CurtPalme.com Home Theater Forum

[Nashou66]

Here is a post by Scott a while back called,

WTF is MTF?

MTF. Modulation transfer function.

It's a way to put a number on resolution. It looks good. I can barely see it. It is real sharp. Any of these statements can mean different things to different people.

Imagine a light meter that only looks a small slit a few thousands of an inch tall (or a tenth of a mm). If you put up an alternating line on line off pattern at 320 x 240 resolution you would see a bunch of horizontal lines. Now take your light meter and measure the light between the lines and the light at the peaks of the lines. You would measure something like what is shown in 100%.bmp drawing attachment. Because the light between displayed lines would be "0" (or something near zero) your MTF reading would be 100%.

Now increase your resolution to 1600 x 1200. The lines are much closer together now. In fact they are overlapping to the point where there is no longer "black" in between the lines. If the "black" you measure is now one half what you measure at the peaks your MTF is 33%. If you now go to 1536 lines you can imagine the "black" is even a higher light level and your MTF might only be 15%.

10-15% MTF is obvious. When you get down to 3-5% MTF it is getting hard to see with your eye.



Its not a square wave its more of how far apart the curves are or if they overlap.

100% MTF, this is defined black and white area.


33% MTF, lines slightly overlap and black area becomes more grey than black.


Also from the thread on how lens MTF is measured and the LP/mm

The better CRT lenses are rated at 10-12 line pairs per mm at a certain MTF. I'm guessing here but I think you get your line pairs from a piece of glass that has lines of metal deposited on it (ronchi rule). Twelve strips of metal seperated by equal width of clear glass in a mm. This is placed where the phosphor normally is and lit from behind by a lamp. This is projected on a screen and the MTF measured. Have never seen it done but would like to one day.

That was also from Scott, now I know your talking about the electronics and the Slew rate of op amps but i thought this was interesting as MTF was mentioned.

Athanasios

[ecrabb]

Athanasios... Thanks for posting that... Good refresher. I completely trust and understand Scott's characterization of MTF with respect to CRT...

But, I was speaking in more general terms... So, theoretically, a 1-on/1-off pattern can be represented by a square wave. In practice, optics, electronics, etc. prevent that from happening. The 33% graph above is very similar to what happens when you don't have enough amplifier power and drive it too hard - dynamic compression.

My main point, though - that horizontal resolution is limited primarily by electronics - is still valid.

SC

[Nashou66]

[ecrabb]

[VideoGrabber]

MikeEby wrote:
> I'll agree...with an XG is seems to have a bigger issue with horizontal resolution, vertical I could resolve fairly well. Here was a 1:1 screen shot @1080p@72Hz. Soft yes but the lines show some definition. <

Actually, this is very good performance at that rate. IIRC, you were using a Box 10x0 of some kind in the chain at the time?

It's good not only because the delineation between the vertical lines can still be discerned (horizontal rez), but because the amplitude of the signal has been maintained. I.e., the peak brightness is uniform. Almost always what will happen when a PJ is pushed this hard is that the vertical lines will be dimmer than the horizontal lines. And this is a factor frequently overlooked. When that happens, you lose contrast in the image... what's commonly referred to as "punch". That often degrades the perceived image quality faster than the loss in resolution, per se.

[VideoGrabber]

[macgyver655]

This is what you originally said:

"In the horizontal direction, resolution is most constrained by what Mike Parker calls the video chain's "speed" - basically, the video chain's slew rate - in essence, the frequency response. If the video amp's slew rate is too slow at a given frequency (resolution), the transition from black-to-white and back will be soft like a sine wave - resulting low MTF. If the amp's slew rate is fast enough at a given frequency, the transition from black-to-white and back will more closely resemble a square wave - resulting in a higher MTF. "

Then you came back and said: "

My main point, though - that horizontal resolution is limited primarily by electronics - is still valid.

Naturally electronics is what causes any limitation because thats all there is. Your first comment was aimed at just the video amps. Your second says electronics which would be more correct because there is much more involved and the amps alone would no accomplish much.

To state just the amps as a solution would be incorrect. It is much more complicated then that which is why I wanted to discuss this with Mike on the side as I'm sure he would confirm this. Even lens comments here are questionable.

[ecrabb]

I'd agree with you Mac, but I didn't state or even imply that that replacing amps would be any sort of solution to any problem. Here's my direct quote:

[CasetheCorvetteman]

All great reading and very informative thanks people Has helped me out alot.

