Just as resolution continues to increase on HDTV sets, so it seems does contrast ratio. I few years ago, digital displays were exclaiming how impressive a 1,000:1 contrast ratio was. Now 10,000:1 is not that uncommon. And since contrast ratio is more important to resolution in the production of a great picture, it sounds like these new displays should be amazingly fantastic. Unfortunately, these extremely high contrast ratios have little to do with real world performance and are, to a great extent, marketing hype.
First of all, it's necessary to understand the difference between the two types of contrast ratio measurements. The one used by pretty much every manufacturer out there is full on (100% white) / full off (100% black). While this can give some amazingly high numbers, people don't watch all-white or all-black screens. Comparing the brightest whites in one scene to the blackest blacks in another scene is not representative of the picture quality available at the exact instance the viewer is watching each scene. (Measuring the screens at 2 different times also allows further manipulation of the display between tests, such as switching to a different color wheel setting, changing the aperture of an iris, or taking the measurement at a more favorable location on the screen.)
The contrast ratio that matters most for the most common viewing scenarios is ANSI contrast ratio [1]. With ANSI contrast ratio, the black and white levels are measured at the same time on the same screen using a 16-square black and white checkerboard image. What this means is that it is representative of the contrast ratio achievable at any one point in time; this is what is really important to viewers. [Edit: see AlenK's comment below regarding situations where On/Off contrast ratio become important.]
The reason ANSI contrast ratios are not published is because of marketing. ANSI contrast ratios are much lower than on/off contrast ratios. An ANSI contrast ratio of 250:1 would be an impressive result and 600:1 would be outstanding — but much too low of a number if casually compared to an on/off contrast ratio of 6,000:1.
This info is for front projection and does not directly relate to flat panels:
One last point that is critical is the impact ambient light has on perceived contrast ratio. Ambient light kills contrast ratio on any and every display. If you make out the beige carpet below your flat panel, your contrast ratio is being negatively impacted. If there is 1 lux of ambient light in the room (i.e. a small candle), the max perceivable contrast ratio is 500:1. A dimly lighted room with 30 lux of lighting would squash the maximum perceivable contrast ratio to 50:1 [2]. Unless you have a completely dark room covered in black velvet, you'll never be able to perceive the high on/off contrast ratios claimed by manufacturers — those numbers are meaningless otherwise.
Conclusion: If you're looking to buy a new HDTV, don't place much merit on the contrast ratio published by the manufacturer; it is pretty much meaningless for real-world (a little bit of light in the room) viewing. Plus, I've never seen a review of a calibrated display meet or exceed the manufacturer published contrast ratios. Look for independent test results that measure both ANSI and On/Off contrast ratio on a properly-calibrated display. If you are always watching TV in a well-lit room, the contrast ratio doesn't really matter anyway; display brightness is more important the brighter the room is. But if you like to enjoy the full performance of your display by turning the lights off, high contrast ratio is extremely important.
If you're considering a model for which no reviews listing ANSI and On/Off contrast ratio exist, use this rule of thumb:
- CRT displays are pretty much the king of on/off contrast and give the best black levels, have great color reproduction, but lower ANSI contrast ratios [edited 2007-05-29]
- Plasmas offer almost the same (and often better) on/off contrast ratio performance as compared to CRT and can offer better ANSI contrast ratios.
- DLP is the best for digital front/rear projection displays
- LCoS (aka SXRD, DiLA) are very close to DLP
- LCD (both flat panels and front/rear projection) offers the poorest contrast ratios (especially on/off); however, they can be among the brightest flat panels and that makes them great for bright rooms where it is difficult to perceive contrast ratio.
Like always, there are some exceptions. Always look at a display yourself before you purchase it. LCD flat panels have great bang-for-the buck and look pretty good on a bright show-room floor. See if you can view and compare it in your normal viewing environment (a completely dark room, a very bright room) before you make your final decision. Plasmas have great black levels but are terrible for glare and reflection off the glass front screen; plasma + direct sunlight = unwatchable combination.
I have never liked a single LCD TV picture… Ever. It is the Emperor with No Clothes, in that when someone shows me their newest $4000+ prize, it is virtually impossible to say, "You have been suckered, your TV sucks."
Aside from projection, the 36" tube is my favorite for viewing.
From what I understand, the newest plasmas can meet or even exceed CRT contrast ratios. The models that Pioneer will release in mid-2007 are supposedly the best displays ever made; their current plasmas are awesome as is. Here is a link: http://www.twice.com/article/CA6405089.html?nid=2402
Carlton,
Thanks for the site. Great info.
The link you posted in the comment is just a Pioneer press release. It's a good teaser, but so far just Pioneer's word. We'll need to wait for independent tests (like the ones you mentioned) to verify the claims.
Good article, Carlton.
Great site, Carlton, and this blog entry a nice attempt to educate about contrast ratios. But, you shouldn't dismiss on/off contrast ratio so easily. Both numbers are important. While people don't watch all black or all white screens, the average picture level for a lot of video content is fairly low (some movies more so than others). For that kind of material, poor on/off is immediately obvious (assuming a low ambient level in the environment). Poor ANSI generally has less of a negative affect. And these two figures of merit are nearly independent – it is easily possible to achieve a good number for one and a poor number for the other (either way).
