LED panels are only a part of what must be considered on a Virtual Production stage. When investing in VP it is vital to consider the type of camera used to ensure the best result. Today we’ll discuss different camera shutters - specifically rolling shutters and global shutters, and how these fit into VP.
To begin with, let's look at what exactly a rolling shutter is compared to a global shutter. The primary difference is that a rolling shutter camera’s sensor is exposed in a motion from top to bottom or bottom to top. In contrast, a global shutter’s sensor is wholly exposed at the same time, giving a singular, full capture of an image. Rolling shutters are susceptible to distortion when capturing high speeds, as the shutter can expose too slowly.
Here’s an example of how something like an engine’s propeller can look in a rolling shutter camera. This demonstrates how traditionally a global shutter has an advantage for high speed subjects.
Rolling and global shutters perform differently for VP. Global shutters are generally seen as ideal for use within LED volumes because the refresh rate of LED walls is extremely fast and we need to capture this without losing any data. An LED screen will typically draw each frame from top to bottom. If using a rolling shutter, it's possible that the camera could capture the screen midway through being drawn. The consequence of this is “screen tearing”, where an image has a noticeable dividing line where it has not updated, with half of the image a single frame behind.
That being said, rolling shutters are widely used - it’s simply a matter of making sure the shutter’s exposure time is synchronised with the refresh rate of the screen using a genlock signal sent to the wall and the camera. A rolling shutter may also be preferable if price has a lot of influence in the decision making process, due to the comparatively high cost of the sensors in cameras with a global shutter.
At Target3D we currently work with cameras with both types of shutter. We have invested in Red’s Komodos (global shutter) and Blackmagic’s 12k Ursas (rolling shutter), with the former being used at Target3D’s Virtual Production Test Stage. Having the flexibility of both shutter types is useful when adapting to different shooting conditions and client requirements.
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