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Home-Cinema Projector Screens Testing

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Home-Cinema Projector Screens

by Florian Friedrich on03/22/2010

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How we test projector screens

Minolta CS-2000 spectroradiometer

We use the Minolta CS-2000 spectroradiometer to test screens in our darkened test theatre.

Almost all home-cinema experts agree that the projector screen is one of the most important components of the modern home cinema. And, of course, almost all manufacturers claim that their screens produce totally neutral, contrast-rich images. This makes choosing the right product very difficult, since almost no home-cinema fans have the technological means to evaluate a screen’s quality properly.

Trying out various screens in your own four walls is theoretically possible, but in practice requires a great deal of effort, as well as excellent contacts with the various manufacturers. Alternatively, you can let us do the hard work, and base your decision on our in-depth reviews. So far, we’ve tested the following projector screens. Click on the links to read the individual reviews:

• DNP Supernova One
• Davision Cadre No.1
• Stewart Luxus Deluxe Screenwall FireHawk
• Stewart Luxus Deluxe Screenwall GrayHawk
• Stewart Luxus Deluxe Screenwall StudioTek
• Spalluto WS-OS Rollo 16:9
• Da-Lite JKP Affinity

Background Info

How can projector screens increase the picture’s contrast

It sounds illogical that a projector screen can actually increase the picture’s contrast. But that is, in fact, the case — and there are two good reasons why:

1. Eliminating scattered light from the surroundings
Very few rooms are so black that they reflect no light at all. As soon as a projector screen is illuminated and reflects diffuse light, it will, of course, also illuminate the room around it — just like when a torch shines on a piece of white paper. The problem is therefore this: The room is now bright, and the white screen will always look white, even in places where it’s actually supposed to be dark.

To bypass this problem, screen manufacturers Stewart Filmscreen and DNP have gone into their bag of magic tricks and found a clever solution to the problem: They combined a slightly darkened screen with a reflective layer, ultimately sending more of the light towards the viewer than a diffuse, white screen does. In addition to this, special materials and optical layers absorb light that arrives from the sides.

2. Optical trickery using masking
The principle is simple: A white screen always seems brighter if surrounded by a black region. The darker the screen’s masking, therefore, the greater the brightness and contrast appear.

Visual testing

the basic waveform is a characteristic of the projector

You can see clearly how the reflected colour spectrum differs at various viewing angles from -90 to +90 degrees. The basic waveform is a characteristic of the projector.

To allow us to make as accurate a judgement as possible, the test conditions must be correct. We used two high-end, Full HD projectors during our tests: the Samsung SP-A 800 B (reference colours) and the Pioneer Kuro KRF-9000 (reference contrast). We played back Blu-rays on Pioneer’s BDP-LX 70 A, and used the blockbuster “Enchanted” as a test film. This Blu-ray is excellently mastered and offers scenes of various types, which we used to evaluate the colour fidelity and detail in particular. We also used test patterns from the test disc “DVE HD Basics”. To eliminate external factors, we carried out the tests in a completely darkened room with black walls.

Measurements

The test conditions also included calibrating the projectors to match the D65 colour temperature exactly on a standard white surface — this would then allow us to evaluate each screen’s colour fidelity. We measured and recorded the degree to which this value varies as viewing angle increases — these measurements were carried out using a Minolta CS-2000 spectroradiometer, mounted on a motorized turntable with a rotational accuracy of 0.1 degrees. Using a spotlight (shining indirectly via a black wall) and two reflectors, we examined the influence of external light under controlled conditions. We measured the ANSI contrast directly on the screen — without reflectors — to derive reproducible measurements of the screen’s contrast capabilities.

The test field

Of course, besides testing the new generation of screens from Stewart Filmscreen, we also invited other manufacturers to put their screens to our test, giving them a chance to meet our quality criteria as closely as possible — with an emphasis on colour neutrality, picture uniformity, and suitability for 1080p. For this test, we selected the manufacturers that we found most promising.

Background Info

Projector-screen glossary

Blackdrop:
Blackdrop refers to the black area at the top of a screen. As a general rule: the more blackdrop, the better — it minimises reflections to the ceiling and allows variable positioning. Only present in roll-up screens.

Gain factor:
Gain expresses the brightness of a given area in relation to matt white. Magnesium carbonate is used to represent “standard” matt white surfaces, according to standards set down by the German Institute for Standardization (better known in the U.K. as “DIN”). We therefore use magnesium carbonate as a reference material for our measurements. Generally, small scattering angles are associated with a high gain factor.

Hotspot:
A small range of viewing angles at which the screen is noticeably brighter.

Indicatrix:
This is a diagram that shows how the luminance varies with viewing angle. Sharp peaks indicate a hotspot.

Masking:
The black area around the edge of the screen that encloses the actual picture area. This increases the subjective contrast and helps to conceal inactive areas of the picture (letterbox bars, for example). Masking is particularly beneficial when you’re using a variety of picture formats or digital keystone correction.

Viewing angle:
Indicates the angle from the normal at which the picture’s brightness measures half of the value in the centre (measured at 5 degrees).

Conclusion

During our tests, one thing became clear: If you’ve got a dark home cinema and a good 1080p projector, you should resist cutting any corners with the screen. Remember that the projector’s picture relies on the screen: In the ideal case, while it might not greatly improve the picture, it also won’t do it any harm — and that’s the crucial point. As is often the case, cheap solutions look exactly that — cheap — and fall short of the quality criteria required of a modern, high-definition home cinema.