CurtPalme.com Home Theater Forum

[gjaky]

Since my screen is quite small I run my 6PG xtra on low contrast (at 55 of 100, where 75 is the default) With this setting I get same brightness-density with a full white screen as with say 30% white 70% black content, which seems right to me. But if I set the contrast to default (75) I get higher brightness-density image with the 30% white pattern than with the full white. All PG that I've seen did this exactly the same way, I also paid attention to the little switches on the HV board, and even in "high-brite" mode (which is eventually a HV current limiter) the full white pattern loosed it's brightness-density. I guess this is the point of peak brightness measuring method, so I assume this symptom isn't unique to NEC PGs, however I find it very strange that this phenomenon comes up with the default contrast settings. Do you care about achieving even brightness density at all? Isn't this causing dynamic compression with bright images?

[opv]

That's one of the drawbacks of CRT technology. or any active display technology (I think) like plasma for example.
In theory, I think you can compensate this issue.
Lets say you use a relatively small screen, so you can reach 16FTL ansi lumens and not peak lumens with CRT.
In 100IRE filed you'll measure 16FTL but in 100IRE window, you'll get a much higher reading, say 30FTL.
If you measure the relationship between the input brightness (of a specific frame) and the output lumens of the CRT, you can invert this function by applying some sort of dynamic contrast in the source domain. I think you can implement such a mechanism on an HTPC or a VP.
Just a thought.

[CasetheCorvetteman]

You can set the contrast anywhere you like, and without telling us the KELVIN settings for the white end of the scale it tells us very little about how hard the tubes are driven, if you wind all 3 right up youll be setting the contrast alot lower to get the same output.

On my XG with the 125" screen ive got the contrast at about 67-68, and the white end settings are around low 30s for blue and green, 14 for red. Dont know about the white intensity for full white and the white box, ive never taken a whole lot of notice.

On my 9PG, some **** thought it would be a good idea to adjust the G2 pots, but again contrast about 72 and white settings are in the 40s, 110" screen with no masking around it yet.

[opv]

CasetheCorvetteman,
I think you're missing the point of the thread.
the problem isn't tube wear, the problem is that with CRT, you get different brightness depending on how bright the total image is.
You get a different FTL reading with a 100IRE frame and with 100IRE window.

[gjaky]

[CasetheCorvetteman]

My statement was nothing to do with tube wear, its adding the missing numbers to the equasion. You can set the contrast at 40 and still get the same brightness if you wind the KELVIN settings up.

[opv]

Sorry my mistake.
what do you mean by KELVIN setting? are you talking about changing the projector's light output by changing the RGB gain?

[gjaky]

Yes, KELVIN is the name of the menu on NEC projectors where you can adjust G2 and white levels. Of course I'm interested in others' experience with different branded pjs, I gave my findings on NECs just as a guidline.

[gjaky]

[opv]

gjaky,
If the picture isn't bright enough, of course you can't compensate that from the source side.
But if the picture is too bright, you can lower the contrast from the source side.
That's why I offered to adjust the contrast on the PJ to give sufficient ansi lumen (not peak lumen) and compensate all the other frames which aren't full 100IRE frame, by lowering the contrast from the source side.
getting sufficient ansi lumen with CRT, is only possible with relatively small screens, of course.
If you could change the contrast in the projector dynamically, it would be ideal. but it's much more complicated.

[digitalayon]

would a screen from blackdiamond work?

[Phoenixed]

One of those icky gray ones?

[gjaky]

What to do with screens regarding brightness cut off?

[CasetheCorvetteman]

Gjaky, the KELVIN menu adjusts white balance and colour temperature, but as you know, pushing all 3 colours up or down is basically the same as adjusting the contrast.