Second, CRT projectors are the "kings" of on/off contrast ratio, not ANSI. Their ANSI ratios are actually relatively poor, although rarely were the numbers ever published. A model with air-coupled lenses would be typically 50:1, a liquid-coupled model maybe as high as 200:1. In comparison, ANSI contrast for a well-designed DLP projector (for instance) is typically over 400:1. Yet there is no question that CRT projectors, even air-coupled ones, produce subjectively "punchy" pictures with good contrast.
Please take my comments as constructive criticism, based on over 20 years as a display engineer designing projectors (starting with those antiquated CRT models!).
Good point, AlenK, about on/off contrast. Many movies have low-light scenes.
Carlton said CRT/Plasma has the best contrast for displays, DLP for projection. Do you disagree?
I'm curious why CRT projection has poor ANSI contrast compared to DLP. If it is due to the lens system, how is the DPL lens system able to do better?
CRTs, whether direct view or projection, still have among the highest on/off contrast ratios, but Plasma (see Pioneer announcement at CES) and even direct-view LCD (see Sharp 1,000,000:1 on/off CR prototype) are catching up. Among non-CRT projection displays, JVC's current 1080p HD-DILA front-projection models currently hold top spot: 15,000:1 on/off without dynamic control. But TI demo'd a 100,000:1 rear-projection display (presumably with dynamic control) at CES, so the game of leap-frog and specmanship continues.
Projection CRT has low ANSI CR, even with liquid coupling, because of this: The CRT phosphor emits light in an essentially lambertian pattern (i.e., diffusely). Some light from a high brightness feature will thus reflect from wherever the refractive index changes (glass-to-air-to-glass = a lot of reflection, glass-to-liquid-to-glass = less but not zero reflection) at a severe angle and illuminate some other part of the phosphor.
In the case of a micro-display, be it based on DLP, LCD or LCoS, light from the lamp is focused onto the panel, arriving from a far more limited cone of angles. The light which transmits through or is reflected off is thus much more efficiently captured by the lens – not as much of it is bouncing off at odd angles. There is still some, and there are still reflections within the lens itself because of all the glass-to-different-glass and air-to-glass interfaces, so it's not perfect. But it can be much, much better. (Note that anti-reflection coatings are typically used in both cases.)
AlenK: Thanks for your great comments. I updated the original post to correct/clarify some of the mistakes you noted.
One other thing: You say "I've never seen a review of a calibrated display meet or exceed the manufacturer published contrast ratios."
Here's at least one: Greg Rogers' review of JVC's DLA-RS1U in Widescreen Review, Issue 120, May 2007. I quote: "In the Normal lamp power mode, the RS1 produced 595 lumens, which is equivalent to 27.2 fL (foot-Lamberts) from my 1.3 gain screen, with an extraordinary 16,400:1 full-field (on-off) contrast ratio." JVC's spec is 15,000:1.
There have been other displays reviewed in WSR by Greg Rogers that meet or exceed their published CR's. Greg knows how to calibrate and measure displays properly and he's no stooge for the manufacturers.
Pretty good information in general….. but:
That may be true if the otherwise black area of the TV reflected 100% of this ambient light source (which it obviously does not) thus the contrast does not deteriorate NEARLY as fast as the above quote would have you believe.
To put that in perspective, pretend you have a white surface / screen and are using a projector mounted behind you.
In a dark room, the contrast is going to be pretty average, like you would expect from a movie theater.
add ambient light (a candle or otherwise) and the contrast will suffer fast, just as mentioned above in the quote.
HOWEVER
Nearly every screen in existence will filter or absorb / re-direct that light, thus maintaining a good percentage of the original ratio.
Think about it… 30lux leaves you only a 50:1 ratio??? Typical room lighting could provide over 1000lux…. do you honestly think in that condition your only getting about 2:1 contrast ratio? common with a front projector maybe!
Andy: Very good point; those contrast ratio numbers are for front projection (white screens) which much higher ambient light reflection. The black screen of a flat panel would be impacted much less. I'm not sure what the equation is to calculate the exact impact, but it would be interesting to compare the difference. I've updated the post to reflect this info.
So after all the extensive research you have all conducted on the HDTV's, for Joe Consumer; which is the best CRT, LCD, Plasma tv's "currently" on the market. In other words, if you were going out to your local electronic store, no special order items, which tv's would you buy today?
I think that the samsung dlp's with the led engine is a great option. And apparenty getting better and better. I have read a few bad reviews and dont get where they are comming from. I bought a hlt-6189sx in late 2007, most of the bad reviews where from earlier in the year so maybe those issues were fixed? All I know is my one buddy has the jvc dila 61" close to same specs(10,000:1, 1080p, etc) but my led engine is so much brighter and the colors are extremely vivid and accurate in comparision. with DLP you get the fastest response times, longest life before deterioration, low power, sharpest picture and absolutely no visible picture structure. (the LED's are icing on the cake)
This is all fine and very educational. However I am now more confused than ever as there are NO t.v.'s that offer all of the "good stuf" within one unit. Gentlemen what is the bottom line?
It is absolutely true that there is no perfect TV. The bottom line it to consider your viewing environment and trust your eyes. Most people want a thin flat panel TV, so that means LCD or Plasma. If your room is extremely bright with lots of windows, a matte finish screen on an LCD is probably your best option; a LCD with a LED backlight instead of the traditional florescent backlight is best if you're willing to pay the extra price. If your room is fairly dark with few windows, plasma will provide a stunning picture with deep blacks, very fast refresh rates, but slightly less brightness overall. Understand your criteria and then go look at some models. Don't be afraid to turn them off so you can more easily detect screen glare.