电影里的街道为什么比现实中好看？

Why do movie sets always spray water on the ground when filming outside shots?
电影片场拍外景时为什么总要在地上洒水？

获得1.4m好评的回答@Pat Roberts：

WARNING : AFTER READING THIS A LITTLE BIT OF MOVIE MAGIC WILL BE GONE FOR YOU. YOU’LL NOTICE THIS FAKE EFFECT ALL THE TIME - EVEN ON BRIGHT SUNNY DAYS.
警告：读完这篇文章后，对你来说电影的某些魅力会消失，你总会注意到这个伪造出的效果——甚至在阳光明媚的天气也会注意到。
It’s called a wet-down:
这被称作 wet-down：

Excluding where it’s used to make it look like it it has rained:
那些为营造下雨效果而进行的洒水除外：
Daytime wet-down: Increased color saturation and contrast. Basically, it looks better.
白天洒水：提高色彩饱和度和对比度，主要就是视觉效果更好。
I can’t find a good before-and-after comparison, but you can do this yourself in your yard. Spray the plants and ground. The green will be more saturated and the dirt and rocks and bark will go darker and more saturated, leading to higher contrast.
我找不到好的洒水前后对比图，但你可以在自家院子试试，在植物和地面都洒上水，绿色会更绿，泥土、岩石和树皮颜色变得更暗，颜色更纯，对比度也更高。

Nighttime wet-down: It looks prettier, plus it makes asphalt show up better. If you have a matte black street it just looks like a black or grey background. If it’s wet it’ll reflect light and make the street surface more visible.
夜间洒水：夜景更美，而且沥青看起来效果更好。哑光的黑色街道看起来像黑色或灰色的背景，如果街道是湿的就会反光，使街道表面更显眼。