[macgyver655]

[ecrabb]

Alright, fine. It implied "amp" even if I didn't intend it that way. Doesn't matter though, because you asked, and I clarified. No, I didn't mean Marquees... I don't know sh*t about Marquees... I was talking about projectors in general, as was the discussion with Mike I referred to earlier.

On lenses... How can you can say lenses can't be included in the issue of a projector getting softer at higher resolutions? I know what you're getting at, I think... The lenses don't make it "softer"... The lens' resolution is a fixed number... But, as you increase resolution and approach (or exceed) the resolving power of the lens, the image will indeed appear softer. The image might look perfectly (or more than acceptably) sharp at 600p in 4:3, but be very soft at 1080i 16:9. That effect was plainly obvious with my old 1271, and it was almost all the crappy HD-8's.

And why not discuss MTF? Isn't it the only way to objectively measure the true "sharpness" of a projection system? Not that any of us have the equipment to take the measurements, but how is it not helpful to at least understand the science of what's going on when the frequency response of the projection system falls below that of the desired output resolution?

Side note... Mac, I really enjoy reading some of your posts - and definitely enjoy learning from them. But, I'm REALLY starting to tire of the demeanor in your posts that if you read between the lines says, "I could it explain to you little people, but you're all so stupid, with your misinformation and ignorance, it's really not worth my time". Seriously, if you're not interested in the discussion and helping people out (as you do so often), then like you asked... Why bother posting at all? Just to make people feel stupid? In that case, perhaps you should just do like those other knowledgeable people...

Sorry, I just don't see the point in belittling people.

SC

[macgyver655]

[ecrabb]

No hards feelings here either, Mac... I'm sure it's just a bit of a personality conflict thing... You rub me the wrong way sometimes, I rub you the wrong way sometimes. No biggie - it happens. Some people just don't click like others. I think you and greg_mitch are the only two that I have any abrasive interactions with on any regular basis... And even most of that is pretty good natured. I certainly don't lose any sleep over it... Well, unless I'm writing a "you're full of sh*t and here's why post" to Greg at 2:30 in the morning.

If my requests for clarification or further info to you come off negatively, as if I'm implying you don't know what you're talking about, I apologize for that. But, I think I do that because so many of your posts seem intentionally vague, along the lines of, "I'm the expert so trust me when I say this, but you're dead wrong and obviously haven't a clue what you're talking about." Then no further explanation. That tends to annoy the sh*t out of me - especially in a forum like this with so many knowledgeable people with backgrounds and experience in a wide variety of fields.

I typically go overboard the other way when I write my posts, and completely over-explain myself... I suppose it's from being on the internet for years, and trying to anticipate the holes that will be shot through my post if I don't thoroughly explain myself. If I'm wrong, I fully expect somebody to point out how, why, and where and I'm wrong... But I'm not going to be friendly when somebody says I'm wrong and offers no further explanation beyond, "Because I'm the expert and I say so, that's why."

Cheers,
SC

[Spanky Ham]

[Mark_A_W]

Back to the topic....


Case

I played around with 1920x804p at 72hz on my XG.


And I could not tell any difference from 1920x1080i at 96hz.


So I just stuck with the single res, 1920x1080i at 96hz (called 48hz in powerstrip).


(And despite implied suggestions to the contrary, the only real difference between a top end 8"er and a 9"er is the tubes. There's no huge difference (as in orders of magnitude) in the performance of the electronics..well, until you get to a 909!).

[benareeno]

I still think an XGLC or G70 is superior to a 9500LC...

It seems to me that the biggest difference with going to 9 inchers is that they have an easier time lighting up a bigger screen. NEC focus is immeasurably better as demonts

[benareeno]

I still think an XGLC or G70 is superior to a 9500LC...

It seems to me that the biggest difference with going to 9 inchers is that they have an easier time lighting up a bigger screen.

NEC focus is immeasurably better as demonstrated when I was at ElainBenes's house and he had a worn XG on the floor and an 8500 on the roof...when we switched back and forth, the difference was not subtle...add in the color filtering and it's a no-brainer. The beauty of this test was that we could instantly switch back and forth within the same scene...

1080i at 48Hz...same bandwidth as 1080p 48Hz?? Do I need an ATI card to try that?

[benareeno]

perhaps I should say sharpness...not necessarily focus.

[macgyver655]

[macgyver655]