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Projector Contrast Ratio FAQ


New - Dynamic Iris - 3D Contrast Ratio

CON-trast Ratio (CR)  How black are the blacks?

Contrast Ratio Contrast Ratio

  The 7 gray bars are the same! 

The right hand image is the same as the left, less the black bars..

Above, only difference is how YOU perceived the brightness.

That's what we mean by "Real World" we don't get carried away with specifications that just add zeros onto last year's claims. 

Specifications often have little relationship to how people watch movies and TV etc. in conditions encountered in the Real World.

Real World Speed  Specifications are not always realistic  

Too cryptic?  

What we're saying above is the car can have a massive top speed if you use it in a way that's not recommended for normal driving.

Toyota don't say: Maximum speed is 50,000kph*
*Over a cliff (disregarding Terminal Velocity and Air Density).


Several home entertainment makers almost go that far with outrageous claims that only when you read the fine print would you realise you most lightly won't come anywhere near using that specification.

I just had an outing to the "Real" cinema (I can't remember the last time I went), my eyes were opened to the technical aspects of film in a way I've never noticed before. It's all good news for the home cinema market!

I've been testing a few projectors and watching HD-TV so I found myself doing a comparison between the projectors I've seen and the movie I was watching..

Real World Tests
Real World CR Testing

70mm movie film has a contrast ratio of 1000:1 (often referred to as Dynamic Range) when I was watching black scenes they weren't black, it looked to me like (as far as contrast goes) as if I was watching a 400:1 LCD projector, that is the black seemed about 5% grey.

Note the current crop of HD projectors claim well in excess of 10,000:1 much more than any source material you'll be watching!

Contrast perception is influenced by the surrounding brightness.

Brightness is the perception of measurable luminance.

Next we'll see one billion to one** (1,000,000,000:1) CR !!
Why not they are just numbers, which have little relationship to real world screening conditions.

The Contrast Ratio of a Digital Projector in a Classroom or Business Environment is Irrelevant - Epson

"You will notice that as soon as you add even a small amount of light to the room the difference between the two projectors becomes imperceptible. The human eye will not see a significant difference between 90:1 and 80:1 or 11:1 and 12:1."

There are two ways (3 if you count "Real World") to measure contrast ratio (CR) "ANSI" and "Full on/off" be sure your looking at the same type of measurement before making a decision based on numbers, for example the full on/off method will normally be at least 25% more than ANSI.

ANSI

ANSI CR Pattern

The ratio between the average brightness of 8 alternating white rectangles and the average brightness of another 8 alternating black rectangles.

The screen is divided into 4 x 4 rectangles, specified by ANSI. Also called "Checkerboard" it's a more realistic way to test a projector than On/Off but not favored because of marketing concerns.

AIM's testing

Full On/Off

The ratio between the center brightness of all white (Full On) image and the one of all black (Full Off) image. The contrast - Full On/Off is always larger than Contrast - ANSI.

Measurements must be made in a completely dark room. Many DLP models have their CR measured with the “white segment” of the color wheel turned on.

This increases the white measurements. Home theater users may turn the white segment (Presentation mode) off, many projectors turn it off automatically in video mode.

You can glean from the above that buying a projector for home theater based on On/Off CR specifications alone may not be a great idea, the ACTUAL usable contrast ratio you end up is lightly to be much lower.

Some DLP projectors and Iris controlled models seem to be leaving the way with deceptive advertising..


Dynamic Iris Contrast Ratio enhancement.

Overall it's a good idea but it fails when the whole scene does not warrant the same reduction in brightness. The iris in a projector works the same way as one in a camera except it's changing the amount of light from the projector's lamp.

In a really dark room watching a dark scene you don't need a lot of brightness as it can be counter productive. The iris closes in this case making the whole scene darker. If the iris could change on a per pixel basis it would be perfect.

Example (simulated) watching a video with windows; notice as the iris adjusts it changes the whole image.

No iris. Dynamic Iris simulation 

Iris open.

Note the rest of the image is brighter also.

Dynamic Iris simulation 

Iris closed. 

Note the rest of the image is darker than it should be.

Dynamic Iris simulation 

3D Contrast Ratio

We think the public are being misled unless it's made clear the limitation is the 3D active shutter glasses which are generally rated at 1,000:1 contrast ratio.

A chain is only as strong as the weakest link. In this case it's not even the glasses; it's our eyes (/brain) that thinks the two sections of gray are not the same in the image below.   EPSON 3D Glasses

Contrast Ratio illusion

They are the same shade of gray.


"Real World" Contrast Ratio

Any more and it's all for nothing CR.

Self explanatory really, use a real image and see what the projector can do with the ratio between the 100% black and 100% white points.

