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OzMillsy
Joined: 10 Dec 2007
Posts: 25
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| Posted: Thu Jan 17, 2008 2:15 am Post subject: |
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| ecrabb wrote: |
I sit at about 10-11 feet from my 8-foot wide screen and I LOVE 1080i. Of course, my projector is soft enough that I can barely detect scan lines standing right at the screen. Conversely, it's sharp enough that I can easily read Windows desktop icon text at 1080i.
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I have to agree with you. 1080i should be right in the pocket (sweet spot) of most 7" systems.
I reckon the market is obsessed with 1080p , and dont realise that 1080i can be just as detailed and just as rewarding to watch.
There is a general belief that there is only half the resolution with interlacing. Which is not true at all, we are still talking about 1080 different lines of detail, being drawn in a way that is faster than the eyes can discern. And if you can discern line structure at 60Hz, up the RR to something higher with a scalar (or htpc).
A 7" CRT has got to be the cheapest route into HiDef available  .
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Person99
Joined: 09 Mar 2006
Posts: 4899
Location: Flower Mound, TX
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| Posted: Thu Jan 17, 2008 2:52 pm Post subject: |
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| mike calcott wrote: | I agree totally with Person99, You cannot get a device to output one resolution which magically ends up at another. It mathematically does not happen, but the arguement regarding interlaced vs progressive is interesting. If we go back to basics, when we used a interlaced source as nothing else was available, the big advance in picture quality was when DVD players arrived with progressive scan via component input. The principles still apply. Yes an interlaced signal with give an apparently more edgy picture because they are providing a coarser image at any one time, eg 1080i is only presenting 540 lines at any one time and the two interlaced fields make 1080. The progresive signal presents all of the field in one pass, as Person99 quotes it would take two fields of 650 lines two achieve 1300i. Most people think that the progressive image is softer than the interlaced image, this is mainly caused by overscaling to a degree that the scan lines overlap causing a softening of the image. A projector with 7" tubes normally has a sweet spot between 600-700 lines which ever way you wish to use them, and dialing up a higher resolution will result in a degraded image or in extreme cases can damage your projector.
The scaler I use can be calibrated in two line increments vertically and horizontally, and the refresh rates can be adjusted in 0.1hz increments in progressive or interlaced formats, I also can adjust luma, chroma, and gamma, and front and back porch adjustment.
I am happy with my scan line free image, but others like the interlaced image, each to their own preference. |
And I in turn agree here.
I would only add that there is also a bandwidth consideration. A CRT will get softer both as scan lines overlap and bandwidth increases. "On paper" progressive is ALWAYS better (especially for progressive sources). But, in the real world, I think there are other factors which may make one like one option better.
1920x1080 interlaced requires less bandwidth than 1920x720 progressive. So, the picture will be a little sharper. Also, movies are made up of a large number of relatively static images, thus between phosphor persistance and persistence of vision, you eyes merge them into 1 full 1080 field. I've compared 720p with 1080i extensively and there is more detail in 1080i from a 1080p source because there is more picture information. Is it without flaws? Of course not interlacing introduces three major artifacts:
1) Motion dependent resolution
2) Stair stepping on diagonal lines
3) Scan line visibility on white objects on most PJs.
Number 1 does not really occur if the source is progressive, so not a big problem for film and on the rare video content I watch that is truly 1080i sourced, I've not really been able to tell the difference between objects in motion at 1080i (which effectively means 540) and 720p. Your eyes just can resolve detail in objects in motion that well.
Number 2 occurs about 1-2% of the time at most.
Number 3 occurs about 5% of the time.
So, since I watch almost exclusively progressively sourced 1080p images, I prefer full resolution 100% of the time with artifacts 5-7% of the time. Some prefer less resolution 100% of the time and artifacts 0% of the time. There is no right nor wrong answer, just personal preference.
Although I'm see as the 1080i advocate, because I think it can be implemented well and look good and thus I encourage people to try it, I realize it does not work well for everyone in every situation. My PJ can kick out a decent 1080p. But it can look awesome around 850-900 lines. If I sat at 1.2x screen width, I would downscale to somewhere in that range because at that distance, I'd have scan line visibility 100% of the time and that is too much of an artifact for me.
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Dave
A train station is where the train stops. A bus station is where the bus stops. On my desk, I have a work station....
