Native Resolution Question

cmase45 · 08-21-2006, 11:01 AM

This issue has been bothering me for the last couple of days so I hope someone can shed some light on this issue that I'm having. I keep reading on different web sites that tv's will display all signals (1080i, 720, etc...) at their native resolution. While this makes sense, what doesn't make sense to me is that if this is true, then a tv with a native resolution of 720p (1280 x 720) receiving a 1080i signal, will down convert it to 720p? Or does that mean that the tv will accept the 1080i signal and display it at the tv's native resolution with not down coverting?
I also have a question about the output resolutions of the cable box. If the above is true (the tv displaying all signals to its native resolution), then it wouldn't matter what output resolution you set the cable box to given the fact that some broadcasting companies such as ABC and NBC broadcast either is 1080i or 720p. Is this statement true? I'm so confussed on this matter. If anyone can answer this debacle, I would appreciate it...thank you!

Jerry1808 · 08-21-2006, 03:04 PM

When you have a fixed pixel display (lcd,lcos,plasma etc.) the set will convert any incoming signal to its native resolution (in your example 720p). The only exception is if the input is the same res as the tv then no conversion is necessary.

I have two tvs, an lcos 1080p and a plasma 768p. On both sets no matter what supported signal is fed to them they will convert it to their respective native resolutions.

I also have a pair of Comcast dvrs that can ouput 480i, 480p, 720p and 1080i. No matter which ouput I choose the tv will convert it to native.

I've experimented betwen 720p and 1080i on both tvs and the display quality is virtually the same but I've decided 1080 has a slight edge so I use that on both tvs. Without getting all technical the electronics in both devices (tv and cable) just seem to have more synergy or work better together using 1080.

You can get buried in all the details but the bottom line is just use the device (dvd, cable box etc.) output that looks best to you.

**rbinck** · 08-21-2006, 07:45 PM

Jerry is correct in saying it is best to try the different outputs to see which works best. The reason is because there are different methods used in converting from one format to another. Another thing to try is to let the signal pass through the cable box unchanged.

See what is not known is how the TV or the cable box converts from format to format. Taking the 1080i source converted to 720p as an example, you used the term downconverting indicating the 1920x1080 pixel picture would be converted to a 1280x720 pixel picture, but that may not be what happens. The 720p (or 768p) display will be refreshed at 60 frames per second which matches up with a 720p broadcast signal, but the 1080i broadcast signal is two fields of 1920x540 pixels at 60 fields per second. Some sets convert by up converting the 540 lines to 720 and down converting the 1920 pixels per line to 1280. This maintains the temporal resolution of 60 refreshes per second and offers a temporal resolution improvement if the source is interlace video, such as a live sporting event at the cost of spatial resolution because you end up with a converted 1920x540 picture rather than a converted 1920x1080 picture.

As you thought the other method of converting is to assemble (de-interlace) the two 1920x540 pixel fields on to a single 1920x1080 frame at 30 frames per second and then refresh each completed frame twice. This causes some interlace artifacts since the two fields are captured 1/60th of a second apart, but that is the nature of interlaced video and only shows up on programs that were captured with interlaced video cameras. Movies would have both fields created from a common film frame and will not have the interlace artifact. Now days the interlaced video is almost only news and live events such as sports on channels that use 1080i.

There are some TVs that have very smart video processors that actually detect whether the video is interlaced or film based (progressive) and will actually switch between one mode and the other. They usually call one mode the video mode and the other the cinema mode.

Normally the cable boxes will not have a very smart video converter, so that is why it is best to try all combinations to see what look best for you as you won't necessarily know what device is doing what type of conversion.

cmase45 · 08-22-2006, 11:10 AM

So let me just make sure I understand everything. No matter what signal is coming out of the cable box, the tv will always display it at its native resolution. So if the signal is 1080i, the tv with a 720p native resolution will display the 1080i signal as 720p? If this is true, this now brings me to another arguement. Say you have a 1080p tv and the only signals available are 1080i and 720p. Does the tv upconvert the signal to 1080p? Or does the tv just display the signal as is? I apologize if I'm repeating myself, but I'm just trying to understand exactly what is going on with how the tv displays different signals and whether or not it has to convert the signal.

Bigloww · 08-22-2006, 11:21 AM

I,m no expert, but to my knowledge, in order for the display to be true 1080p the source has to be 1080p. Like hooking up a BR or PS3 player to it. Dish/cable or OTA does not and will not anytime soon to my knowledge, broadcast in 1080p. However the verdict is still out on the PQ difference between 1080i vs 1080p (if any at all)..

Here is a recent post that may clear up your questions.

1080i vs. 1080p clearly explained - finally!

