LabToBGR

Converts a Lab image to the BGR color model.

Syntax

IppStatus ippiLabToBGR_8u_C3R(const Ipp8u* pSrc, int srcStep, Ipp8u* pDst, int dstStep, IppiSize roiSize);

IppStatus ippiLabToBGR_16u8u_C3R(const Ipp16u* pSrc, int srcStep, Ipp8u* pDst, int dstStep, IppiSize roiSize);

Parameters

pSrc	Pointer to the source image ROI.
srcStep	Distance in bytes between starts of consecutive lines in the source image.
pDst	Pointer to the destination image ROI.
dstStep	Distance in bytes between starts of consecutive lines in the destination image.
roiSize	Size of the source and destination ROI in pixels.

Description

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

This function converts the CIE Lab image pSrc to the BGR image pDst in two steps. First, the conversion is carried out into CIE XYZ format.

To accomplish it, Lab components are transformed back into their original range. This is done for different data types in the following way.

For 8u data type:

L = L * 100./255.

a = a - 128.

b = b - 128.

For 16u data type:

L = L * 100./65535.

a = (a/255. - 128.)

b = (b/255.) - 128.)

After that, conversion to XYZ format takes place as follows:

Y = Y_n* P^3.

X = X_n*(P + a/500.)^3.

Z = Z_n*(P - b/200.)^3.

where

P = (L +16)/116.

After this intermediate conversion is done, the obtained XYZ image is then converted to the destination BGR format using equations defined for the ippiXYZToRGB function.

Return Values

ippStsNoErr	Indicates no error. Any other value indicates an error.
ippStsNullPtrErr	Indicates an error condition if pSrc or pDst is NULL.
ippStsSizeErr	Indicates an error condition if roiSize has a field with a zero or negative value.