Here are some tips for using digital backgrounds with your green screen.
What a green screen allows you to do is put whatever you want in the background of a scene. When the scene shot in front of the green screen is put into post-production, the green part can be removed and a digital background can be put there in its place. There are a lot of standard digital backgrounds for green screen available that will mimic real world locations, or create something new entirely. Here are a few tips for how to select digital backgrounds for green screen use.
When selecting a digital background for green screen replacement you will want something that is going to blend approximately well with the scene that was shot ahead of time. This means that the character of the image should match the general character of the way that the video was capture, both in terms of the action in front of the lens and the image quality. For example, if the color patterns of the objects in the digital background do not match the subjects in front of that background then it is going to be difficult for the audience to suspend disbelief and accept that they are actually in that location. If you have a digital background for green screen replacement that you want to use, yet has a different image quality that your video, then you will want to alter it before employing it in your compositing during post-production.
Still images are not always the best to use as digital backgrounds for green screen compositing, and video is going to end up fitting much more accurately since it will appear as the real world. The motion in the video image is going to be critical for the consistency of the video, but at the same time excessive motion will not match the action in front of the camera. The best rule of thumb to follow is to have a video background that was filmed with a stationary camera that has a location with obvious movement, but movement that is relatively slow. For example, a setting in a park with shrubbery that is moving slightly with the wind. If there are quickly moving objects off in the distance then it will usually be alright, but if there is too much interaction close to the camera then the digital background will not match the foreground action. If you want the video background to maintain an incredible amount of motion you are going to have to make sure that you block the foreground action around the movement of the background to be composited in later.
What's most important to note about the green screen is that you cannot expect more than it has the ability to deliver. The green screen rarely looks as though it was filmed in the real world, though it can give great style to your video. Audiences will accept a reasonable compositing in the green screen even if it is not perfect, so do not expect that it is going to be the same as though you filmed it in a given locale. Lifting this expectation will allow you to really open up to the creative possibilities around the green screen.