CurtPalme.com Home Theater Forum

[km987654]

What determines contrast ratio. If you look at the projectos specs (Barco in this case) you will see there are several projectors that share the same tube and have the same lens type but have a different contrast ratio. So what determines contrast ratio if not the tube type??

[WanMan]

My god, you didn't a) Google or , b) Wiki this?

[WanMan]

CR can be measured in a variety of manners. In the context of THIS forum it is the Full On/Off Contrast Ratio. Measure how much light you get with full-field, non-blooming white. Record the value (X). Measure how much light you get with full-field, non-crushing black. Record the value (Y). X/Y is the Contrast Ratio.

[km987654]

OK so thats how you measure but why should two PJs with the same tube and LC tanks have different contrast ratio?? Why shouldn't they be the same?

[chillman]

Different HVPS for example.

[k.berger]

but then... as far as I understand, properly set-up CRT goes to TOTAL BLACK (measuring NO OUTPUT) at full black - 0 IRE signal level? Then CR would be always INFINITY? This has bugged me before...

Kris

[perisoft]

[k.berger]

You are right of course, I didn't think of real life environment (like those LEDs ). Actually when you use video level signal, it would be even less - only 1/235 only... Amazing that such crude scale can produce so wonderfully amazing image! I guess our eyes/brain combination is relatively easy to fool into seeing/believing this kind of illusion. Goes for the ears/brain too... .

[km987654]

[Mr. Green]

There must be something. I have only my eyes to tell me though. Without any other lights on, in a dark scene my LCD is bright enough for me to walk around stuff, my plasma is the same. Only with the CRT projector do I have to stop in my tracks and wait for a brighter scene before proceeding.

My plasma is supposedly 10,000:1, my LCD TV is 15,000:1 and my CRT projector is also 15,000:1. I'll tell you the LCD TV is no more than charcoal grey. The plasma is much better but still dark grey and the CRT is pretty much black. It can produce better black levels than anything else I've ever seen. Sure it's whites aren't as bright by a long shot, but if it is simply a measure of the distance between the two then the measurement is flawed. The plasma is way brighter than the LCD too. Having compared the 3 (by eye) the plasma should win hands down even though it has the lowest ratio, but it's pure white is way brighter than the other 2, but nothing compares to the film like blacks of the CRT. I don't believe the numbers at all. Just for fun, there was that Epson projector I compared the CRT to and that boasted 50,000:1. Not even remotely close to black, but tons brighter. Yes, I know it was the (after fooling your brain ratio), but it was the number advertised. If it really isn't that high, then it is BS, that they are claiming. My projector was easily twice as black with a quarter of the supposed contrast ratio. No wonder people get sucked into buying digital POS's.

I almost think they need to scrap contrast ratio and give values for brightness and black levels (absence of light). We want to know "how inky black can it go?" That would give a much more accurate measurement. I want to know that when there is a fade to black you might as well be in a mine shaft without a lantern! I know I'm no tech and techies will argue. I only know the number I'm given and how it fares to other displays in my house. Based on the "contrast ratio" I have no information because I associate "blacks" with contrast ratio. If I can't use that to buy a display then what else can we use?

[km987654]

[perisoft]

CRT Contrast Ratio = 10,000 + MSRP / 2

[Spanky Ham]

Wan explained on/off cr. The other one is ANSI cr, which is measuring a white square on a black background. Since the white can wash out the black, you get a much lower number than on/off. CRTs are bad at ANSI while DLP is really good. Without getting to technical, ANSI matters in the bright scenes.

As for the figures quoted by the manufacturers of CRT pjs, flat panels, or any other video device, they are usually pure fiction. Most CRTs can be calibrated to achieve very high on/off crs. I believe Darin measured a G70 at a couple of hundred thousand to one. I think Art did the same with his G90s as well. The problem is making sure you don't crush the low end gamma with this set up. Person99 used to say that CRTs could not do the high on/off without crushing blacks. I am not sure if this applies with the gamma corrected devices.

Most of the specs listed should be taken with a grain of salt. Bruce mentioned this recently about the Best/Worst list. TSE has said on more than one occasion that most of those bandwidth specs were marketing BS. MP has verified this and I believe he has seen and measured most of the high end pjs. On the current new displays, it was only a matter of time before they started perverting the numbers. Once some marketing guy figured out that on/off was important, then well you know. The problem is how are you going to bust them on it. It is like an auto manufacturer saying they get 75 mpg without saying they did it going downhill with the clutch depressed at 30 mph. I think flat panel LCDs are maxed out around 2k to 1. Plasmas are better and digital pjs can vary from low to high. After seeing a demo by TI, I guessed that 20k to 1 would satisfy most CRT fanatics. Even though Darin said the demo wasn't that high, I stand by that statement. I know Draganm and some others who have seen the JVCs with between 15k - 30k to 1 have been impressed.

I was just thinking of this before this topic came up. I wonder what it would take to duplicate the various on/off crs on a CRT monitor. It would give an indication of what threshold one might be able to live with.

[WanMan]