For some time now we have been recommending that you ignore contrast specifications when shopping for a projector. Why ignore contrast specs you wonder? Well, simple. They are the most worthless, misleading, uninformative spec on the sheet, that's why. They don't tell you much about what you should expect to see on the screen, and they certainly don't tell you anything about how one model will compare to another.
Now, lest anyone jump to erroneous conclusions, I am not suggesting that vendors are publishing distorted specs that are intended to deceive. Far from it. In fact, many of the published specs seem to be reasonably accurate as far as they go. But even if all contrast specifications were perfectly accurate, they would still be pretty much worthless.
Why are contrast specs worthless?
Several reasons. First, contrast on projectors is not measured on an "apples to apples" basis. Some projectors have dynamic irises that open and close depending on the average light level in a given scene. Some have dynamically changing lumen output of the lamps. Some projectors have color wheels with white segments that can be turned off when black is displayed. Other projectors don't have these features. These operational differences mean that the contrast ratings are influenced by a lot of unstated variables. Of course, they might be accurate as applied to each particular projector's mode of operation, but they tend to be meaningless as points of comparison between models.
Second, excellent gray scale performance is at least as important, if not more important, than contrast in delivering great picture quality. Imagine you had a projector with a contrast rating of a million to one, but all it could do was show deep black and brilliant white without being very good at distinguishing subtle shades of gray. You'd have the deepest, richest black level ever, which is what a lot of people think of as the key to home theater Nirvana. But you'd still end up with a terrible picture, and you'd surely never know it from the contrast spec.
Third, even beyond the problem of getting apples-to-apples contrast ratings, and not having a clue about gray scale performance, there is a much bigger issue: Your ultimate perception of contrast on the screen is not determined solely by the inherent contrast potential of the projector. Unless you have a totally black room, your perception of contrast will be influenced by reflected light in the room, any ambient light in the room, and by the lumen output of the projector. By reflected light, I mean the light that bounces off the screen onto white ceilings and light colored carpets and furnishings, and back onto the screen.
In addition to light reflected and bounced from the screen, most people have ambient light in the room as well. This is light from any other source than the projector's lens. That could be lamps, track lighting, windows that cannot be blocked, status lights on the equipment in your rack, light leaks from the projector's vents, etc. Once this type of light becomes part of the equation, and it doesn't take much, actual contrast ratios on the screen drop to a mere fraction of the projector's potential.
Your viewing room. The hypothetical "ideal" viewing room for a front projection system would be totally black. It would be covered wall to wall and floor to ceiling in black, non-reflective fabric. All furnishings and drapes would be black. And if you had this type of viewing room, the contrast ratings on projectors might be relevant to some degree once you sorted out the differences in how they were being measured.
In practice, nobody has a pitch black viewing room covered in black, non-reflective fabric. For one, there is no such thing-even black velvet reflects some light; if it didn't, you wouldn't be able to see it, or to detect any substance or texture in it. Furthermore, nobody we know would buy a projector if you needed a pitch black room to get an enjoyable picture anyway. Certainly, people who are quite serious about large screen home theater will take reasonable steps to darken a dedicated theater room, using darker fabrics and wall paints. But even in this type of room you can end up with enough light bouncing around to compromise the contrast potential of the projector. And the fact is, most people don't want to install room-darkening features at all. They want to use their multi-purpose room for things other than movie viewing in the dark, so they retain friendlier, lighter colored walls and furnishings. In this type of room, you can still get a great picture, but the contrast rating of the projector has less to do with it than you might imagine.
Lumen output. If you've got light in the viewing room the easiest way to overcome the problem is to use a projector with higher lumen output. It might seem counterintuitive at first, but a bright projector with a comparatively low contrast rating can often produce an image that appears to be higher in contrast than a projector with an extremely high contrast rating, but lower brightness. This is because the light in the room often defines the minimum black level on the screen, while the lumen output of the projector determines the brightness of the highlights. In this situation, the projector's lumen output, not its contrast ratio, is mostly responsible for the actual range between black and white you see on the screen.
The effect of brightness on perceived contrast is easy to see just by moving a projector closer to the screen and shrinking the image size. As the projector's light is concentrated on a smaller area, the highlights get more brilliant while black levels, relatively speaking, stay about the same. The projector is not inherently any higher in contrast, but the image appears to be higher in contrast because there is an expansion of the luminance range between black and white. When light in the viewing room determines the level of black, the way you get a higher contrast image is to make the highlights brighter.
Now, there is a limit to this. Using a super bright projector in a dark room will give you eyestrain and a headache after a while. A rapid transition from a dark night scene to bright daylight scene can produce a jarring change in light energy on the screen that is distracting if not painful. Some people are more light sensitive than others, so there is no ideal or correct lumen output to compensate for any given level of reflected light. But if 400 ANSI lumens is a good amount of light for a 120" screen in a dark room, then 600 to 1000 lumens would be satisfying for most people in a room with a modest amount of ambient light. Ultimately, it is a matter of personal taste-finding that level of picture brightness that looks engaging and comfortable to you is the real objective.
