// create image and load external data
imgSrc = vgCreateImage(VG_lRGBA_8888, imgGirlAlphaWidth, imgGirlAlphaHeight, VG_IMAGE_QUALITY_NONANTIALIASED);
vgImageSubData(imgSrc, (const void *)imgGirlAlphaData, imgGirlAlphaDataStride, imgGirlAlphaFormat, 0, 0, imgGirlAlphaWidth, imgGirlAlphaHeight);
imgDst = vgCreateImage(VG_lRGBA_8888, imgGirlAlphaWidth, imgGirlAlphaHeight, VG_IMAGE_QUALITY_NONANTIALIASED);

// create a desaturate matrix
s = 0.5f;
colMatrix[0] = 0.213f + 0.787f * s;  colMatrix[4] = 0.715f - 0.715f * s;  colMatrix[8]  = 0.072f - 0.072f * s;  colMatrix[12] = 0.0f;   colMatrix[16] = 0.0f;
colMatrix[1] = 0.213f - 0.213f * s;  colMatrix[5] = 0.715f + 0.285f * s;  colMatrix[9]  = 0.072f - 0.072f * s;  colMatrix[13] = 0.0f;   colMatrix[17] = 0.0f;
colMatrix[2] = 0.213f - 0.213f * s;  colMatrix[6] = 0.715f - 0.715f * s;  colMatrix[10] = 0.072f + 0.928f * s;  colMatrix[14] = 0.0f;   colMatrix[18] = 0.0f;
colMatrix[3] = 0.0f;                 colMatrix[7] = 0.0f;                 colMatrix[11] = 0.0f;                 colMatrix[15] = 1.0f;   colMatrix[19] = 0.0f;

vgSeti(VG_FILTER_CHANNEL_MASK, VG_RED | VG_GREEN | VG_BLUE | VG_ALPHA);

// apply filter in linear unpremultiplied color space
vgSeti(VG_FILTER_FORMAT_LINEAR, VG_TRUE);
vgSeti(VG_FILTER_FORMAT_PREMULTIPLIED, VG_FALSE);
vgColorMatrix(imgDst, imgSrc, colMatrix);
vgGetImageSubData(imgDst, imgOutputDataRGBA, imgGirlAlphaDataStride, imgGirlAlphaFormat, 0, 0, imgGirlAlphaWidth, imgGirlAlphaHeight);
strcpy(imgFileName, "filter_colormatrix_l.png");
saveImage32(f, imgFileName, "Apply desaturate filter in linear unpremultiplied color space.", imgGirlAlphaWidth, imgGirlAlphaHeight, imgOutputDataRGBA, 0);

// apply desaturate filter in linear premultiplied color space
vgSeti(VG_FILTER_FORMAT_LINEAR, VG_TRUE);
vgSeti(VG_FILTER_FORMAT_PREMULTIPLIED, VG_TRUE);
vgColorMatrix(imgDst, imgSrc, colMatrix);
vgGetImageSubData(imgDst, imgOutputDataRGBA, imgGirlAlphaDataStride, imgGirlAlphaFormat, 0, 0, imgGirlAlphaWidth, imgGirlAlphaHeight);
strcpy(imgFileName, "filter_colormatrix_l_pre.png");
saveImage32(f, imgFileName, "Apply desaturate filter in linear premultiplied color space.", imgGirlAlphaWidth, imgGirlAlphaHeight, imgOutputDataRGBA, 0);

// apply desaturate filter in non-linear unpremultiplied color space
vgSeti(VG_FILTER_FORMAT_LINEAR, VG_FALSE);
vgSeti(VG_FILTER_FORMAT_PREMULTIPLIED, VG_FALSE);
vgColorMatrix(imgDst, imgSrc, colMatrix);
vgGetImageSubData(imgDst, imgOutputDataRGBA, imgGirlAlphaDataStride, imgGirlAlphaFormat, 0, 0, imgGirlAlphaWidth, imgGirlAlphaHeight);
strcpy(imgFileName, "filter_colormatrix_s.png");
saveImage32(f, imgFileName, "Apply desaturate filter in non-linear unpremultiplied color space.", imgGirlAlphaWidth, imgGirlAlphaHeight, imgOutputDataRGBA, 0);

// apply desaturate filter in non-linear premultiplied color space
vgSeti(VG_FILTER_FORMAT_LINEAR, VG_FALSE);
vgSeti(VG_FILTER_FORMAT_PREMULTIPLIED, VG_TRUE);
vgColorMatrix(imgDst, imgSrc, colMatrix);
vgGetImageSubData(imgDst, imgOutputDataRGBA, imgGirlAlphaDataStride, imgGirlAlphaFormat, 0, 0, imgGirlAlphaWidth, imgGirlAlphaHeight);
strcpy(imgFileName, "filter_colormatrix_s_pre.png");
saveImage32(f, imgFileName, "Apply desaturate filter in non-linear premultiplied color space.", imgGirlAlphaWidth, imgGirlAlphaHeight, imgOutputDataRGBA, 0);

vgDestroyImage(imgSrc);
vgDestroyImage(imgDst);