AlphaCompC

Combines two images using constant alpha values.

Syntax

IppStatus ippiAlphaCompC_<mod>(const Ipp<datatype>* pSrc1, int src1Step, Ipp<datatype> alpha1, const Ipp<datatype>* pSrc2, int src2Step, Ipp<datatype> alpha2, Ipp<datatype>* pDst, int dstStep, IppiSize roiSize, IppiAlphaType alphaType);

Supported values for mod:

8u_C1R	8u_C3R	8u_C4R	8u_AC4R
16u_C1R	16u_C3R	16u_C4R	16u_AC4R
8s_C1R
16s_C1R
32u_C1R
32s_C1R
32f_C1R

IppStatus ippiAlphaCompC_<mod>(const Ipp<datatype>* constpSrc1[4], int src1Step, Ipp<datatype> alpha1, const Ipp<datatype>* const pSrc2[4], int src2Step, Ipp<datatype> alpha2, 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.
alpha1, alpha2	Constant alpha values to use for the compositing operation.
alphaType	The composition type to perform. See Table “Possible Values of the Parameter alphaType” for the type value and description.

Description

The function ippiAlphaCompC 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 one-channel image buffers, three-channel RGB and four-channel RGBA image buffers and on planar images, using constant alpha values alpha1 and alpha2. These values are passed to the function as parameters.

The compositing is done by overlaying pixels from the foreground image ROI pSrc1 with pixels from the background image ROI pSrc2 to produce pixels in the resultant image ROI pDst. The alpha values are 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 = α₁ * r_A +(1 - α₁)* α₂ *r_B

g_C = α₁ * g_A +(1 - α₁)* α₂ *g_B

b_C = α₁ * b_A +(1 - α₁)* α₂ *b_B

where α₁, α₂ are the normalised alpha values alpha1, alpha2.

This function can be used for unsigned pixel data only.

Example “Using Alpha Composition Function” shows how to use alpha composition function.

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.

Using Alpha Composition Function

IppStatus acomp( void ) {
   Ipp8u imga[8*8], imgb[8*8], imgc[8*8];
   IppiSize roi = { 8, 8 };
   IppStatus st;
   ippiImageRamp_8u_C1R( imga, 8, roi, 0, 1, ippAxsHorizontal );
   ippiImageRamp_8u_C1R( imgb, 8, roi, 0, 2, ippAxsHorizontal );
   st = ippiAlphaCompC_8u_C1R( imga, 8, 255/3, imgb, 8, 255, imgc, 8, roi, ippAlphaOver );
   printf( "over: a=%d,A=255/3; b=%d,B=255; c=%d //
c=a*A+b*(1-A)*B\n",imga[6],imgb[6],imgc[6] );
   return st;
}

Output

over: a=6,A=255/3; b=12,B=255; c=10 // c=a*A+b*B*(1-A)