BGRToLab

BGR to Lab color conversion. More...

Functions
NppStatus	nppiBGRToLab_8u_C3R (const Npp8u *pSrc, int nSrcStep, Npp8u *pDst, int nDstStep, NppiSize oSizeROI)
	3 channel 8-bit unsigned packed BGR to 3 channel 8-bit unsigned packed Lab color conversion. More...

Detailed Description

BGR to Lab color conversion.

This is how NPP converts gamma corrected BGR or RGB to Lab using the CIE Lab D65 white point with a Y luminance of 1.0. The computed values of the L component are in the range [0..100], a and b component values are in the range [-128..127]. The code uses cbrtf() the 32 bit floating point cube root math function.

*  // use CIE Lab chromaticity coordinates

*  #define nCIE_LAB_D65_xn 0.950455F
*  #define nCIE_LAB_D65_yn 1.0F
*  #define nCIE_LAB_D65_zn 1.088753F
*  // First convert to XYZ

*  Npp32f nNormalizedR = (Npp32f)R * 0.003921569F; // / 255.0F

*  Npp32f nNormalizedG = (Npp32f)G * 0.003921569F;
*  Npp32f nNormalizedB = (Npp32f)B * 0.003921569F;
*  Npp32f nX = 0.412453F * nNormalizedR + 0.35758F  * nNormalizedG + 0.180423F * nNormalizedB; 
*  Npp32f nY = 0.212671F * nNormalizedR + 0.71516F  * nNormalizedG + 0.072169F * nNormalizedB;
*  Npp32f nZ = 0.019334F * nNormalizedR + 0.119193F * nNormalizedG + 0.950227F * nNormalizedB;
*  Npp32f nL = cbrtf(nY);
*  Npp32f nA;
*  Npp32f nB;
*  Npp32f nfX = nX * 1.052128F; // / nCIE_LAB_D65_xn; 

*  Npp32f nfY = nY;
*  Npp32f nfZ = nZ * 0.918482F; // / nCIE_LAB_D65_zn;

*  nfY = nL - 16.0F;
*  nL = 116.0F * nL - 16.0F;
*  nA = cbrtf(nfX) - 16.0F;
*  nA = 500.0F * (nA - nfY);
*  nB = cbrtf(nfZ) - 16.0F;
*  nB = 200.0F * (nfY - nB);
*  // Now scale Lab range

*  nL = nL * 255.0F * 0.01F; // / 100.0F

*  nA = nA + 128.0F;
*  nB = nB + 128.0F;
*  L = (Npp8u)nL;
*  a = (Npp8u)nA;
*  b = (Npp8u)nB;
*  

Function Documentation

NppStatus nppiBGRToLab_8u_C3R	(	const Npp8u *	pSrc,
		int	nSrcStep,
		Npp8u *	pDst,
		int	nDstStep,
		NppiSize	oSizeROI
	)

3 channel 8-bit unsigned packed BGR to 3 channel 8-bit unsigned packed Lab color conversion.

Parameters

pSrc	Source-Image Pointer.
nSrcStep	Source-Image Line Step.
pDst	Destination-Image Pointer.
nDstStep	Destination-Image Line Step.
oSizeROI	Region-of-Interest (ROI).

Returns

Image Data Related Error Codes, ROI Related Error Codes