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Cine 7
Joined: 06 Jan 2008
Posts: 26
Location: Singapore
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| Posted: Thu Jan 17, 2008 3:40 pm Post subject: |
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| Quote: | | What you want is 1080i scaled to 1300i (which is two 650 fields). |
OK, I can see that I should have mentioned "1300i" in the beginning. I took it as a given that when I was talking about scaling 540 lines to 650 that the end result will be 1300i and not 1080i.
| Quote: | | 1080i -> 1080p -> 1300p -> 1300i |
That makes sense to me. Probably the better way of doing it.
| Quote: | | Also, constantly saying you wanted 1080i threw us too. We could have both saved a lot of time (and some of SC's) if you would have just said you wanted to scale a 1080i source to 1300i. |
My bad! 
| Quote: | | The reason I say "probably" is because no scaler will do what you want, and there is not nearly enough demand for it for them to add it (only CRT PJs can handle 1300i). |
Honestly, I didn't think there is really a scaler that would do this. The only interlaced output resolution I keep seeing in today’s scaler specification is 1080i.
| Quote: | | So, I would talk to the HTPC guys to see if Powerstrip and XYZ video card will let you do 1300i. |
Don't know if I want to venture into HTPC territory. 
| Quote: | | Not to sound like an a$$, but you can't buy a Kia and assume you can get Porsche performance! |
True, true.... but these days this is not as significant anymore that 10 or so years ago.... at least in electronics, is it? More is possible for less!
| Quote: | Correct, but if scan lines bother you that much, you probably have 4 options:
1) Downscale (as I suggested)
2) Sit further away or get a smaller screen.
3) Upgrade to a CRT PJ that can do 1080p
4) Upgrade to a digital PJ that can do 1080p |
Probably 4) 
| Code: | | Yes mate, but my point is, I would play with the refresh rate rather than the resolution, in order to get rid of the line structure you see. |
I haven really fiddled with refresh rates that much. Might be worth exploring. The Cine 7 has a bandwidth of only 75MHz though so not that much headroom.
Now, if someone could tell me how to calculate what kind of resolution/refresh rate adds up to 75MHz. How is the pixleclock calculated?
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Person99
Joined: 09 Mar 2006
Posts: 4899
Location: Flower Mound, TX
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| Posted: Thu Jan 17, 2008 4:03 pm Post subject: |
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Bandwidth is a funny thing. The more you have the sharper the picture gets. For 1080i/72 you need about 38 MHz bandwidth. If you have two times the bandwidth, the image gets very very very slightly sharper. If you have 3 times, it gets sharper still.
Extron published a paper saying devices between the source and display require 3x the bandwidth needed to not screw up the signal. Many people think that means you need 3 times the bandwidth in the display. That is not true.
Here is a bandwidth calculator, it uses the extron formula and a swag for retrace time, so to get the bandwidth you really need, divide its results by 3:
http://myhometheater.homestead.com/bandwidthcalculator.html
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Dave
A train station is where the train stops. A bus station is where the bus stops. On my desk, I have a work station....
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Cine 7
Joined: 06 Jan 2008
Posts: 26
Location: Singapore
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| Posted: Fri Jan 18, 2008 4:45 pm Post subject: |
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| Quote: | | For 1080i/72 you need about 38 MHz bandwidth. |
| Quote: | | Here is a bandwidth calculator, it uses the extron formula and a swag for retrace time, so to get the bandwidth you really need, divide its results by 3: |
I used the calculator to determine the bandwidth required for 1080i @72Hz. Parameters are as follows:
Horizontal Resolution: 1920
Vertical Resolution: 540
Vertical Refresh Rate: 72
The result is 112MHz.
Now, if I understand correctly I can device this by 3 which would give me 37.3MHz which is what is required form the display.
This is exactly half of 1920x540x72=74.6MHz?
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Person99
Joined: 09 Mar 2006
Posts: 4899
Location: Flower Mound, TX
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| Posted: Fri Jan 18, 2008 5:24 pm Post subject: |
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You have double the bandwidth you need to display 1080i/72.
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Dave
A train station is where the train stops. A bus station is where the bus stops. On my desk, I have a work station....
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Welwynnick
Joined: 04 May 2006
Posts: 229
Location: Welwyn, Herts, UK
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| Posted: Thu Feb 21, 2008 12:15 pm Post subject: |
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| Cine 7 wrote: | Now, if I understand correctly I can device this by 3 which would give me 37.3MHz which is what is required form the display.
This is exactly half of 1920x540x72=74.6MHz? |
| Quote: | | You have double the bandwidth you need to display 1080i/72. |
Is that because there are two pixels in a cycle?
This has been bugging me for ages. People often multiply the pixels by the frame rate and get the pixel rate, and assume that is the bandwidth. But bandwidth is in cycles per second, meaning a complete cycle through off-and-on. And that on-and-off takes two pixels (or lines or columns) to represent on the display, or putting it the other way you need one cycle for two pixels, and 960 cycles for 1920 pixels.
Taking blanking periods into account, you generally need 2200x1125x60 = 148.5 mpps for 1080p. That's beyond the bandwidth for even the best CRTs, but if you need one cycle for two pixels, the bandwidth requirement becomes 75 MHz. Does that explain why all those 9 inchers can still look still pretty good at 1080p, even if they have "only" 110 or 120 MHz? Since bandwidth is expressed at the -3dB point, it sounds like a bit of margin will help maintain fine detail, so I think we're good.
There's another issue with bandwidth that I never hear about, and that's whether BW refers to power BW or gain BW, but that's another matter.
regards, Nick
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