point tools — Prevent fixed-point tools from overriding data types
off
(default) | on
Select this parameter to prevent the fixed-point tools from overriding the data types you specify in the block dialog box.
Block Characteristics
Data Types |
|
Direct Feedthrough |
|
Multidimensional Signals |
|
Variable-Size Signals |
|
Zero-Crossing Detection |
|
More About
Fixed-Point Data Types
The following diagrams show the data types used within the IDCT block for fixed-point signals. You can set the sine table, accumulator, product output, and output data types displayed in the diagrams in the block parameters dialog box of the IDCT block.
Inputs to the IDCT block are first cast to the output data type and stored in the output buffer. Each butterfly stage processes signals in the accumulator data type, with the final output of the butterfly being cast back into the output data type.
The output of the multiplier is in the product output data type when at least one of the inputs to the multiplier is real. When both of the inputs to the multiplier are complex, the result of the multiplication is in the accumulator data type. For details on the complex multiplication performed, see Multiplication Data Types.
Note
When the block input is fixed point, all internal data types are signed fixed point.
Extended Capabilities
C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.
Generated code relies on the memcpy
or
memset
function (string.h
) under certain
conditions.
To comply with the embedded systems coding standards, generated code is non-recursive.
Fixed-Point Conversion
Design and simulate fixed-point systems using Fixed-Point Designer™.
Version History
Introduced before R2006a
MATLAB コマンド
次の MATLAB コマンドに対応するリンクがクリックされました。
コマンドを MATLAB コマンド ウィンドウに入力して実行してください。Web ブラウザーは MATLAB コマンドをサポートしていません。
Select a Web Site
Choose a web site to get translated content where available and see local events and offers. Based on your location, we recommend that you select: .
You can also select a web site from the following list:
How to Get Best Site Performance
Select the China site (in Chinese or English) for best site performance. Other MathWorks country sites are not optimized for visits from your location.
Americas
- América Latina (Español)
- Canada (English)
- United States (English)
Europe
- Belgium (English)
- Denmark (English)
- Deutschland (Deutsch)
- España (Español)
- Finland (English)
- France (Français)
- Ireland (English)
- Italia (Italiano)
- Luxembourg (English)
- Netherlands (English)
- Norway (English)
- Österreich (Deutsch)
- Portugal (English)
- Sweden (English)
- Switzerland
- United Kingdom (English)