The next image is rendered using OpenCL. With approx. 1 million samples per pixel, the reflection inside the cooper sphere is refined.
Using GPU acceleration gain significant rendering performance improvement. The above GPU render image took approx. half hour to render 1.1 million samples, while the top image, the CPU took about 9 hours to render 65536 samples. This is a brief summary for GPU render analysis, I will give more details later.