Now that we have considered how misleading contrast specs can be, let's look at how they are generated, and how to interpret them.
Two Methods of Contrast Measurement
There are two commonly used methods of measuring contrast. One is called Full On/Off and the other is the ANSI contrast method. Full On/Off measures (a) the brightness of a white, 100 IRE test pattern ("full on"), and (b) the amount of brightness on a black, 0 IRE test pattern (full off), and expresses the two measurements as a ratio of white to black. A contrast ratio of 1,000:1 indicates that the meter is reading the white as being one thousand times brighter than the black.
The ANSI contrast measurement uses a checkerboard pattern of 16 rectangles, eight white and eight black. The brightness values of all the white squares are measured and averaged, and the brightness of the black squares are measured and averaged. The ratio of the averaged white readings to the black readings is the ANSI contrast ratio.
Where projectors are concerned, the Full On/Off and ANSI methods yield radically different numbers, and the ANSI reading is always substantially lower (not even in the same ballpark, actually). The reason is that, though we usually get similar readings between the white 100 IRE test pattern and the white rectangles on the checkerboard pattern, the black readings on the ANSI checkerboard are always higher than black readings on a full black 0 IRE test pattern.
Why is that? Well, first, there is always the potential for some light scatter in the light engine and projection lens when anything other than black is being projected. When the projector is displaying a fully black image, there is no light to scatter internally which could compromise the black level. When the checkerboard is being displayed, there is quite a bit of light being projected. A little bit of that light gets bounced around inside the lens or light engine and ends up compromising the black levels on the screen.
In addition, any dust that happens to be floating in the path of projected light will cause light scatter. And the low level of reflected light even from very black fabric in the test environment will affect black levels on the screen.
For example, let's say our meter tells us that "full on" white is 150 units and "full off" black is 0.05 units. That would be a contrast ratio of 3,000:1. Now we measure the ANSI checkerboard, and we still get 150 units on the whites, but we get 0.5 units on the blacks. The contrast ratio just dropped to 300:1 with a relatively subtle change in black level. And this is a change to black level that would be imperceptible to the human eye except in very dark environment. It is a change to black that would be neutralized by any reflected light in the room. When seen in these terms, the difference between 3,000:1 and 300:1 contrast doesn't seem like the enormous gap that the numbers themselves would suggest.
Factoring in the Projector's Operational Characteristics
To further complicate the contrast issue, we must also bear in mind that many projectors adjust their light output based on the average light level in a given scene. They can do this by adjusting the lamp power on the fly, or by opening and closing a variable iris, or by turning off a white segment in a color wheel. So when a dark scene is being projected, lumen output can be curtailed to make the black look blacker. Then when a bright scene comes along, lumen output will be returned to full power in order to achieve a more brilliant image. On the latest projectors that have these features, these adjustments to lumen output happen so quickly that the viewer rarely notices them.
It is important to recognize that with projectors that operate in this manner, the Full On/Off specification measures the projector's potential dynamic range from scene to scene, that is, comparing the deepest black in a dark scene to the brightest white in a bright scene. It does not measure the actual contrast within a given frame.
This is where the ANSI contrast method comes in handy. Since the ANSI method uses a single frame of rectangles that is 50% white and 50% black, it eliminates the projector's ability to vary lumen output from the equation. This is another reason why ANSI contrast numbers tend to be far lower than Full On/Off measurements. But just as the Full On/Off method does not tell the whole story, neither does the ANSI method.
A truly accurate measurement of ANSI contrast requires that we have our theoretical black room, with all walls, carpets, ceilings, furnishing, etc., totally black and non-reflective. In this pure black space, a projector might measure an ANSI contrast of, say, 600:1. However, if we do nothing more than introduce a white ceiling into our black room, the reflected light from the ceiling will cause ANSI contrast on the screen to plummet to 100:1 or less. So in real life usage, ANSI contrast performance is hammered by the presence of any reflective surface in the viewing environment. The extreme sensitivity of ANSI contrast specifications to the viewing environment cannot be understated, since the user will never experience such thing as a pure black, non-reflective room.
ProjectorCentral's Contrast Measurements
We have constructed a black tunnel for the purpose of taking contrast measurements. However, even the black velveteen fabric we used to line the tunnel is reflective to some degree. Our tunnel therefore replicates a very dark, but not perfectly black and nonreflective viewing space. Accordingly, our measurements will always be lower than the theoretical maximums quoted in vendor specifications. They are more likely to approximate what you'd actually achieve in fully darkened dedicated theater room.
Thus, when we quote contrast measurements we have taken, we must be careful to emphasize that our readings are dependent upon the test environment we use to measure them. Our contrast measurements on any given projector can only be used in comparison to other readings on projectors we have measured in our tunnel under the exact same conditions. Any attempt to compare our measurements to those published by vendors or anyone else is entirely invalid.
