For a while now, we’ve been looking at the technology in an audio, video and lighting system. We’ve gone through a good bit of the AVL signal chain so far. We’ve looked at live capture and play sources, as well audio and video processing. Now, we’re looking at lighting processing, an important step in LED video systems.
In an LED video system, video inputs are converted and sent to creative LED video installations. These installations incorporate multiple LED video products, including video strips, dots and panels of various shapes. Each individual LED on each of these products represents a single pixel in a video image. The different LED video products come together to create a single LED video system. The LED Video processing step takes the pixels from the video source and matches them to the correct individual LEDs in the LED Video system. A lot of complex processing goes into this seemingly-simple step, so let’s take a closer look at how it works.
Video Input and Processing
Processing is performed in an LED video signal processing unit like the Martin P3 System Controller. Video enters the controller using a video format such as DVI or SDI. As I mentioned last time, the P3 controller has built in video scaling, and thus can accept any standard video resolution up to 1080p. The video processor in the P3 controller also has an image processor, and can adjust elements such as brightness, contrast, low light and gamma. As well, the video processor has zoom and crop capabilities, allowing the lighting designer to zoom the video into the desired area of interest. Because the video processor is built into the P3 system, there is no need for separate video scaler, lowering complexity in the signal chain and reducing latency.
Mapping Fixtures on the Campus
Once the signal has gone through video processing, the lighting processing can begin. The procedure starts with the designer creating a show file. A new canvas is created, and the lighting designer sets the size of the canvas to match the real-world dimensions (length and width) of the LED video installation. This is important, as all of the other processing that goes on within the P3 system is adjusted to match the size of the show canvas.
Once the show file is created, the system designer places the various LED video products onto the video image as they are to be laid out physically on the stage, building façade, etc. The P3 controller then ensures each LED video product gets the correct part of the image (that is, the correct set of pixels from the video). All of the processing and adjustment to accomplish this is performed within the P3 controller.
For example, when an LED video fixture is rotated as part of the installation, the lighting designer simply lays the fixture at an angle as part of the mapping process in the P3 software. The P3 Processor automatically rotates the video opposite of how the fixture is rotated before it sends the video to the fixture. If the fixture is to be rotated 45° to the right, the P3 system rotates the video 45° to the left. When the fixture is then rotated 45° to the right while it is installed, the video will play as straight up and down the way it should. Again, all of this is done automatically within the P3 software.
Another example of this automatic adjustment is compensating for installations that mix products of multiple pixel pitches in the same video installation. Pixel pitch refers to the amount of space between each individual LED. Devices with a lower pixel pitch can display more “pixels” per inch than products with a higher pixel pitch, and thus provide more visual detail when viewing both products from the same distance. Lower pixel pitch products provide more detail, but are more expensive.
Often times, a lighting designer may choose to have products of different pixel pitches within the same installation. In these cases, the P3 system will account for these differences automatically. If, for example, the system has both 10mm pixel pitch products and 20mm pixel pitch products, and you send the same video to both sets of products, the same video would be twice as large on the 20mm fixtures. To prevent this, the P3 system automatically pre-scales the video for each product as appropriate for the canvas size the designer set when the project began. That way, the video will look completely consistent with the same size across all the products.
Color Processing in the LED Fixtures
Like many of HARMAN’s audio and video processing solutions, the processing within P3 is technically a “distributed processing” architecture, where part of the processing is performed within the various devices in the system. In this case, color temperature and color space adjustments are made within the individual LED video fixtures, though these settings are still fully controlled by the P3 software.
The color temperature of the specific video product can be adjusted based upon the needs of the installation. This allows lighting designers to have the right white mix for the application. For example, applications like theater can adjust the color temperature, so that instead of a cool white of around 6500 Kelvin, the fixtures use a more pleasing and warmer white of around 3200 Kelvin.
LED video fixtures can also adjust the entire color space, which controls color saturation of the red, green and blue light on the fixture. This is useful in broadcast, where sometimes LED video colors are too saturated, causing problems for broadcast cameras. With color space adjustment, lighting designers in a broadcast installation can tone down the saturation of the color space so that LED video products on a stage or set look better on camera.
Real-Time Control from the Lighting Desk
For creative applications, parameters of the LED Video processing can be adjusted from a lighting console using DMX or Art-Net. This allows the lighting designer to control the brightness and intensity of all the fixtures in real time. For example, if a particular “look” using moving heads within the lighting system calls for warm colors, the lighting designer can adjust the warmth of the video signal to match using the lighting console. The lighting designer can also blackout both moving heads and LED video products at the same time using the lighting console.
Martin LED video fixtures can also be used as true LED lighting products, with the lighting console taking over and controlling the fixtures directly. This allows the lighting designer to setting the color of the fixtures directly for certain songs or looks, while still using them as video products at other times.
Do you have experience designing using LED video processing? Share you experiences in the comments.