Among all the video projector specifications with which consumers must wrestle, the image contrast ratio is the least important. It is not, however, irrelevant since there are minimum ratios that should be considered (around 5000:1 or greater).
The image contrast ratio is the ratio between the brightest white and blackest black that the projection system can produce. Caveat emptor: not all contrast ratios are measured the same way.
So, what are the things consumers need to know? Here, we break down the facets of the issue of contrast ratios and provide our recommendations. Maintaining a proper contrast ratio for enjoyable viewing consists of three components: ratio, room, and screen.
In short, it is all about how the ratio was measured, in what type of viewing environment the projector will be used, and what quality projection surface will be used.
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Measuring Contrast Ratios
Many video projection system manufacturers employ clever marketing tactics to enhance the salability of their products. Among these are “creative” means of establishing contrast ratios. Most contrast ratios that are promoted are actually dynamic ratios.
Dynamic ratios are calculated by the brightest white under maximum illumination from the projector, compared against the darkest black under the lowest illumination setting of the machine. These ratios artificially inflate the actual performance of the projector under fixed illumination conditions.
True contrast ratio output measurements are actually performed using an industry-established protocol by the American National Standards Institute (ANSI): ANSI Contrast according to the 1998 protocol ANSI IT7.227.
This means of establishing the projection system contrast ratio uses a fixed image under conditions covered in our article “ANSI Lumens vs Lumens: What is the difference?” By this method, all measurements are performed under standardized conditions to provide a true measure of the white to the black ratio that a viewer would actually experience.
Most common video projection systems report a 5000:1 contrast ratio, however, machines with contrast ratios as small as 1000:1 and as high as 50000:1 are available in the consumer market. Some manufacturers openly state that their reported contrast ratios are dynamic ratios.
Unless specifically stated as an ANSI Contrast measurement, it is safe to assume that any reported values are dynamically obtained through illumination output changes and are therefore inflated. Noting this market issue, a reported contrast ratio of 5000:1 is the recommended target for most use environments.
The Prepared Viewing Environment
Although this article is all about contrast ratios, other elements of the equation bear mentioning. Just as a high-performance sports car will underperform if fed the incorrect grade of gasoline or shoed with poor quality tires, so a video projection system will disappoint the user if other crucial factors are not attended. These include where and how the system will be used.
A prepared viewing environment is a must for proper projector performance. Light contamination from ambient sources (power strips, LEDs) or window coverings (translucent curtains or blinds, loosely arranged blackout curtains), even minor amounts, can have potentially detrimental effects on image contrast.
Light contamination problems in the viewing environment will drop the performance of even an expensive video projection system to double-digit ratio values.
Shut off LED light sources or at least cover them. If power strips in the room are necessary, choose models with no switch or without an illuminated rocker switch.
Here are a few models with non-illuminated rocker switches that would serve the purpose: NTONPOWER 4-Outlet Electrical Surge Protector, NTONPOWER 4 Outlets 5 USB Desktop Charging Station, 3000W Power Strip Surge Protector with USB Ports by LineDear.
If you choose to use a room with windows, invest in some blackout curtains or blackout blinds. There are highly-rated and rather affordable options out there, such as these curtains by Nicetown, these curtains by Ryb Home, these blinds by Keego, or these window covers by Oxdigi.
We recommend a combined window treatment for an optimal viewing experience by combining blackout window blinds with blackout curtains. If the appearance of the curtains clashes with your décor, mount a second rod and place some more-attractive curtains on the outside.
Also, most blackout curtains are grommeted and are threaded onto the curtain rod, so a colorful second curtain could be overlaid on the blackout curtains.
And Don’t Forget the Screen…
The screen is the third component of proper video image contrast. Without a good viewing surface, all the contrast ratio voodoo in the world will not matter.
There are a variety of excellent video projection screens on the market. Which one you should select is highly dependent on the type of viewing environment you intend.
The classic choice is a white screen. Your typical white screen has a gain of 1.0 (1.0 Lambert). Essentially, this means you have near 100% diffuse reflectance (“matte”) from the screen when an image is projected on it (for example).
If you have a near-perfect viewing environment, such as an actual movie theater or a fastidiously prepared home theater room with no ambient light pollution, this type of screen will provide the best image contrast the projector can muster. If you require additional gain, such as 1.4 gain ratio or higher (for example), the amount of reflected light will be enhanced, albeit less diffusely and in a narrower viewing area.
Whereas this is not ideal for most home theater situations, high-gain screens are often appropriate for boardrooms where the audience is sitting in a closer space and the screen gain boost is necessary to overcome less-than-ideal lighting conditions.
A popular solution for viewing conditions with some ambient light problems is the use of grey projection screens, which operate at 0.8-0.9 gain (for example). Since video projectors cannot display black, but simply do not project light through those pixels, any ambient light in a room with a white screen will reflect light in those “black” spots and give a grey appearance, thus reducing projected contrast.
Grey screens tend to form a compromise between the reduced reflection of the ambient room light in black portions of the screen image and make black tones seem deeper. However, this compromise also diminishes the brightness of the white tones in the image due to the reduced screen gain. Despite this shortcoming, grey screens are the choice for most serious home theater set-ups.
Remember where we talked at length above about the importance of a prepared viewing environment for a proper image contrast ratio? Well, that applies to traditional screen materials. How about a black screen? Sounds crazy, right? Not so.
Recent developments by Screen Innovations, Inc., a company out of Austin, Texas, produces black video projection screens that they claim can be used in any environment apart from trying to watch movies on the surface of the sun. Their black screens reflect negligible ambient light and only reflect light that is directly projected on them.
The result is stunning (see this). Black blacks, bright highlights, even under normal conference room lights-up conditions. It is truly impressive and likely the future of projection screen technology.
Their screens stare at prices similar to other quality projection screens, although presently these screens may be out of the affordability range of most home theater enthusiasts. Screen Innovation has resellers all across the USA and abroad; see their website for details.
To Sum It Up
Regardless of the video projection system, you choose to purchase, a few minimum considerations should be undertaken. The first consideration is selecting a system with a contrast ratio of around 5000:1 for starters.
The second consideration is a proper viewing environment where ambient light is reduced as much as possible or practicable. The third consideration is the selection of a screen to preserve the projected contrast ratio, a matter of viewing environment and intended use.