By the way, Full On/Off measurements are not nearly as sensitive to environmental conditions as are ANSI measurements. That is because the Full On/Off black level is measured on a fully black 0 IRE test pattern, so there is very little reflected light from the screen to influence the end result. Nevertheless, small differences between absolute black and almost absolute black are measured in just a few thousandths of a foot-lambert, and even rounding errors in the meter or small light leaks from the projector's vents can have a noticeable impact on the final numbers.
JVC DLA-RS2. The DLA-RS2 has an official Full On/Off specification of 30,000:1. What is not obvious from the spec is that the RS2 has no auto-iris or other feature to vary lumen output based on the average light level in the scene. Thus, the published specification is based on materially different operating conditions than projectors with variable lumen output capabilities like the Epson Cinema 1080 UB (rated at 50,000:1), and the Sony VPL-VW60 (rated at 35,000:1). Though the RS2's published rating is lower than these competitors, its actual native contrast performance is quite a bit higher. Without the irises active, Epson claims a native contrast of 4,000:1, and Sony claims 7,000:1. So in both cases the auto iris has a huge impact on the contrast numbers.
We measured the RS2's Full On/Off at 13,300:1, which is quite a bit lower than the official spec. Nevertheless, this is the highest native contrast reading we've measured from the projectors we've tested thus far. On the other hand, the RS2 measured 209:1 ANSI contrast, which is the lowest ANSI reading we have found among the high performance 1080p models we've tested.
BenQ W20000. The BenQ W20000 has a Full On/Off contrast spec of 20,000:1, including a variable iris. Our Full On/Off measurement was 8,800:1. So as with the RS2, our measurement was quite a bit lower than the official specification.
Meanwhile, our ANSI contrast measurement on the W20000 was 560:1, which is more than double that of the JVC RS2. It is noteworthy that the W20000 is a DLP projector. We have measured two other DLP projectors thus far with similar results. The Optoma HD80 registered an ANSI contrast reading of 515:1, and the new Infocus IN83 measured 517:1. However, not all DLP projectors manifest high ANSI readings. The Optoma HD65, a lower priced and lower performance DLP projector, measured 268:1.
In addition to the models noted previously, we have also tested the Viewsonic Pro8100, a new LCD 1080p model. That unit delivered an ANSI contrast reading of 258:1, and the Epson Cinema 1080 UB registered an ANSI reading of 255:1.
Thus, from the data we have collected so far it is evident that some of the high performance projectors incorporating DLP technology are delivering ANSI contrast readings in the low to mid-500's as compared to the LCD and LCOS competition which are measuring in the low to mid-200's. On the other hand, JVC's D-ILA based RS2 measures higher native contrast than any DLP product we've seen, and the Epson 1080 UB registers a dynamic contrast with iris active of 27,000:1. That is the highest number we've seen under any type of measurement on any unit.
The problem now becomes obvious. How is the bewildered consumer to interpret this conflicting data? Are you better off with higher native contrast, or higher ANSI contrast if you have to choose one over the other? How much benefit is gained from the use of auto irises to achieve extremely high dynamic contrast ratios, and to what degree do they influence your perception of real on-screen contrast? How does the room environment factor into it? What about lumen output? Etc., etc.
With the exception of a few high-end vendors, the industry does not publish ANSI contrast specifications since they are extremely low numbers compared to Full On/Off. The average consumer would not be expected to understand the differences. But the fact is that after the consumer has been conditioned to seeing Full On/Off ratings of 10,000:1 and up, even very good ANSI readings in the 500:1 range will sound anemic in comparison-they simply have no marketing sizzle. Perhaps it is just as well.
What does it all mean?
At the beginning of this article I said we were recommending that folks ignore contrast specs. By now I hope it is clear why. No single spec tells the whole story, whether it is Full On/Off or ANSI. And whatever half-truth any given spec may contain, it is lost in the practical reality of reflected light in the viewing room, ambient light in the room, and the very real compensating effects of the projector's lumen output. Beyond all this, a projector's ability to reproduce an even grayscale is also a major factor in the image's ultimate quality, and the contrast spec tells you nothing about a projector's abilities in this regard. The Samsung SP-A800B is an example of a beautiful projector with outstanding gray scale performance that nevertheless may not get as much attention as it deserves due to its relatively low (by competitive standards) 10,000:1 contrast spec. This illustrates the unfortunate downside to publishing contrast numbers-they often rivet the consumer's attention on a performance factor that is ultimately of marginal consequence.
In the end, good contrast is a vital component of image quality. But it is the real contrast you perceive on the screen that is vital, not the theoretical specs. You can influence your real contrast results by darkening your viewing room, by choosing a projector with a good range of lumen output, and/or by limiting the screen size you choose. These are major factors which determine how much contrast you will actually see in your projected image, and they have nothing to do with the contrast spec.
