If there’s one thing you can say, it's that High Dynamic Range (HDR) is currently a hot topic.
In a previous article we already described that there's currently no agreement or standardization of the definition of “high”. We also elaborated on how there is a law of diminishing returns at play (impacted a.o. by ambient parameters) that makes it ridiculous to have a race towards ever-increasing contrast ratios.
In this article we’ll go deeper into the internal, technological consequences and complexity of adding more contrast:
- How can you upgrade an existing projector?
- What does it take to develop a new projector with higher contrast ratio?
The optical path
Let’s start by explaining that the projector contrast ratio (but also brightness, uniformity, sharpness, …) is the end result of what is commonly called the optical path inside the system. Note that the end result as seen on screen is also affected by ambient parameters, but we will keep these out of scope for this article. The optical path is made up of different components, both optical and mechanical (read our dedicated whitepaper for more info on the optical path). The optical path is designed to guide the light within a certain “container”, quantified by the F-number or étendue. The specification of this container is one of the key contributors to the end value (out of the lens) of the projector contrast ratio.
Going to higher contrast ratios means adapting the optical path. When starting from an existing design, it is in practice only feasible to adapt a limited number of components. Typically these are the mechanical components, such as apertures. Doing more radical changes to the optical path creates conflicts with the available space (housing): sizes of lenses and other optical components scale very strongly with design parameters like F-number. When designing a new product, it is possible to take into account all components in the optical path, but the potential consequences are similar to the upgrade case. The graph below shows this:
When we start from the industry standard (2000:1 contrast ratio in cinema), we see that laser projection already exceeds this. Barco’s DP4K-L series yield a contrast ratio of 2500:1 which is 25% more than the existing industry standard. The question is: how much further can you take it? The effect that we see is that first gains can be achieved with limited impact on the total complexity/efficiency/cost: the blue curve is steep on its left side. Note that it is not 100% vertical: you’ll have to compromise something, be it brightness, size,… Then we see that adding more contrast is technically possible, but the compromises become increasingly higher: the blue curve flattens out as it goes to the right. At a certain point on the curve, you have to ask yourself: is going further really worth it? This is not a pure technical questions, but one to be answered by the industry as a whole.
Declining system efficiency
What we see happening in parallel in cinema projection is that the system efficiency goes down (the green curve). Laser projectors have a total system efficiency (lm/W) that significantly outperforms lamp-based projectors. The positive contribution to the total cost of ownership (TCO) is one of the major drivers for laser adoption. Since you cannot compromise on brightness (screen sizes stay the same) and only partially on system size (booths were designed with a certain available space), system efficiency is the factor that's going down. This curve has a different shape: efficiency losses are small when adding some contrast ratio, but drop quickly when going to higher values. At a certain point you reach levels far below the industry standard, where laser has a negative impact on TCO. Again you need to ask yourself: how much is enough?
Join the discussion
Barco is currently investigating, testing and validating the exact shape of these curves. We are collaborating and aligning with industry partners on what is feasible, realistic and acceptable. An - open - industry dialog on this topic is the best way forward to land this topic so that everyone can reap its benefits.
Feel free to join the discussion!
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