NVIDIA 2D Image And Signal Performance Primitives (NPP)  Version 11.2.0.*
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Functions

BGR to Lab color conversion. More...

Functions

NppStatus nppiBGRToLab_8u_C3R_Ctx (const Npp8u *pSrc, int nSrcStep, Npp8u *pDst, int nDstStep, NppiSize oSizeROI, NppStreamContext nppStreamCtx)
 3 channel 8-bit unsigned packed BGR to 3 channel 8-bit unsigned packed Lab color conversion. More...
 
NppStatus nppiBGRToLab_8u_C3R (const Npp8u *pSrc, int nSrcStep, Npp8u *pDst, int nDstStep, NppiSize oSizeROI)
 

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 
)
NppStatus nppiBGRToLab_8u_C3R_Ctx ( const Npp8u pSrc,
int  nSrcStep,
Npp8u pDst,
int  nDstStep,
NppiSize  oSizeROI,
NppStreamContext  nppStreamCtx 
)

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

Parameters
pSrcSource-Image Pointer.
nSrcStepSource-Image Line Step.
pDstDestination-Image Pointer.
nDstStepDestination-Image Line Step.
oSizeROIRegion-of-Interest (ROI).
nppStreamCtxApplication Managed Stream Context.
Returns
Image Data Related Error Codes, ROI Related Error Codes

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