Ask HDBeat: err, we are stumped with this one
Whenever someone sends a question over to us, we research it in depth and then post our best answer. Some of these questions are tough, but we can usually come up with it though, but this is the first time we have been stumped -- we are hoping our readers can help us out on this one. SJ sent over this question that we just cannot come up with a solid answer for. I am planning to get an Xbox 360 soon, and an HDTV to go along with it. I decided to look for CRT HDTV's first since they provide the best picture and are cheaper, but I noticed that there are no CRT HDTV's with a native resolution of 720p (which is the 360's native resolution). All the CRTs have a res of 1080i...why is that? Is it some kind of industry standard or are there some technical issues related to it?
Does anyone know for sure (read: give sources) why there isn't any 720p CRT HDTVS?
Reader Comments (Page 1 of 1)
Dave @ Aug 17th 2006 1:52PM
Unlike LCDs or DLPs, CRTs are not fixed-pixel displays and thus do not have a "native" resolution. CNet's definition of native resolution explains more:
http://ecoustics-cnet.com.com/4520-3173_7-5084364-8.html
Despite being listed as "1080i" CRTs should be able to display a 720p signal with no problem. In this case 1080i most likely refers to the maximum resolution of the display.
bryan @ Aug 17th 2006 2:00PM
I am no expert, but mine upconverts all 720p to 1080i. I think it probably has more to do with the fact that CRT's can have 1080 lines of resolution at an affordable price point, and LCD, and DLP can not. 720p should have never been added to the HD standard. It just confuses people. I want the full 1080.
siva @ Aug 17th 2006 2:01PM
CRTs are analog and don't have a native resolution like LCDs and DLPs, etc. They don't have pixels per se and the electron gun can change the resolution. I think there are CRTs that can show 720p and 1080i. It is not converting but displaying as is.
Mike @ Aug 17th 2006 2:02PM
I think it goes something like this.
Cathode ray tubes are analog, with the electron guns, shadow mask, and phosphors and all that. They will display any resolution up to their limits imposed by the shadow mask, etc. (see, e.g., "multisync" monitors). There is not a fixed 1920x1080 or other sized pixel grid as there is with digital display panels.
Seems like it's the input circuitry that converts everything to 1080i because it closely matches what the display is capable of. Most CRT HDTVs seem to be able to display 1080 interlaced horizontal lines (not much different from 540p, and therefore not much different from 480 lines of SDTV), though they usually can't resolve anywhere near 1920 vertical lines. 720p would require a TV that could do close to at mythical 1440i.
Because CRTs are on their way "out" I doubt there will be much further development, even the Sony XBR2 that had something like twice the vertical resolution of prior CRTs is gone.
MikeS @ Aug 17th 2006 2:03PM
and why are the LCD and Plasmas 768p??????
Aren't CRT tv's really 540p/1080i? My hitachi rear projection set has settings for upconverting to 540p or 1080i.
Dan @ Aug 17th 2006 2:04PM
You have to remember that unlike flat panel displays, CRTs are inherently analog devices. There are no discrete pixels in a CRT tv so there is not nessecarily the concept of upscaling (and the associated problems) that you will find with a LCD or Plasma.
Some CRTs are fixed and will simply upsample all inputs to 1080i, yet others are much more flexible. The Sony Kd-34XBR970 for example will take 480i sources and simply double them to 960i rather than upconvert them to 1080i. It can display 720p just as easily.
A set like the 970 will give you the most flexibility when displaying sources of all resolutions.
Jared Rice @ Aug 17th 2006 2:08PM
I don't have a source (not that anyone else did), but I believe CRT's can't display progressive signals; they have to interlace the signal before they display it.
henning @ Aug 17th 2006 2:11PM
Yeah, I thought there was a Sony CRT that did both 720p and 1080i.
Ben Drawbaugh @ Aug 17th 2006 2:19PM
Jared,
Actually all Computer CRTs are progressive and many display 768p as well as 1440p.
The question is why are there no consumer 720p CRT TVs.
