LUVToRGB

Converts a LUV image to the RGB color model.

Syntax

IppStatus ippiLUVToRGB_<mod>(const Ipp<datatype>* pSrc, int srcStep, Ipp<datatype>* pDst, int dstStep, IppiSize roiSize);

Supported values for mod:

8u_C3R	16u_C3R	16s_C3R	32f_C3R
8u_AC4R	16u_AC4R	16s_AC4R	32f_AC4R

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

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

To accomplish it, LUV 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./ IPP_MAX_8U

U = (U * 354./ IPP_MAX_8U) - 134.

V = (V * 262./ IPP_MAX_8U) - 140.

For 16u data type:

L = L * 100./ IPP_MAX_16U

U = (U * 354./ IPP_MAX_16U) - 134.

V = (V * 262./ IPP_MAX_16U) - 140.

For 16s data type:

L = (L - IPP_MIN_16S)* 100./ IPP_MAX_16U

U = ((U - IPP_MIN_16S)* 354./ IPP_MAX_16U) - 134.

V = ((V - IPP_MIN_16S) * 262./ IPP_MAX_16U) - 140.

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

Y = Y_n * ((L + 16.) / 116.)**3.

X = -9.* Y * u / ((u - 4.)* v - u* v )

Z = (9.* Y - 15*v*Y - v*X) / 3. * v

where

u = U / (13.* L) + u_n

v = V / (13.* L) + v_n

and

u_n = 4.*x_n / (-2.*x_n + 12.*y_n + 3.)

v_n = 9.*y_n / (-2.*x_n + 12.*y_n + 3.)

Here x_n = 0.312713, y_n = 0.329016 are the CIE chromaticity coordinates of the D65 white point, and Y_n = 1.0 is the luminance of the D65 white point.

After this intermediate conversion is done, the obtained XYZ image is then converted to the destination RGB 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.