BobY · 08-22-2006, 11:48 AM

The conversion of an interlaced signal to a progressive image is not an upconversion. Changing 480i to 480p results in a picture that is 720 x 480 resolution either way. Changing 1080i to 1080p results in a picture that 1920 x 1080 resolution either way. The only difference is in how it is presented for display.

An interlaced display will present the image as two alternating sets of lines (odd and even), which produces annoying flickering. A progressive display presents the image as one sequentiual set of lines for a smoother image.

If a display is progressive (typically fixed-pixel displays like LCD, Plasma, etc.), any interlaced signal will be converted to progressive for display, while progressive signals don't need to be converted.

There can be issues with the de-interlacing (conversion from interlaced to progressive) process as different manufacturers use different techniques for de-interlacing. Some methods reduce the vertical resolution and some methods reduce motion smoothness.

The conversion to native resolution is a separate issue which involves changing the resolution of the input signal to match the native resolution of the screen through a mathematical process called interpolation. This creates an estimation of what the signal would have looked like had it been captured at the native resolution of the display.

The best of all worlds would be to have a 1280 x 720 display for watching 720p signals and a 1920 x 1080 display for watching 1080i signals, as this avoids the conversion of resolutions, but the best compromise is a 1920 x 1080 display, as it will display 1080i/p at full resolution and not lose any resolution when displaying 720p signals.

One might think the best thing to do is feed a 720p display a 720p signal, but there are very few sources of true 720p signals (a few broadcast networks). Most material starts out as 1080i or 1080p and in those cases, any 720p version has been converted from 1080i/p somewhere along the line (at the network, at the broadcast station, at the DVD player or at the STB). In most cases (other than known 720p networks), I would input everything at 1080i and let the display do the conversion to native resolution as it is more likely to do a better job (but try the other inputs as well just to make sure).

It's not a cut-and-dry situation...

paulc · 08-22-2006, 04:28 PM

Actually, the only cut and dry thing is this weekend's series between my guys and the Red Sox.

Confused about "input everything at 1080i." Do you mean "set you STB to NOT do any scaling/resolution changing and let the TV do it?" Pretty sure if I set the STB for 1080i only, it does the conversion and then the (my) TV downscales to 1366 x 768.

BobY · 08-22-2006, 10:43 PM

If your STB has a "pass through" mode, I would use that. Most STB's don't do as good a conversion as most displays. Since the native resolution of your display is neither 1920 x 1080 nor 1280 x 720, you can't avoid the display conversion anyway. The fewer the conversions the better.

If the STB doesn't allow you to pass the signal through, then I would set it to 1080i as this would eliminate the STB conversion on the vast majority of OTA content. Except for a 720p network transmitting 720p content actually captured at 720p (not upconverted SD or downconverted 1080i/p), there aren't any sources of unscaled 720p (not even Hi-Def discs).

You will usually get better results downscaling 1920 x 1080 to 1366 x 768 rather than upscaling 1280 x 720 to 1366 x 768, as the downconversion will preserve some of the detail of the higher resolution signal, while upconversion can't add details that aren't there to start with.

paulc · 08-23-2006, 10:26 AM

"Pass through mode" suggests not so much a particular STB, but the software (this is a software function, not hardware). I understand a SA 8300HD under SARA has an actual "pass-through mode." A SA 8300HD under Passport/ECHO has no such mode. Passport folks need to set all possible "resolutions" in it's "Output Formats" setting, a backwards way, but results in the same thing, any scaling is done at the TV not the STB.

cmase45 · 08-23-2006, 11:07 AM

Thanks a lot everyone for all of your input. I'm starting to understand this issue a lot better now. One thing I want to get straight though is the issue of setting the output on the STB. From what everyone is saying, it seems that setting the STB to 1080i is the best way to go to avoid a lot of conversions b/c most broadcasting is done in 1080i. I assume that setting the STB at 1080i would eliminate the STB scale the signal in most cases and letting the tv scale the signal to fit its native resolution. I would also assume that if the STB is set at 1080i and it recieves a signal other than 1080i such as 720p, this would be a case in which the box would convert the signal and then the tv would then scale the signal to fit its native resolution.

08-21-2006, 11:01 AM	#1
cmase45 What is HD? Join Date: Aug 2006 Posts: 3	Native Resolution Question This issue has been bothering me for the last couple of days so I hope someone can shed some light on this issue that I'm having. I keep reading on different web sites that tv's will display all signals (1080i, 720, etc...) at their native resolution. While this makes sense, what doesn't make sense to me is that if this is true, then a tv with a native resolution of 720p (1280 x 720) receiving a 1080i signal, will down convert it to 720p? Or does that mean that the tv will accept the 1080i signal and display it at the tv's native resolution with not down coverting? I also have a question about the output resolutions of the cable box. If the above is true (the tv displaying all signals to its native resolution), then it wouldn't matter what output resolution you set the cable box to given the fact that some broadcasting companies such as ABC and NBC broadcast either is 1080i or 720p. Is this statement true? I'm so confussed on this matter. If anyone can answer this debacle, I would appreciate it...thank you!

