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Discussion Starter · #1 ·
Hello all, i have a question that is for the sake of knowledge only, not for any porblems.


From what i understand, all digital tv "upconvert" the standard to NTSC signal of 480i to something in the neighbohood of 960i.


Now here is where i dont know if i understand this.....i assume that this is done because the design of the tv wont let it display the lower rez.


If this is the case how can they display a 480p signal from a progresive scan dvd player without upconvert??


My basic grasp of this situation may be totally wrong, if so i would like to know what is right!!!
 

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The difference is the interlace. Normal 480i which is the same as 525 lines if you include analog sync signals is really 262.5 lines each 1/60th of a second. These are called "fields" The next 262.5 lines are offset to fill in between the first 262.5 lines. So in interlace you don't really get 525 or 1080 lines all at once. Because our brains are slow processors we see all the lines except when fast motion exceeds the 1/60th second time slot. This causes motion jitter.


Progressive scan means all 525, 480 or 720 lines are scanned from top to bottom. This results in a more stable image such as on your computer screen. But at the expense of double he bandwidth becuase the signal now contains twice as much information at any given time. It is because if this that 1920x1080P is beyond current cost effective technology.


Becuase the CRT or whatever display technology must paint the picture with more lines in the same time space, the scan beam or in the case of LCD, pixel counter, must run twice as fast. This is why 480P has twice the horizontal frequency as 480i. 15.75khz versus 31.5khz for progressive.
 

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Let me make some assumptions. Instead of 960i you mean to say that 480i is doubled to become 480p. This is what a line doubler does.


Using 480p instead of 480i has a couple of reasons:


1)480p is easy to do with today's technology.


2)480p is more stable than 480i without adding information (which is what a line quadruplar does)


DVD players used to upconvert in the beginning because they only had interlaced decoder chips. DVD information is now mainly output straight to progressive from the digital realm.
 

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In the strictest technical sense, the lines are not doubled in 480i to 480p conversion as they are there to begin with. They just aren't available to view at the same time, time measured in sub seconds.


What the hardware in a "line doubler" of this type does is to store the first field in digital memory in let's say even addresses. the next field is stored in odd addresses. Then the entire memory is dumped to the display device as a progressive image. This image is shown twice to make a 60hz frame rate as 30 would flicker. You may have noticed a time delay takes place while these fields are being held in memory. Yes, that's an issue with lip sync. Higher end systems delay the audio to keep it in sync. Cheap built-in doublers may not bother since it's only 1/3th of a second delay.


When you go beyond this with "quadruplers" as you mentioned complex filtering and interpolation comes into play. Here you truly get what you pay for. High end consumer boxes can cost over $10K Broadcast grade units can cost over $100K.
 

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Discussion Starter · #5 ·
Thank you for your reply, but i dont know if my question was understood. I know the difference between 480i and 480p, but it is my undrestanding that all digital sets upconvert the signal. Sonys is called DRC and according to what they say it is 960i. I assume this is to get the picture to close of the native resolution of the set which is 1080i. Even though 960i is intelaced the image height is still 960 lines tall. How is it then that the display of a 480p, which would be only 480 lines tall can fill the screen vertically?? Do these units change the width of the scan lines?? If that is the case, why not display NTSC in its native format of 480i and reduce the on-screen artifacts that i have seen in so many digital tvs??
 

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You are correct that the Sony DRC advertises taking 480i to 960i, but I think that many others (Pioneer, I believe) take 480i to 480p.


Yes, I would assume the scan lines are either thicker or farther apart, but can't answer this for sure. The basic purpose of a line doubler is to adjust the resolution of a regular 480i image upward for a larger display, where the plain old 480i would look worse than on a smaller display. Yes, there probably is a chance of artifacts in any upconvert, but that depends on the quality of the doubler. The line doubler in the Pioneer Elites, for instance, are well known for producing an outstanding doubled display. Their technology apparently reduces various ugliness that would result from an image that was simply doubled.


I don't think that digital TVs necessarily make 480i look worse, but the larger screen size definitely does. A key difference in HDTVs that are out there is the quality of their line doubler -- if watching 480i content is important to you. That is why some sets look extremely flat when viewing 480i, and others produce a vibrant picture.
 

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I go back to the physics if interlace. Yes, a 960i is 960 lines tall, but not all have video at once. If you took a camera with a 1/60th shutter speed and synchronized the exposure to the end of vertical scan, you would see the following. A picture with 960 alternating lines of video and black. If you took the next picture of the opposite field or exactly 1/60th of a second later, then you would see the same thing except the video lines and black lines would be exchanged. In a progressive image all lines would have video no matter what time the picture was snapped.


Yes, the lines are basically thicker for 480P but really a 480P line equals two 960 lines. The 480P line simply occupies the space of the 960 video line and the 960 blank line and it does so eack 1/60th of a second.


The reason most consumer TV's double the lines is cost of manufacturing. To make a monitor that can scan at both 15khz and 31khz would require dual winding deflection yokes and much of the horizontal circuitry would need duplicate inductive components. These are the expensive parts. In today's technology it's actually cheaper to make a complex line doubler on a chip. Some say what about multiscan VGA monitors? How do they do it? Well ever see VGA monitor that can operate at 15khz? Not in the mainstream. Making a deflection system that can go from 25 to 85khz is doable. Going all thewas down to 15khz is much more difficult and expensive. It deals with octives or doubling of frequency, beyond the scope of this thread.
 

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interesting thread.. how does line doubling relate/compare to a dvd player's progressive output?


Is the dvd player doing the same sort of thing as a line doubler in that it's showing the same image every 1/60 second (doubling each frame, so to speak) or do they have increased bandwidth over a non-progressive dvd player and they actually send an entire 480p frame each 1/30 second?


does that make sense?
 

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"If this is the case how can they display a 480p signal from a progressive scan dvd player without upconvert?? "


Some one correct me if I am wrong about this......Line doublers do as others have said, Upconvert to 480p using the 240 line input. The extra lines are either replicas of the 240 set or interpolated lines. With a Progressive scan DVD Player you have full 480p resolution because the dvd can be read faster in the digital domain. I guess one may call it frame doubling. The extra lines actually carry unique information. Not just copies or interpolations..


Best of Luck, Max
 
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