CurtPalme.com Home Theater Forum

opv · Joined: 18 May 2010 Posts: 202 Location: Emek Hefer,Israel

Hi,
I'm trying to understand a basic principle.
what is the effect of the raster width on the projected picture quality, assuming that the picture width on the tube is identical.
in the attached files, I have two cases in which the projected image size is identical.
In the first case,A, the picture fills most of the raster.
In the second case,B, the picture is narrow (due to poor source timing), comparing to the raster.

If I understand correctly, in the two cases the used "CRT bandwidth" is identical because the two pictures use the same phosphor area.
However, the "electronics bandwidth" used in case A is larger and the picture in case A will be sharper than the picture in case B.
Is my explanation valid or am I missing something?
Thanks,
Or

Tim in Phoenix · Joined: 21 Oct 2006 Posts: 4409 Location: Phoenix

Hello

Example B will not happen as the scan rate in 1080I HDTV for example is 33khz, so there will be 30 microseconds per line, mostly pixels, with a short retrace time. Perhaps an engineer in the crowd can explain this better.

.

opv · Joined: 18 May 2010 Posts: 202 Location: Emek Hefer,Israel

Hi Tim,
Example B is happening in my HT. maybe my description isn't good enough.
I'm trying to figure out weather I should make the effort and switch to case A. not a simple task for me, requires a new source device.
The resolution is 1080P@50Hz.

gjaky · Joined: 05 Jun 2010 Posts: 2802 Location: Budapest, Hungary

Example B is the case where the front porch and back porches are too big, decreasing porches gives you better filling of the raster, but you must leave enough "space" for sync signals for troubleless operation. Unfortunately there is no ultimate timing for CRT projectors, every brand has it's own recipe for syncing.

opv · Joined: 18 May 2010 Posts: 202 Location: Emek Hefer,Israel

gjaky,
Thanks for your reply,
On my setup, the situation is closer to case B than it is to case A. I can see the the 1080P resolution lines using test patterns without any jail bars or edge distortion.
My question is what is the effect of "better filling of the raster" on the picture quality.
Will it make the picture sharper, cleaner, more stable?

CasetheCorvetteman · Joined: 09 Nov 2008 Posts: 6326 Location: Australia

Youll stand alot less chance of banding and the image could possibly be better.

opv · Joined: 18 May 2010 Posts: 202 Location: Emek Hefer,Israel

So, I understand you have no conclusive answer regarding the effect of raster filling on picture quality?
What about noise? does the PJ work harder in case B comparing to case A and thus generates more heat ?

gjaky · Joined: 05 Jun 2010 Posts: 2802 Location: Budapest, Hungary

Theoretically the raster filling HAS effect on bandwidth (hence picture quality), but there is no real issue since the standard timings are constructed to maintain balanced bandwidth requirements and reliability/compatibility. There is no point in using 2000 pixel long scanlines when the active pixel number is 1000, it would stress the source as well.

CasetheCorvetteman · Joined: 09 Nov 2008 Posts: 6326 Location: Australia

I know that on a PG, if you run the amplitude out to 100% it requires more geometry correction, so in theory the convergence board may run hotter... I dont know if others have a simular issue.

opv · Joined: 18 May 2010 Posts: 202 Location: Emek Hefer,Israel

well, it's not ideal.
the problem is that unless you're willing to spend big $$$ on a VP or use an HTPC as a source, you're stuck with the timing as it was configured on the source device, with no way to change the porches.
I'm currently using a video chain which includes a media player (PCH a110 like) connected through moome EXT2 to a BG1209s.
only one of the optional resolutions, set on the player, 1080P50Hz gives me a picture with no jail bars or raster ringing, but it also introduces this timing problem.
I simply want to understand how much improvement I will get by adding a VP or using an HTPC.

gjaky · Joined: 05 Jun 2010 Posts: 2802 Location: Budapest, Hungary

My 6PG xtra accepts all sources near perfectly, of course there is some difference in raster filling, but not folding over, no ringing on any resolution I've already fed to it. I use custom timings on my (HT)PC for maximizing active picture area in raster because NECs are picky for too wide rasters on tube (H deflection gets too hot)

opv · Joined: 18 May 2010 Posts: 202 Location: Emek Hefer,Israel

My BG1209s is quite picky on source configuration. My previous PJ, BG808s accepted almost anything.

CasetheCorvetteman · Joined: 09 Nov 2008 Posts: 6326 Location: Australia

Same with my XG Gjaky, although my 9PG Plain has a minor issue with a couple resolutions, 1920x1080i at 50Hz doesnt get enough width, and 1280x720p at 50Hz is way too narrow. Those are 2 of the 3 resolutions my H/K AVR put out, the other is 576p 50Hz. Ive noticed also that 1080i 50Hz seems to be a long way off center of the raster too, but that is on both XG & PG, and both can be shifted far enoufh that is not an issue.

Decibel · Joined: 31 May 2007 Posts: 904 Location: Roma - Italia

Read my topic

https://www.curtpalme.com/forum_archived/viewtopic.php@t=32184.html

I'm convinced that an owner of crt should always have a videoprocessor.

I want to make sure that the image is almost coincident with the raster.
To do this you need a videoprocessor that can manipulate the timing setting with custom values.

Or HTPC
... but if you have stand alone sources these can't operate correctly.

CasetheCorvetteman · Joined: 09 Nov 2008 Posts: 6326 Location: Australia

I use both source types.

opv · Joined: 18 May 2010 Posts: 202 Location: Emek Hefer,Israel

Decibel,
I've heard the slogan that a CRT PJ can only work with an HTPC or with a VP many times.
these options sure make the life of a CRT owner easier.
My question is more focused.
what is the effect of raster filling on picture quality?
Has anyone tried this experiment and played with porch values to see the effect on picture quality?