08-21-2006, 07:45 PM	#3
rbinck Administrator Join Date: Apr 2004 Location: Katy, Texas Posts: 12,337	Jerry is correct in saying it is best to try the different outputs to see which works best. The reason is because there are different methods used in converting from one format to another. Another thing to try is to let the signal pass through the cable box unchanged. See what is not known is how the TV or the cable box converts from format to format. Taking the 1080i source converted to 720p as an example, you used the term downconverting indicating the 1920x1080 pixel picture would be converted to a 1280x720 pixel picture, but that may not be what happens. The 720p (or 768p) display will be refreshed at 60 frames per second which matches up with a 720p broadcast signal, but the 1080i broadcast signal is two fields of 1920x540 pixels at 60 fields per second. Some sets convert by up converting the 540 lines to 720 and down converting the 1920 pixels per line to 1280. This maintains the temporal resolution of 60 refreshes per second and offers a temporal resolution improvement if the source is interlace video, such as a live sporting event at the cost of spatial resolution because you end up with a converted 1920x540 picture rather than a converted 1920x1080 picture. As you thought the other method of converting is to assemble (de-interlace) the two 1920x540 pixel fields on to a single 1920x1080 frame at 30 frames per second and then refresh each completed frame twice. This causes some interlace artifacts since the two fields are captured 1/60th of a second apart, but that is the nature of interlaced video and only shows up on programs that were captured with interlaced video cameras. Movies would have both fields created from a common film frame and will not have the interlace artifact. Now days the interlaced video is almost only news and live events such as sports on channels that use 1080i. There are some TVs that have very smart video processors that actually detect whether the video is interlaced or film based (progressive) and will actually switch between one mode and the other. They usually call one mode the video mode and the other the cinema mode. Normally the cable boxes will not have a very smart video converter, so that is why it is best to try all combinations to see what look best for you as you won't necessarily know what device is doing what type of conversion. __________________ www.highdefinitionblog.com www.BlogOfHawaii.com

08-22-2006, 11:21 AM	#5
Bigloww Shitter was full. Join Date: Apr 2006 Location: In a van, down by the river. Posts: 5,135	I,m no expert, but to my knowledge, in order for the display to be true 1080p the source has to be 1080p. Like hooking up a BR or PS3 player to it. Dish/cable or OTA does not and will not anytime soon to my knowledge, broadcast in 1080p. However the verdict is still out on the PQ difference between 1080i vs 1080p (if any at all).. Here is a recent post that may clear up your questions. 1080i vs. 1080p clearly explained - finally! Last edited by Bigloww; 08-22-2006 at 11:47 AM.

08-22-2006, 10:43 PM	#8
BobY What's all this, then?... Join Date: Jan 2006 Posts: 6,197	If your STB has a "pass through" mode, I would use that. Most STB's don't do as good a conversion as most displays. Since the native resolution of your display is neither 1920 x 1080 nor 1280 x 720, you can't avoid the display conversion anyway. The fewer the conversions the better. If the STB doesn't allow you to pass the signal through, then I would set it to 1080i as this would eliminate the STB conversion on the vast majority of OTA content. Except for a 720p network transmitting 720p content actually captured at 720p (not upconverted SD or downconverted 1080i/p), there aren't any sources of unscaled 720p (not even Hi-Def discs). You will usually get better results downscaling 1920 x 1080 to 1366 x 768 rather than upscaling 1280 x 720 to 1366 x 768, as the downconversion will preserve some of the detail of the higher resolution signal, while upconversion can't add details that aren't there to start with. Last edited by BobY; 08-22-2006 at 10:48 PM.

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08-21-2006, 03:04 PM	#2
Jerry1808 Home Theater Fan Join Date: May 2006 Location: seattle Posts: 831	When you have a fixed pixel display (lcd,lcos,plasma etc.) the set will convert any incoming signal to its native resolution (in your example 720p). The only exception is if the input is the same res as the tv then no conversion is necessary. I have two tvs, an lcos 1080p and a plasma 768p. On both sets no matter what supported signal is fed to them they will convert it to their respective native resolutions. I also have a pair of Comcast dvrs that can ouput 480i, 480p, 720p and 1080i. No matter which ouput I choose the tv will convert it to native. I've experimented betwen 720p and 1080i on both tvs and the display quality is virtually the same but I've decided 1080 has a slight edge so I use that on both tvs. Without getting all technical the electronics in both devices (tv and cable) just seem to have more synergy or work better together using 1080. You can get buried in all the details but the bottom line is just use the device (dvd, cable box etc.) output that looks best to you.