Sharpness

The movie was not as sharp as many HD-TV programs, I was looking at the faces, the grass, whatever was in focus and non of it came close to the sharpness of a good HD-TV program.

Artefacts

Much is made of "Rainbow effects" on DLP projectors, some people see them, many don't. I noticed numerous Artefacts in the movie, mostly "cigarette burns" as they are known in the trade, you know, the little specks that pop up every now and then. The larger the image the more you see.

Once you get over the wow factor of IMAX have a look at the quality..

Colour

I won't be so critical of projectors in future having noted scenes where the colour balance had shifted in the movie.

"Don't get all carried away with big contrast ratio numbers.."

Most projectors are rated in the 300/3000 to 1 contrast ratio, that is to say the blacks are 300 times darker than the white (on a 300:1 model), this means that true black may appear as grayish.

Projectors with say 1200:1 contrast ratio look more realistic showing dark subject matter than 300:1. Having said that the difference in performance is provided your room is totally free from light (vary rare) in the real world we have trouble justifying the price hike between a 1000:1 and a 3000:1 projector as the difference is not 3 times better, rather a slight difference that most people may not notice unless the room is dark.

An example of how manufactures try to bambusal you with CR.

Note the real Contrast Ratio (Native) as seen on a brochure before the creative department got their hands on it. It's rare to see such honesty these days, next thing you know someone will (has) claim 1,000,000:1 now we have up to 200,000:1 which is just plain stupid in our opinion.

Words like unbelievable, unprecedented and un-lightly fit well.

Truth about CR

Epson Brochure which if extrapolated out means 200,000:1
really means 8000:1 real CR at best.

1,000,000:1 -- It's a bit like saying your car will do 300kmh if you take out the seats, air conditioner, radio, carpets then drive it over a cliff. Not something you'd do every day.

A closer analogy would be measuring the dynamic range of your sound system with the volume, bass and treble all at +100% You'd never use that setting to listen with, any more that you'd use Dynamic mode to watch cinema in a dark room, it would look rubbish and kill your eyes! -- AIM

Home theater users tends to fall into two areas, the purist who would have a dedicated room that is totally light controlled and the rest of us who may have a projector in the lounge or family room, for the later spending big or worrying too much about contrast ratio is a waste of time and money as any light in the room and it's game over for contrast, in fact..

"The size of your projection room (how close the walls and ceiling are to the screen) plus the paint colour, carpets and fittings can change the ACTUAL contract ratio by at least a factor of five!"

Many people prefer to have some soft ambient lighting as it makes viewing easier on the eyes, i.e. the contrast ratio is not such a big deal.

If you turn off ALL lights and achieve total darkness you will see some white in the black, which is the point, how often will you be in a totally dark room?

Brightness is the most important thing in daylight
On a bright day or a room with a fair amount of light all the contrast ratio
and DPI in the world won't take the place of brightness or ANSI lumens.

Blacks can only be as black as projection screen is in the ambient light.

If your room is not pitch black the screen will be reflecting some light. The lighter the room the less you need worry about a high contrast ratio. If you were that fussy you would paint your walls black like the cinema.

New? Marketing Fodder

Claims that the marketing guru's are starting to make on some projectors are starting to remind me of the sham regarding scanners.

When we started selling desk top scanners (before Windows 3.1!) the normal DPI was 300 OPTICAL or actual, as luck would have it that's about the DPI a human eye can resolve.

Later we saw scanners with higher optical DPI which comes in handy for enlargements and scanning 35mm film (we would recommend a dedicated film scanner free from scanning through glass to avoid "Newton Rings") for the normal user 300 was still plenty, office documents are normally 200 DPI.

Next the manufacturers had an "Interpolation War" whereby 4800, 9600, 19200 DPI or more was printed on the box and naturally many punters wanted the highest number. Higher the better the scanner? No. But it sure makes the box with 19200 easier to sell than the box with 1200 DPI unless you know what you're talking about.

First point is interpolated DPI is fake and just a mathematical averaging of the dots and placing more dots in the spaces between the actual optical dots. You can do this in Photoshop etc. too. Normally of little use. "So you want 19200 DPI? You must have one of Nasa's space computers computers?" Did you know A4 colour scan at 19200DPI = 1GIG?? Are you sure you need that! Well no.. OK Let's talk about what you're using your scanner for!

Projectors claiming 6,000:1 to 10,000:1 in reality are under 1000:1 if you use "Real World" tests.

A few points to consider before getting carried away with contrast ratio:

(I'm not an ophthalmologist so feel free to do your own research, some will disagree with figures here, however from what I've seen watching people during demonstrations of home theatre systems, unless you're using specific test images most people can't notice as much difference as you'd expect in regard to contrast and actual projected pixels..)

