AlphaComp

Combines two images using alpha (opacity) values of both images.

Syntax

IppStatus ippiAlphaComp_<mod>(const Ipp<datatype>* pSrc1, int src1Step, const Ipp<datatype>* pSrc2, int src2Step, Ipp<datatype>* pDst, int dstStep, IppiSize roiSize, IppiAlphaType alphaType);

Supported values for mod:

8u_AC1R	8s_AC1R	16u_AC1R	16s_AC1R	32u_AC1R	32s_AC1R	32f_AC1R
8s_AC1R	16u_AC1R	16s_AC1R	8u_AC4R	32u_AC4R	32s_AC4R	32f_AC4R

IppStatus ippiAlphaComp_<mod>(const Ipp<datatype>* constpSrc1[4], int src1Step, const Ipp<datatype>* const pSrc2[4], int src2Step, Ipp<datatype>* const pDst[4], int dstStep, IppiSize roiSize, IppiAlphaType alphaType);

Supported values for mod:

8u_AP4R

16u_AP4R

Parameters

pSrc1, pSrc2	Pointers to the source image ROI for pixel-order data. An array of pointers to ROI in the separate source color planes in case of planar data.
src1Step, src2Step	Distances in bytes between starts of consecutive lines in the source images.
pDst	Pointer to the destination image ROI for pixel-order data. An array of pointers to ROI in the separate destination color planes in case of planar data.
dstStep	Distance in bytes between starts of consecutive lines in the destination image.
roiSize	Size of the source and destination ROI in pixels.
alphaType	The composition type to perform. See Table “Possible Values of the Parameter alphaType” for the type value and description.

Description

The function ippiAlphaComp is declared in the ippi.h file. It operates with ROI (see Regions of Interest in Intel IPP).

This function performs an image compositing operation on RGBA images using alpha values of both images. The compositing is done by overlaying pixels (r_A, g_A,b_A, α_A) from the foreground image pSrc1 with pixels (r_B,g_B,b_B, α_B) from the background image pSrc2 to produce pixels (r_C,g_C,b_C, α_C) in the resultant image pDst. The alpha values are assumed to be normalized to the range [0..1].

The type of the compositing operation is indicated by the alphaType parameter. Use Table “Possible Values of the Parameter alphaType” to choose a valid alphaType value depending on the required composition type. For example, the resulting pixel color components for the OVER operation (see Table “Types of Image Composing Operations”) are computed as follows:

r_C = α_A * r_A +(1 - α_A)* α_B *r_B

g_C = α_A * g_A +(1 - α_A)* α_B *g_B

b_C = α_A * b_A +(1 - α_A)* α_B *b_B

The resulting (normalized) alpha value is computed as

α_C = α_A +(1 - α_A)* α_B

This function can be used for unsigned pixel data only.

Return Values

ippStsNoErr	Indicates no error. Any other value indicates an error or a warning.
ippStsNullPtrErr	Indicates an error condition if one of the specified pointers is NULL.
ippStsSizeErr	Indicates an error condition if roiSize has a field with zero or negative value.