My CRT TV can display both 480p and 1080i natively. When my TV was calibrated it was charged per scan rate.
540p shares the same horizontal and vertical sync frequency as 1080i, that is why all 1080i TV's can display both. 1440i as others mentioned is also at the same refresh rate.
Bryan,
720p was included because some broadcasters preferred progressive scan and liked the fact that it required less throughput than 1080i.
DaveH @ Aug 17th 2006 2:25PM
As a side note, some CRT's don't input 720P - Panasonic, IIRC. My Sony 30XS955 is wonderful.
SJ @ Aug 17th 2006 2:25PM
Thanks guys I think I understand the issue now. CRT TV's should be able to display 480p, 720p and 1080i without any up/downconversion since they don't have a native resolution, but most TV's upconvert all sources to 1080i.
From the CNET link Dave gave:
"Other types of displays, such as CRTs, create pixels independently of the physical structure of their screens and do not have a native resolution. As a result, a CRT's image quality is generally the same across a range of resolutions. "
DaveH @ Aug 17th 2006 2:30PM
Oh, and I think there was a Sampo CRT that was 720P, but it is old and out of productions. Most CRT's do 1080i better, although since they aren't a fixed pixel device, that is a misnomer. I believe the SFP (super fine pitch) tube in the top of the line sony's can resolve around 1400 lines. Unfortunately, the last SFP tube being sold is the Sony 36XS955. Which is probably a good recomendation for our gamer (note, its a 4:3 tube, note 16:9, not that should matter). The XBR970 is not a SFP tube and isn't as nice. The XBR960 is, which would be good if he wants widescreen, and can find last years model somewhere.
cckrobinson @ Aug 17th 2006 2:33PM
The user subysouth over at the www.hidefforum.com had this explanation which seems reasonable to me:
"subysouth
03-02-2005, 10:46 AM
The reason why there are not many direct view TVs made that will handle 720p is cost. TV picture tube for years have been based on roughly 480 video scan lines top to bottom. Getting them up to 540 for the 1080i format (remember that's two scans of 540 each) was not much of a problem as compared to the 720 lines required for the 720p specification. Another issue is the scan mask in the picture tubes. The scan mask is a plate mounted behind the inside surface of the CRT that has holes in it to allow the electron beam only to get through to the phosphors where there is a dot to be displayed on the screen. If you refer to the link maximus gave (See URL below) for the 34" Monivision, you will notice that unit has a 0.36mm Super Fine Pitch. That means each pixel is 0.36mm in size, which is very good for a TV monitor. Many computer monitors up to 19" will have a 0.28mm dot pitch. Either way, this is expensive technology and would explain why they are not widely available.
Now take the 0.36mm pitch and multiply it by 1380 dots for the width of a HDTV picture operating in the 720p mode and you wind up with a picture width of 496.8mm and with that set being 580mm wide overall, it works out. Most direct view TVs will not even publish their dot pitch as most are in the .50mm or greater range.
"
The monitor referenced in the explanation is this one:
http://www.digitalconnection.com/products/directview/dm7352sf.asp
It claims to have a maximum resolution of 1920 x 1080i, but the recommended resolution is 1280x720p. It's technically more of a PC monitor than and HDTV, but that still counts doesn't it?
Rob Stevens @ Aug 17th 2006 3:15PM
I'm not sure how accuarate this information is any more, but I remember back when HDTV was very new, I had conversations about the diference between 1080i and 720p. Apparently, 720p was harder to do in a CRT TV because of the length of the electron guns required 1080i could be done with 7" guns, but 720p required 9" guns, or something to that effect. Could be that this limitation is long since past, but this is what I remember from "back in the day".
Jon @ Aug 17th 2006 3:42PM
Another reason you don't get 720p60 CRT TVs is the horizontal scanning rate. 480i SDTVs have a scanning rate of 15.734kHz and for 480p just double that (31.468kHz). Similarly 1080i30 has a scanning rate of 33.75kHz. However, 720p60 neeeds 44.9kHz. Supporting a higher scan rate needs stronger magnetic fields and hence higher cost.