• The eyes Contrast Sensitivity Function is around 300 for the average person, it is dependent on the spatial frequency or the gap between parts of the image that vary in contrast.

• In lower light conditions i.e. when LUX is halved, a doubling in image area is required to maintain the same contrast perception which means brighter images look like they have more contrast and a brighter projector with a lower CR may seem better than one with less ANSI Lumens (Lower LUX reading) but has a higher CR, especially in lit conditions. [See the graph below]

If the light output from the projector isn't higher than the room average LUX the image will look washed out as CR will count for little and ANSI Lumens are king.

Notice a CR of just 50:1 in a room with 25 LUX (=2 dinner candles) regardless of the projectors CR.
A dinner candle is about 12 LUX.
(LUX = The International System unit of illumination: one lumen uniformly distributed over an area of one square meter.)

• At low light levels contrast sensitivity of the eye is approximately 8% of maximum. Dark adaptation takes 25 minutes to reach 80 percent adaptation, an hour for full adaptation. (In other words the first hour of the movie is not your best in this CR battle)

This is why pilots (thinking of single engine light aircraft..) use red torches when flying of a night so in case of an emergency landing they have a chance too see where they are landing.

Looking at a bright white light kills your night vision. So looking at a bright scene in a movie doesn't help your eyes sensitivity to the next dark one! (Can you see where I'm going with this yet?)

• You can get a much better score or contrast perception by looking at static test patterns however as home cinema is normally of moving pictures this too can be misleading.

• Don't confuse dynamic range with contrast sensitivity, the eye has the highest dynamic range around better than any electronic gadget under ideal conditions you can see in bright sun light or moon light once your eyes adjust. Most digital cameras are useless in starlight.

• This doesn't mean that a projector with a CR of 2000:1 or more isn't better than one rated at 400:1 however the perceived advantage is a lot smaller than optimistic claims the manufacturers would have you believe. Note you must be viewing under ideal conditions to see the largest variance in contrast.

• Your Notebook PC is about 300:1 too.
• Cinema is 1000:1
• Any light in the room makes higher than say 400:1 contrast ratio academic.
• The loss of contrast sensitivity accelerates with age, at 60, the amount of light reaching the photoreceptors is only 33% of the amount seen at age 20. By the late seventies, the amount falls to 12%.

Contrast perception..

So what are we saying here?

Don't get all carried away with big contrast ratio numbers, your eye is the limiting factor, that and the amount of ambient light in the room. We haven't even touched on the source material.

The size of your projection room (how close the walls and ceiling are to the screen) plus the paint colour, carpets and fittings can change the ACTUAL contract ratio by at least a factor of five! I haven't yet seen a Home Theater room that didn't decrease the actual contrast ratio due to reflected light. Black walls, carpets and all.

FOR THE PURPOSE OF HOME CINEMA

What Contrast Ratio can we see?

Some say 100:1, 200:1 others talk of dynamic range..

•Many factors effect the eyes ability to Perceive contrast so on average.. when watching a movie using a projector with some reflected and/or ambient light in the room..
We say the eye can see an average 300:1 CR.

 

In summary it's our opinion that 2000:1 is fine for light controlled rooms and 400:1 for your family/living room or presentations.


References/Quotes:

http://cobalt056.bpe.es.osaka-u.ac.jp/ohzawa-lab/izumi/CSF/A_What_is_CSF.html
http://www.ergogero.com/pages/agingeye.html
http://webvision.med.utah.edu/KallSpatial.html#contrast
http://vision.bhs.mq.edu.au/~peterw/csf.html
http://www.bbriefings.com/pdf/886/lth041_t_siemens.pdf
http://www.hdtvexpert.com/pages/shmontrast.htm
http://preview.videosystems.com/display/video_fallacy_contrast/

Conclusions
So, just how much contrast do you need to see in an image? Empirical data suggests the human eye is limited to a dynamic range of 100:1 at any given instant. That means that if you look at a scene with objects of different luminance values, you won't be able to discern more than a 100:1 difference between the darkest and lightest objects. Of course, the instant your eye moves, its built-in auto-iris function raises and lowers the grayscale boundaries. That's what allows you to perceive shadow detail and also pick out a white cat scurrying along in a field of snow.

http://videosystems.primediabusiness.com/ar/video_fallacy_contrast/

"The human eye can perceive a contrast ratio of 800:1" http://www.betterphoto.com/article.asp?id=50

http://www.darksky.org/infoshts/is156.html

Contrast sensitivity shows a significant age-related decline (Ophthalmic Physiol Opt 2000;20:323-34).
Wavefront aberrations of the cornea also increase with age, leading to poor vision quality especially when the pupil dilates as in the dark

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=10962698&itool=iconabstr&query_hl=1


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