How does scaling work in CRTs? - AVS Forum
Forum Jump: 
 
Thread Tools
post #1 of 7 Old 11-07-2013, 06:50 AM - Thread Starter
Member
 
pqwk50's Avatar
 
Join Date: Oct 2013
Posts: 74
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 23

My CRT says it can display 480i, 480p, 720p, and 1080i. But does it effectively have a "native resolution" like LCD & Plasma TVs do requiring some sort of scaling when dealing with different image resolutions?

 

For example, if the CRT is fed a 480i image, does it have to scale it in any way? An LCD TV would have to scale a 480i source to 480p (at a minimum).

pqwk50 is offline  
Sponsored Links
Advertisement
 
post #2 of 7 Old 11-07-2013, 07:58 AM
AVS Special Member
 
Floydage's Avatar
 
Join Date: May 2009
Location: Fort Worth, TX
Posts: 1,438
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 8 Post(s)
Liked: 35
Nope:

http://www.ehow.com/facts_5608283_native-resolution-hd-crt-tvs_.html

http://en.wikipedia.org/wiki/Native_resolution

Note that a 1080p LCD has to be scaled to 1080p.

Floydage is offline  
post #3 of 7 Old 11-09-2013, 02:01 AM
Member
 
hoffo's Avatar
 
Join Date: Jan 2008
Posts: 147
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 12
While CRTs don't have native resolutions, when speaking of HD CRT tvs they are usually made with 1080i in mind. Most will only display 480p / 540p and 1080i. 720p is either scaled to 1080i or 540p and not displayed as actual 720p. When speaking of CRT computer monitors or high end presentation monitors these are usually capable of 720p and sometimes even 1080p or beyond. Dot pitch of the display is what is important especially for CRT computer monitors. For example I have a 17" Sony CRT PC monitor that is 16" viewable with .24 dot pitch and according to the manual the recommended resolution is 1024x768. I run it at 1152x864 @85 Hz and it can do up to 1600x1200 @ 60 Hz but text legibility and sharpness seem to be best around the recommended resolution.
hoffo is offline  
post #4 of 7 Old 11-10-2013, 12:28 AM
Senior Member
 
LiquidSnake's Avatar
 
Join Date: Apr 2007
Location: Miami, Florida
Posts: 304
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Liked: 15
A CRT doesn't scale its output. The spread of the electron beam is adjusted and this gives you the resultant resolutions. The only reason a television CRT uses just a few resolutions (480i/p 1080i) is because the circuits driving them weren't made to do other resolutions due to a general lack of need. They are still not strictly scaling in the manner you are thinking of.
LiquidSnake is offline  
post #5 of 7 Old 11-10-2013, 08:12 AM
AVS Special Member
 
Floydage's Avatar
 
Join Date: May 2009
Location: Fort Worth, TX
Posts: 1,438
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 8 Post(s)
Liked: 35
I'd read somewhere that 1080p required too much expensive circuitry for a CRT TV, something to do with much higher power supply requirements and proportional to screen size (hence TVs vs. monitors). I think maybe the same for the most part with 720p as the requirement increases with progressive scan at higher resolutions. So I'm wondering if this handful of HD CRTs that can do 720p have beefier circuitry or are just converting the signal before scanning?

Floydage is offline  
post #6 of 7 Old 11-10-2013, 05:32 PM
AVS Special Member
 
blue_z's Avatar
 
Join Date: Feb 2006
Location: So Cal
Posts: 1,026
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 18
Quote:
Originally Posted by Floydage View Post

I'd read somewhere that 1080p required too much expensive circuitry for a CRT TV, something to do with much higher power supply requirements and proportional to screen size (hence TVs vs. monitors)
I'd agree with the first half ("expensive circuitry") more than the latter half ("power supply requirements"). Low-persistence phosphors and high-bandwidth electronics seem to escalate in price a lot faster than power supply capacity.

"TVs vs. monitors" is an ambiguous comparison. Video monitor? Broadcast monitor? Computer monitor? The silly "TV/monitor" marketing term applied to consumer-grade TVs with video inputs?
Quote:
Originally Posted by Floydage View Post

I think maybe the same for the most part with 720p as the requirement increases with progressive scan at higher resolutions. So I'm wondering if this handful of HD CRTs that can do 720p have beefier circuitry or are just converting the signal before scanning?

720p has a refresh rate of 45KHz, whereas 1080i is 33KHz and 480p is 30KHz.
Or in other words, 1080i requires only a 10% increase in refresh rate over 480p, but 720p requires a 50% increase.
So the answer depends on the cost of higher bandwidth versus costs of a deinterlacer+scaler. Or, in the days before ATSC tuners, simply reject 720p input.
I've seen one early CRT HDTV that would accept a 1080i video signal, but not a 720p. The electronics and tubes (it was a rear projector) didn't have the bandwidth to do 720p, and a deinterlacer+scaler wasn't inexpensive enough at the time. (It didn't have an ATSC tuner to nix that question.)

I have a flaky CRT projector that can display 1080i without a problem, but has issues with (the higher refresh rates of) 720p as the unit warms up. Seems like as the PJ heats up to normal operational temperature, the bandwidth capability of the circuitry decreases. The cause is not likely to be a power supply issue because the PSU has a cooling fan, whereas the CRT electronics rely solely on natural convection for cooling.

Regards
blue_z is offline  
post #7 of 7 Old 11-11-2013, 08:01 AM
AVS Special Member
 
Floydage's Avatar
 
Join Date: May 2009
Location: Fort Worth, TX
Posts: 1,438
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 8 Post(s)
Liked: 35
Good points and related. They claimed the higher speed required of a CRT required much more charge in the high voltage power supply (and the requirement went up rapidly, like you show with the refresh rate). So based on this it would not only have more expense due to higher bandwidth circuitry but for the more expensive section of the TV's power supply as well. Think about it - CRT HDTVs were competing with plasmas so why wouldn't they also be capable of 720p (or higher? was plasma capable of 1080p back then?). And then when ATSC tuners were integrated there had to be a conversion for the 720p stations.

Sorry, I got lazy and should have wrote computer monitor. Yeah I'd like to forget about that silly TV/monitor marketing term. smile.gif

Floydage is offline  
Reply Direct View (single tube) CRT Displays

User Tag List

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page


Forum Jump: 

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off