08-22-2006, 11:10 AM	#4
cmase45 What is HD? Join Date: Aug 2006 Posts: 3	So let me just make sure I understand everything. No matter what signal is coming out of the cable box, the tv will always display it at its native resolution. So if the signal is 1080i, the tv with a 720p native resolution will display the 1080i signal as 720p? If this is true, this now brings me to another arguement. Say you have a 1080p tv and the only signals available are 1080i and 720p. Does the tv upconvert the signal to 1080p? Or does the tv just display the signal as is? I apologize if I'm repeating myself, but I'm just trying to understand exactly what is going on with how the tv displays different signals and whether or not it has to convert the signal.

08-22-2006, 11:48 AM	#6
BobY What's all this, then?... Join Date: Jan 2006 Posts: 6,197	The conversion of an interlaced signal to a progressive image is not an upconversion. Changing 480i to 480p results in a picture that is 720 x 480 resolution either way. Changing 1080i to 1080p results in a picture that 1920 x 1080 resolution either way. The only difference is in how it is presented for display. An interlaced display will present the image as two alternating sets of lines (odd and even), which produces annoying flickering. A progressive display presents the image as one sequentiual set of lines for a smoother image. If a display is progressive (typically fixed-pixel displays like LCD, Plasma, etc.), any interlaced signal will be converted to progressive for display, while progressive signals don't need to be converted. There can be issues with the de-interlacing (conversion from interlaced to progressive) process as different manufacturers use different techniques for de-interlacing. Some methods reduce the vertical resolution and some methods reduce motion smoothness. The conversion to native resolution is a separate issue which involves changing the resolution of the input signal to match the native resolution of the screen through a mathematical process called interpolation. This creates an estimation of what the signal would have looked like had it been captured at the native resolution of the display. The best of all worlds would be to have a 1280 x 720 display for watching 720p signals and a 1920 x 1080 display for watching 1080i signals, as this avoids the conversion of resolutions, but the best compromise is a 1920 x 1080 display, as it will display 1080i/p at full resolution and not lose any resolution when displaying 720p signals. One might think the best thing to do is feed a 720p display a 720p signal, but there are very few sources of true 720p signals (a few broadcast networks). Most material starts out as 1080i or 1080p and in those cases, any 720p version has been converted from 1080i/p somewhere along the line (at the network, at the broadcast station, at the DVD player or at the STB). In most cases (other than known 720p networks), I would input everything at 1080i and let the display do the conversion to native resolution as it is more likely to do a better job (but try the other inputs as well just to make sure). It's not a cut-and-dry situation...

08-22-2006, 04:28 PM	#7
paulc Very Grizzled Vet of 1 yr Join Date: May 2006 Location: New York City Posts: 1,764	Actually, the only cut and dry thing is this weekend's series between my guys and the Red Sox. Confused about "input everything at 1080i." Do you mean "set you STB to NOT do any scaling/resolution changing and let the TV do it?" Pretty sure if I set the STB for 1080i only, it does the conversion and then the (my) TV downscales to 1366 x 768.

08-23-2006, 10:26 AM	#9
paulc Very Grizzled Vet of 1 yr Join Date: May 2006 Location: New York City Posts: 1,764	"Pass through mode" suggests not so much a particular STB, but the software (this is a software function, not hardware). I understand a SA 8300HD under SARA has an actual "pass-through mode." A SA 8300HD under Passport/ECHO has no such mode. Passport folks need to set all possible "resolutions" in it's "Output Formats" setting, a backwards way, but results in the same thing, any scaling is done at the TV not the STB.

08-23-2006, 11:07 AM	#10
cmase45 What is HD? Join Date: Aug 2006 Posts: 3	Thanks a lot everyone for all of your input. I'm starting to understand this issue a lot better now. One thing I want to get straight though is the issue of setting the output on the STB. From what everyone is saying, it seems that setting the STB to 1080i is the best way to go to avoid a lot of conversions b/c most broadcasting is done in 1080i. I assume that setting the STB at 1080i would eliminate the STB scale the signal in most cases and letting the tv scale the signal to fit its native resolution. I would also assume that if the STB is set at 1080i and it recieves a signal other than 1080i such as 720p, this would be a case in which the box would convert the signal and then the tv would then scale the signal to fit its native resolution.