Vector.IDCT Method

Overload List

#	Signature	Description
1	function IDCT: TVec;	Calculate the inverse DCT in-pllace.
2	function IDCT(const Vec: TVec): TVec;	The inverse discrete cosine transform (DCT).
3	function IDCT(const Vec: TMtxVec; VecIndex: Integer; Index: Integer; Len: Integer): TMtxVec;	The inverse discrete cosine transform (DCT).

Overload 1: function IDCT: TVec;

Calculate the inverse DCT in-pllace.

Result: stored in self (calling object), returns self for chaining

Remarks:

The length of the calling vector is adjusted automatically.

Overload 2: function IDCT(const Vec: TVec): TVec;

The inverse discrete cosine transform (DCT).

#	Name	Type	Description
1	Vec	TVec

Result: stored in self (calling object), returns self for chaining

Remarks:

Calculates the inverse discrete cosine transform (DCT) of a Vec and writes the results in the calling vector. If Vec Vector.Length is a power of 2, the function uses an efficient algorithm that is significantly faster than the direct computation of DCT. For other values of Vec length, this function uses the direct formulas given below; however, the symmetry of cosine function is taken into account, which allows to perform about half of the multiplication operations in the formulas. In the following definition of inverse DCT, N=Vec.Length and V is the calling vector:

\begin{aligned} C(k) &= \begin{cases} \sqrt{\frac{1}{N}} & k=0 \\ \sqrt{\frac{2}{N}} & k > 0 \end{cases} \\ \text{V}[k] &= C(k)\cdot \text{Vec}[k]\sum _{n=0} ^{N-1} \cos \left( \frac{(2n+1)k\pi}{2N}\right) \end{aligned}

Examples

var a,b: Vector;
begin
    a.SetIt(False,[1,-2,3,4]);
    b.IDCT(a);
end;

See Also: Vector.DCT

Overload 3: function IDCT(const Vec: TMtxVec; VecIndex: Integer; Index: Integer; Len: Integer): TMtxVec;

The inverse discrete cosine transform (DCT).

#	Name	Type	Description
1	Vec	TMtxVec
2	VecIndex	Integer
3	Index	Integer	start index
4	Len	Integer	element count

Result: stored in self (calling object), returns self for chaining

Remarks:

Calculate the inverse discrete cosine transform (DCT) from Vec elements [VecIndex]..[VecIndex+Len-1] and store the results in the calling object elements [Index]..[Index+Len-1]. The Len parameter must be the power of two. Size and Vector.Complex properties of the calling vector must be set explicitly. An exception is raised if Vector.ConditionCheck is True and array borders are overrun.