OpenCV (Emgu.CV) — compositing images with alpha

Question

I\'m using Emgu.CV to perform some basic image manipulation and composition. My images are loaded as Image.

Question #1:

Answer 1

You'll have to iterate through each pixel. I'm assuming image 1 is the frog image, and image 2 is the city image, with image1 always being bigger than image2.

//to simulate image1.AddInPlace(image2)
 int image2w = image2.Width;
 int image2h = image2.Height;
 int i,j;
 var alpha;
 for (i = 0; i < w; i++)
 {
     for (j = 0; j < h; j++)
     {
           //alpha=255 is opaque > image2 should be used
           alpha = image2[3][j,i].Intensity;
           image1[j, i] 
               = new Bgra(
               image2[j, i].Blue * alpha + (image1[j, i].Blue * (255-alpha)),
               image2[j, i].Green * alpha + (image1[j, i].Green * (255-alpha)),
               image2[j, i].Red * alpha + (image1[j, i].Red * (255-alpha)));
      }
 }