1) If my CRT based HDTV claims it can display 2 scan rates: 480p and 1080i, it that claim truthful? IOW, is it reasonable to assume it is really acting as a true progressive display when fed a 480 line source, either p or i?
2) Since the manual for the TV makes no mention of "540p", what is it doing with the 540p output from my external scaler? Richard, I know you didn't have time to fully explain it while you were here, but I need to understand the techincal reasons behind it. Is it acting as a progressive display or an interlaced display at that point?
As a note to anybody who has not seen the comparison, the Lumagen can output pretty much any resolution/scan rate you can imagine, but when 480i from the DVD player is scaled to 540p, it just plain looks better than 480i scaled to 1080i. I don't know why, but it does.
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1080I is 540 vertical lines 60 times a second. 540P is 540 vertical lines 60 times a second. Your TV does not know the difference and will report a 540P signal as 1080I. The difference is 1080I is 60 fields a second and 540P is 60 frames a second.
The reason 540P looks better is because you have removed interlace artifacts.
While it would appear on the surface that 1080I must be better than 540P since it has double the vertical resolution it doesn't mean a thing when you are scaling a lower resolution source.
1080I only means something if the original source was 1080I. To remove the interlace artifacts from that you would simply scale it to 1080P just like we do with 480I to 480P.
Note: The old Nintendos actually put out 240P which you used with your old 480I analog TV. It did not know the difference either.
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They both send 540 lines at a time.
1080i sends 2 groups or fields for each 1080 frame.
It sends the odd (or even) lines in the first field and the even (or odd) lines in the second field (interlaced). So it takes two passes to make a single frame.
540p sends a single group of 540 lines for each frame so the entire frame can be displayed in one pass (progressive).
Progressive is like this (lines): 1,2,3,4,5,6,7,8
Interlaced is like this (lines) : 1,3,5,7,2,4,6,8
Now another question for Richard: how does my Mitsubishi 55" diamond handle 480i/p versus 1080i? You said before it has 2 TVs - what exactly does that mean? I assume there are only one set of CRTs so is it just different programming? Is 480p scaled to 540p? What about 480i?
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The technical difference between 540p and 1080i is that with 1080i the STB puts every other vertical sync pulse in the middle of a line. With 540p all vertical sync pulses come between lines. A sync pulse in the middle of a line causes a half-line vertical shift in the next field, which is what interlacing is. If mid-line syncs are not eliminated then it is not really 540p.
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>>Progressive is like this (lines): 1,2,3,4,5,6,7,8
>>Interlaced is like this (lines) : 1,3,5,7,2,4,6,8
Progressive is like this (lines): 1,2,3,4,5,6,7,8
Interlaced, field 1 (lines) : 1,3,5,7, etc.
Interlaced, field 2 (lines) : 2,4,6,8, etc.
Ken, this is done by simply offsetting the first line back and forth and can be seen on a scope with delayed sweep. It has nothing to do with the vertical sync pulse and everthing to do with the horizontal sync pulse and the next line of information.
Your TV has two scan rates, two different circuits to do both scan rates and two different alignments for each scan rate. That means you will have artifact free imaging using 16:9 aspect with 480P or 1080I/540P scan rate outputs. This is something only a CRT can do. Digital displays have only one native scan rate and that is the pixel count.
540P does not exist in the world of capturing and mastering video content. It exists only as a scaling scan rate due to 1080I displays.
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480P does not require scaling and anything less than 480P is scaled to 480P. Your TV will not scale anything to 540P but you may have the Mits feature that converts any NTSC signal from 480P to 960I, not recommended.
What is 960I? A 30 frame version of 60 frame 480P.
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Richard: On page 7 of http://www.s3graphics.com/TN107A.pdf you can see a timing diagram from SMPTE 274 1998. It shows that the odd-field vertical sync pulse comes in the middle of line 563, while the even-field Vsync comes at the end of line1125. If the CRT monitor designer uses the Vsync to trigger retrace directly then no circuitry is necessary to get the monitor to interleave. I assume most CRT monitors are built this way. I don’t think the SMPTE has a spec for 540p, so whether 540p has 562 lines or 563 lines is something I couldn’t say. If the STB wants to put out 540p but doesn’t eliminate the mid-line vertical sync then you will see interlace artifacts in your 540p.
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When fed a 540p signal, is the 1080i display really a progressive display? Can I assume it is painting each one of the 540 lines with no spaces in between them, 60 times a second?
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If the 540p has no mid-line syncs then a strait-forwardly designed CRT will not interlace and will show true 540p. What a digital display will do, I don’t know. Personally, I have always doubted that true 540p exists. If your STB manual says nothing about 540p then it probably doesn’t do 540p. If your STB does true 540p then you might be able to see black between the scan lines, as with 480i or p. However some CRT monitors might sense 480 or 540p and switch to an oval scanning spot to hide the lines.
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Ken, this is actually from a Lumagen scaler, not a STB, using either DVD or analog cable TV for a source. It is doing a true 540p. The difference between 480i scaled to 540p vs 1080i was obvious - equal in magnitude to the difference between 480i and 480p.
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>>It shows that the odd-field vertical sync pulse comes in the middle of line 563, while the even-field Vsync comes at the end of line1125.
I would prefer not spending time on semantics. Do we both agree that 1080I and 540P is determined by the signal and not the display just like video gaming consoles?
>>If the STB wants to put out 540p
This thread is not about STBs and all about feeding a display a specific scan rate to perform a specific job. I have suggested on other threads in the past that the above scenario may exist for 720P conversion to a working 1080I scan rate for 1080I displays and may very well be 540P. Please start another if this is your point. Just a quicky; I have no documentation on this conversion to either scan rate so it will be a short thread.
>>What a digital display will do, I don’t know
All digital displays require scaling an interlace signal to a progressive format. That is the nature of how they work. Interlace is a cheap form of compression centered around mass market CRT based television design going back to the invention of television.
>>Personally, I have always doubted that true 540p exists
As a native format for video content you are entirely correct. That does not negate the fact that is does exist for the purposes of scaling.
>>When fed a 540p signal, is the 1080i display really a progressive display?
Absolutely. That is determined by the timing in the signal, not the display.
>>Can I assume it is painting each one of the 540 lines with no spaces in between them, 60 times a second?
Not exactly. With interlace the line spaces and tearing of edges only appear during scenes with motion. On a still image you should not have this effect but may very well note vertical line twitter, a by product of interlace.
With interlace you display one 540 line field at one position and the next 540 line field at a slightly different position, based on the incoming signal timing, which if the display is capable of such precision they will interleave perfectly. With progressive you display one 540 line frame at the same position all the time.
If you recall there was a thread posted about how 1080I should really be called 540I and deserved merit. This is based on the fact that 50% of the time you are perceiving only 540 lines and not 1080. This perception is based on the amount of motion in an image versus a still image. Why 1080I made it as an HD scan rate is a complex discussion. While it may have it’s faults with current product the future is very bright. I would suggest the most important point is this format can easily be converted to the HD scan rate of 1080P 30 frames by the broadcaster. Obviously that is easily 5-10 years down the road since the inception requires new broadcast equipment, DTV STBs and 1080P displays. In the meantime, as 1080P displays come to market, the end user can scale any HD 1080I source to 1080P and remove all interlace artifacts just like we do with 480I.
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