Mike @ Aug 17th 2006 3:44PM
Rob in comment 14,
I think you might be thinking of front projection CRTs (remember those?). Back in the day, they could be had with 7", 8" and 9" RGB tubes. Obviously, the bigger the tubes, the brighter the projector and the higher the resolution. For all the reasons above (i.e. that 1080i is about as hard to do as 540p), you needed larger, higher resolution tubes to do 720p. CRT projectors with 9" tubes were and are ridiculously expensive.
I remember seeing HD, I'm guessing 1080i upscaled by some super fancy Runco or Faroudja scaler, at CES displayed by two stacked CRT projectors with 9" tubes each (I guess the box split the alternate scanlines between each projector, and alignment of the signal would probable be horrendously tedious). It was gorgeous, looked like film, without many of the problems of digital projectors (e.g. shitty black levels), but damn, that setup was like a quarter mil.
Carlos Muniz @ Aug 17th 2006 4:25PM
Here's my two cents...
I am planning to get an Xbox 360 soon, and an HDTV to go along with it.
Good Choice...
I decided to look for CRT HDTV's first since they provide the best picture and are cheaper,
A CRT HDTV will not provide the better picture but they are cheaper. On the sole basis of the digital to analog conversion you will lose quality and introduce some type of signal interference.
but I noticed that there are no CRT HDTV's with a native resolution of 720p (which is the 360's native resolution).
It would cost to much to make a small progressive CRT to place inside a projection television. They do have what they call "Display Monitors" for video production and editing but they're in the thousands.
All the CRTs have a res of 1080i...why is that? Is it some kind of industry standard or are there some technical issues related to it?
Progressive monitors cost to much.
zachary @ Aug 17th 2006 5:18PM
I purchased a Sony CRT HDTV to use with my Xbox 360, for the same reasons you want to. It looks great and works well, I recommend it.
GhostDoggy @ Aug 17th 2006 9:18PM
JOn (#15) is correct. It is all about the bandwidth available and the determined scanrate for common HDTV resolutions vs. the regular TV resolution. This is why 540-progressive has essentially the same bandwidth as 1080-interlaced.
In fact, I have an old RCA DTC-100 combination ATSC tuner and DirecTV box. It outputs 1080i for HD and deinterlaced and scales NTSC to 540P. Trying to get 720P requires more bandwidth (higher scanrate), and more electronics.
One should not be surprised that a TV can take 720P and convert it to 1080i instead of simply displaying it as 1080i. First, it is easier to scale & interlace 720P to 1080i than it is to display 720P natively.
Imagine the reverse (deinterlacing 1080i and scaling to 720P). Since you cannot scale an interlace signal, you have to frame by frame deinterlace 1080i (very processor intensive to do it right), which is not trivial, and then scale it down.
I love my CRT displays. From the three computer monitors, to the RPTV, to the two front-projection CRTs. My front projectors are multisync (like the computer monitors) which basically means they can accept a variety of input signals as long as they are within the H & V scanrates the projector is capable of.
Zach @ Aug 17th 2006 9:33PM
It should be noted the that the Xbox 360 does NOT have a native resolution. It depends upon the game being played, ie Call of Duty 2 is a game that is rendered at 720P by the Xbox 360 (and is scaled to 1080i if chosen by the user.) And the same vise versa.
Nick James @ Aug 18th 2006 3:54AM
My TV supports both 720p and 1080i. It's a Sony CRT from a few years ago. I believe their Wega XBR TVs still support.
For the record, it looks like pure pants. It just needs more component inputs and another HDMI/DVI input.
Surprisingly, it has HDCP. Lucky me.
...it also weighs more than my house.
vaa81 @ Aug 18th 2006 7:21AM
Actually, I work at wal-mart and we carry two CRT's at my walmart with a maximum resolution of 720p. A Sanyo 30" and a phillips 30". I cant remember the exact price, but it's $478 for the sanyo I think and around $500 for the phillips.