I saved the main render elements as 16-bit PNG files, and rendered the assist channels like AO, mask, shadow, etc. Now it was time to start the post-processing.
I used Photoshop to composite this work, where I mainly used layer blending modes and made local adjustments. Masking and adjustment layers are your good friends at times like these.
The sky is the most important part of this work. I used two high resolution panorama parts to composite the sky, using different masks in different layers to get a good result (Fig.53 - 54).
Then I added the ground and car (Fig.55).
Compositing car paint was another important part. Besides Curves or Level tools, reflection and specular channels are good tools to adjust car paint. For example, using Softlight or Overlay to composite the specular channel will increase the structure's construct, and using the refract channel will make the car's lights more beautiful (Fig.56).
Now I needed to do something to make the sky better. To create the sun, I used two glare textures to create the sun's glare. One was powerful and the other weak, so I could adjust the halo and temperature accurately (Fig.57).
Using a mountain texture to create the distant mountains, I paid attention to the blur effect. With decreased saturation, I got a "fog" effect (Fig.58).
To get a better result, I used another layer to adjust the details of the sky carefully (Fig.59).
I added more layers, carefully adjusting the image, until I had the final results and SLS AMG was done (Fig.60).
As this wasn't a commercial piece of work, I had a lot of time to test different skills and techniques. I think personal works are a great way of improving your skills, because you have the time and energy to get everything perfect!
Finally, thanks for the help from my brother Fei; he gave me many suggestions and a lot of help.