AlphaBlend Performance issues

[HowToExpect]

inline long long getCurrentTimeMicro()
{
    return std::chrono::duration_cast<std::chrono::microseconds>(std::chrono::steady_clock::now().time_since_epoch()).count();
}

static void InnerMixtureImage(IplImage* pSrc, IplImage* pDst, int xpos, int ypos)
{
    if (!pSrc || !pDst)
        return;

    if (pSrc->nChannels != 4 || pDst->nChannels != 4)
        return;

    int w = xpos + pSrc->width;
    int h = ypos + pSrc->height;

    if (w > pDst->width || h > pDst->height)
    {
        printf("<WARNING> %s: src width = %d, height = %d, dst width = %d, height = %d, pos x = %d, y = %d\r\n",
            __FUNCTION__, pSrc->width, pSrc->height, pDst->width, pDst->height, xpos, ypos);
        return;
    }

    int i, j;
    for (j = 0; j < pSrc->height; ++j)
    {

        unsigned char* pucDst = (unsigned char*)pDst->imageData + (j + ypos) * pDst->widthStep + xpos * pDst->nChannels;
        unsigned char* pucSrc = (unsigned char*)pSrc->imageData + j * pSrc->widthStep;

        for (i = 0; i < pSrc->width; ++i)
        {
            unsigned char alpha = pucSrc[3];

            if (alpha == 0)
            {
            }
            else if (alpha == 255)
            {
                pucDst[0] = pucSrc[0];
                pucDst[1] = pucSrc[1];
                pucDst[2] = pucSrc[2];
                pucDst[3] = pucSrc[3];
            }
            else 
            {
                pucDst[0] = (pucDst[0] * (255 - alpha) + pucSrc[0] * alpha) >> 8;
                pucDst[1] = (pucDst[1] * (255 - alpha) + pucSrc[1] * alpha) >> 8;
                pucDst[2] = (pucDst[2] * (255 - alpha) + pucSrc[2] * alpha) >> 8;
                pucDst[3] = pucDst[3] > alpha ? pucDst[3] : alpha;
            }
            pucDst += 4;
            pucSrc += 4;
        }
    }

}

int main()
{
    IplImage* pUpdate = cvLoadImage("update.png", CV_LOAD_IMAGE_UNCHANGED);

    int width = pUpdate->width;
    int height = pUpdate->height;

    IplImage* pImg = cvCreateImage(cvSize(width, height), 8, 4);
    cvSet(pImg, cvScalar(51, 51, 51, 255));

    IplImage* pChannel1 = cvCreateImage(cvGetSize(pUpdate), 8, 1);
    IplImage* pChannel2 = cvCreateImage(cvGetSize(pUpdate), 8, 1);
    IplImage* pChannel3 = cvCreateImage(cvGetSize(pUpdate), 8, 1);
    IplImage* pChannel4 = cvCreateImage(cvGetSize(pUpdate), 8, 1);

    cvSplit(pUpdate, pChannel1, pChannel2, pChannel3, pChannel4);

    int64_t start = getCurrentTimeMicro();

    Avx2::AlphaBlending((const uint8_t*)pUpdate->imageData, pUpdate->widthStep, pUpdate->width, pUpdate->height, pUpdate->nChannels,
                      (const uint8_t*)pChannel4->imageData, pChannel4->widthStep, (uint8_t*)pImg->imageData, pImg->widthStep);

    //InnerMixtureImage(pUpdate, pImg, 0, 0);
    int64_t end = getCurrentTimeMicro();

    cout << "elapsed time = " << (end - start) << " us " << endl;
}

[HowToExpect]

[HowToExpect]

use Avx2::AlphaBlending elapsed is 5000us, usr InnerMixtureImage elapsed is 3000us

[ermig1979]

Hello!

1) I would not recommend to call function Avx2::AlphaBlending direct. This is not part of Simd Library API. You have to use function SimdAlphaBlending. 2) You can test performance of this function with using of 'Test' application. For example:

./Test -fi=AlphaBlending -w=1920 -h=1080 -fe=Uniform

The result shows that using of AVX2 gives significant performance gain compare to Base code.

--------------------------------------------------------------------------------------------
| Function         |   API  Base  Sse2 Sse41  Avx2 | Bs/S2 Bs/S4 Bs/A2 | Bs/S2 S2/S4 S4/A2 |
--------------------------------------------------------------------------------------------
| Common, ms       | 0.522 3.205 1.084 0.721 0.522 |  2.96  4.45  6.14 |  2.96  1.50  1.38 |
--------------------------------------------------------------------------------------------
| AlphaBlending[1] | 0.215 1.338 0.305 0.299 0.214 |  4.38  4.47  6.27 |  4.38  1.02  1.40 |
| AlphaBlending[2] | 0.476 2.730 0.647 0.660 0.477 |  4.22  4.14  5.72 |  4.22  0.98  1.38 |
| AlphaBlending[3] | 0.704 5.091 4.984 0.971 0.718 |  1.02  5.24  7.09 |  1.02  5.13  1.35 |
| AlphaBlending[4] | 1.029 5.677 1.403 1.408 1.019 |  4.05  4.03  5.57 |  4.05  1.00  1.38 |
--------------------------------------------------------------------------------------------