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Electronic Theatre Controls Inc

What Is Calibrated Direct Mode?

Overview and History

LED emitter manufacturing is an imprecise process, and the process results in emitters which vary from each other, sometimes significantly. Manufacturers sort emitters into "bins," which are groups of LEDs which fall within a specific color tolerance, measured in MacAdam Ellipses. This means that when a product is made using these emitters, knowing which bin the emitters are from lets a fixture manufacturer know where on the color spectrum a specific LED will fall, and how much intensity and color tolerance there is expected to be. Unfortunately, not every LED bin is available at all times, so when selecting emitters to be used in fixtures, multiple approved bins must be specified or fixtures would become unavailable to ship when a bin goes out of stock. The result of this is that the output of LED fixtures will vary based on the bins that were available when they were manufactured, and a manufacturer needs to have ways to compensate for that fact in order to have an acceptable product.

Original Selador LED fixtures had one control mode: 1 channel per color, directly controlled, plus intensity. The emitter boards were made using "recipes," or specific mixes of emitter bins based on what was available at the time the PCB was manufactured. When a batch of fixtures was ordered, they would be shipped with the same recipe so the fixtures in the system would match. If new fixtures needed to be added to the system, they would need to be ordered with the same recipe as the existing fixtures, otherwise there would be visible differences between the new and old units' output.

For Desire, Source Four LED, and ColorSource fixtures, ETC developed a method to calibrate the output of the emitters in a fixture during the manufacturing process. Instead of defining specific recipes of emitter bins, the fixture knows exactly where on the color spectrum its own emitters are, and how bright they can get. It can then use that information to compensate for these variances to meet a particular target color. Therefore, fixtures can be mixed, and regardless of when they were manufactured, they can match each other. However, this did not apply to direct mode, so if a designer wanted to have direct emitter control, they would need to manually match fixtures which may have different outputs due to emitter variance.

Calibrated Direct Mode

In Source Four LED Series 2 software 1.8.1 and greater, the Fos/4 line, Source Four LED Series 3, and the ColorSource V line, Direct mode uses calibration data to better match output between fixtures. However, to ensure the most granular control of the fixture possible, this is limited compared to the calibration applied to non-direct modes.

  • Calibrated Direct mode will allow you to directly control all emitters in a fixture, but it will compensate for its particular emitter intensity variations when more than one color is used at a time. It will not compensate for color variations, since doing so would require overriding the direct mix set by the user.
    • When only one color is output, the fixture will use the maximum brightness it can, so "pure" colors will be as bright as they were with original Direct mode.
  • Other modes will use the fixture's calibration data for both color and intensity to find the best LED mix for the target color set by the user.

As a result, even with modern fixtures, in Direct mode it is possible for multiple fixtures with emitters that do not match perfectly to have visible color differences when set to the same color mix. This is expected. In this case, a user will need to either use a fully-calibrated mode or manually adjust the color mix between fixtures to get their overall output to match.

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