what is different between use pointer to access chanel in row or use CvScalar

IplImage *Image=cvCreateImage(cvSize(640,500),IPL_DEPTH_32F,3);
for(int row=0; row<50; row++ )
{
    for(int col=0; col<Image->width; col++ ) {
        ((double *)(Image->imageData + row*Image->widthStep))[col*Image->nChannels + 0]=175;
        ((double *)(Image->imageData + row*Image->widthStep))[col*Image->nChannels + 1]=0;
        ((double *)(Image->imageData + row*Image->widthStep))[col*Image->nChannels + 2]=0;
    }
}
cvNamedWindow("A",0);
cvShowImage("A",Image);
cvWaitKey(0)

IplImage *Image=cvCreateImage(cvSize(640,500),IPL_DEPTH_32F,3);

CvScalar Sca;
Sca.val[0]=175;
Sca.val[1]=0;
Sca.val[2]=0;
for(int row=0; row<50; row++ )
{
    for(int col=0; col<Image->width; col++ )
    {
        cvSet2D(Image,row,col,Sca);
    }
}
cvNamedWindow("A",0);
cvShowImage("A",Image);
cvWaitKey(0);