RGBToLUV

Syntax

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

This function converts the RGB image pSrc to the CIE LUV CIE LUV image pDst in two steps. First, the conversion is done into CIE XYZ format, using equations defined for the ippiRGBToXYZ function. After that, conversion to LUV image is performed in accordance with the following equations:

L = 116. * (Y/Y_n)^1/3. - 16.

U = 13. * L * (u - u_n)

V = 13. * L * (v - v_n)

where

u = 4.*X / (X + 15.*Y + 3.*Z)

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

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.

The computed values of the L component are in the range [0..100], U component in the range [-134..220], and V component in the range [-140..122].

The equations above are given on the assumption that R, G, and B values are normalized to the range [0..1]. In case of the floating-point data type, the input RGB values must already be in the range [0..1]. For integer data types, normalization is done by the conversion function internally.

In case of 8u data type, the computed L, U, and V values are quantized and converted to fit in the range [0..IPP_MAX_8U] as follows:

L = L * IPP_MAX_8U / 100.

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

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

In case of 16u data type, the computed L, U, and V values are quantized and converted to fit in the range [0..IPP_MAX_16U] as follows:

L = L * IPP_MAX_16U / 100.

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

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

In case of 16s data type, the computed L,U, and V values are quantized and converted to fit in the range [IPP_MIN_16S..IPP_MAX_16S] as follows:

L = L * IPP_MAX_16U / 100. + IPP_MIN_16S

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

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

For 32f data type, no further conversion is done and L, U, and V components remain in the ranges [0..100], [-134..220], and [-140..122], respectively.

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.