CurtPalme.com Home Theater Forum

freidich · Posted: Tue Jan 15, 2013 8:53 am Post subject: soft image at 1080p

What causes the image to be soft at 1080p? Is there anyway to reduce this softness, i.e. a video processor, bigger screen, better porch settings, etc?

Also, since 1080p is soft, does that make a 4K 2.4:1 blend (2x 1920*1600) entirely impractical?

Projector is NEC XG1351LC

thanks again yall

km987654 · Posted: Tue Jan 15, 2013 9:31 am Post subject:

While I am sure there are more technical explanations the softness is the lack of video bandwidth required to display 1080p. There are a number of blend owners that could chime in on the blend aspect.

What projector are you talking about?

barclay66 · Posted: Tue Jan 15, 2013 9:39 am Post subject:

Hi,

In essence there may be three factors contributing to this effect:

- Not enough video bandwith -> Shouldn't be the case with the XG1351LC as it's specs describe that it has enough (150 MHz). As I don't have such a model I can't determine if it's really able to deliver accordingly. You might need additional information from other XG owners.
- Spot size too large -> Could be the case if electronic focus, astig and convergence haven't been dialed in perfectly for this type of input signal (e.g. settings were made at 720p, 1080i etc.). The smaller tubeface (8") and aged tubes would surely be counterproductive although it would somewhat soften the picture at other resolutions too (maybe not that noticeable).
- Video chain issues -> Could be the case if scaler, video processor etc. have a low bandwith limit or if video processing devices "eat" picture detail.

How to verify the possible issues:

- Directly connect a computer (using a high quality VGA->RGBHV cable) to the pj and set the resolution to 1920 x 1080 pixels at 60 Hz. If the picture is still soft, the spot size issue is probable -> Redo the mentioned settings at 1080p.

- If the picture is OK then check the devices at the video chain and find the weakest link -> Replace the culprit.

Regards,
barclay66

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

It depends on how soft is the picture... Even the best 8" machines can't do 1080P properly, but can get close enough to be very enjoyable.
There are several things that can cause softness on a CRT, generally: Lens system, electron beam focus, electrical bandwidth.
Probably the best thing you can do with a 8" machine is to use them at 1080i (@96Hz for example) to save bandwidth, however NEC XG's bandwidth is belongs to the very top group.
I have a NEC 6PG xtra and am using at 1080i-96Hz lately, driven from HTPC, and I must say it is very good from that machine, I can clearly read the small texts in windows, and with 1080P it's not much worse. So I guess these should be even better on an XG, but 1920x1600 would be insane for any CRT out there, 4K is not for CRT (or you need at least 4 of them)

kabuby77 · Joined: 28 Mar 2011 Posts: 147 Location: Italy

Nashou66 · Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY

If your watching 2.4 aspect movies mostly I would run 1920x800p@60. you'll need a HTPC or a VP to do this.

http://www.avsforum.com/t/737385/want-to-optimize-your-scaler-and-crt-calculations

Athanasios

**kal** · Posted: Tue Jan 15, 2013 2:54 pm Post subject:

What others have said is correct. What it basically boils down is one thing: Physics.

The electronics in the projector paints a picture on the tubes using an electron beam. The faster you try to paint (ie: the higher the resolution), the less time it has to do things accurately.

Think of the electron beam like a runner trying to turn sharp corners. The faster the runner is running, the more rounded their turns will be. To turn 90 degree angles the running has to to be almost walking. They cannot turn 90 degrees if they're sprinting.

High resolution means you're painting more on the screen at once in the same amount of time, so the beam has to move faster. Ie: The runner is running faster.

To be able to turn "tight corners" the electronics have to have extremely fast reaction times. That costs a lot of money in the analog world.

Kal

freidich · Posted: Tue Jan 15, 2013 6:18 pm Post subject:

Thanks everyone!

All your great answers have opened up more questions!

Note: All of my 1080p content is 24fps, so I will primarily be dealing with multiples of 24, although I will add 1080i and 720p @ 60Hz and 90Hz, respectively, for broadcast HD. I am using an HTPC for all content (and always will be).

Is there a formula for calculating necessary bandwidth?

If 1080i @ 96Hz works well, would 1080p @ 48Hz work also? Would it cause a significant enough "flicker" to make it not worthwhile?

ecrabb · Posted: Tue Jan 15, 2013 6:22 pm Post subject:

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

I prefer this site to calculate bandwidth and scanrate:
http://myhometheater.homestead.com/bandwidthcalculator.html
Yes, 1080P 48Hz has exactly the same bandwidth and scanrate as 1080i 96Hz, but 1080i will flicker less at the cost of the scanlines may become visible, it will totally depend on you, but from projector view they are exactly the same.

ecrabb · Posted: Tue Jan 15, 2013 6:35 pm Post subject:

freidich · Posted: Tue Jan 15, 2013 6:54 pm Post subject:

Awesome, thanks!

MikeEby · Joined: 24 Jun 2007 Posts: 5237 Location: Osceola, Indiana

Spanky Ham · Joined: 22 Mar 2006 Posts: 5643 Location: Comedy Central