CurtPalme.com Home Theater Forum

[picree]

From reading and learning I seem to recall that gamma is one of those things you just get from the projector. You can't adjust a pot or a setting to change gamma (that's what I read and recall). Well, I'm playing with HCFR and I notice that the gamma plot does indeed change. I started at 2.22 and I've seen results up to 2.35. My objective is to simply set my gray scale. How am I changing the gamma?

I'm tweaking four controls. Three are standard adjustments and the fourth is not supposed to be touched but I touched it (I'll explain):

1) Of course I set Brightness (just so I can see 5% black bar) and Contrast (targeting about 12 FL).
2) Of course I have been adjusting the R&B bias and gain.
3) I then go back and check the G2's for each tube to make sure they are still fine. So far standard stuff.

4) But I've also put a scope on the RGB output amps (been advised I shouldn't have messed with them). As per the manual, with an input of Black=2.0V and White=4.35V I have set the output at Black=185V and White=85V. I did this because I was having a hard time with the blue bias (I couldn't go down low enough to get a perfect gray scale ie. I had too much blue).

Which of these controls (or combination) changes the gamma plot and how?

If the adjustment of the output amps is changing gamma then should we be talking about what would or should be the best output amp settings for home theater? I mean the standard is 2.22 but I've read that a light controlled theater would look better if it was 2.5.

Anyone?

Aside: I admit I'm having a heck of a time setting the RGB amps. They seem to be EXTREMELY touchy. Three nights and I have yet to get them set in such a way that my R&B bias and gain settings are comfortably within range (I can hit the target values in the manual but I don't think my scope is accurate enough to get it right on). When I go back to set R&B bias/gain I always run out of span at the bias end for blue (and sometimes red). I will start another thread for this but I don't expect any replies because nobody messes with the output amps and the standard response has always been, "Don't touch them!".

[kal]

Yep, I wouldn't mess with the output amps.

Post your Luminance curve and your gamma curve too. The 2.22 and 2.35 values are just averages. It's important to see what you're doing too. My feeling is that as long as you're not way off (neither of your numbers are) and you're not losing low level detail you should be fine. That's why I'd like to see the low end gamma values and the Luminance curve to see how fast you're coming out of black. If it's not fast enough, you need a gamma boost from something like an RTC2200, Box1020/1021, Moome card/box, scaler adjustments, etc.

Kal

[kal]

Yep, I wouldn't mess with the output amps.

Post your Luminance curve and your gamma curve too. The 2.22 and 2.35 values are just averages. It's important to see what you're doing too. My feeling is that as long as you're not way off (neither of your numbers are) and you're not losing low level detail you should be fine. That's why I'd like to see the low end gamma values and the Luminance curve to see how fast you're coming out of black. If it's not fast enough, you need a gamma boost from something like an RTC2200, Box1020/1021, Moome card/box, scaler adjustments, etc.

Kal

[picree]

Here is one of the Luminance and several gamma plots showing the variation. Ile is helping me in another thread as I try to get the RGB levels right, as seen in the luminance plot...(something might be related to a new green tube). But I'm curious as to how I'm "changing" gamma. They are in reverse order (and the coloring of the jpegs exported from HCFR is awful) but you can see if you go from gamma.jpg up to gamma3.jpg the average gamma of my projector keeps going up starting right at about 2.2 and up to about 2.45.

I thought what everyone called "gamma" was fixed for your projector and couldn't be changed.

BTW-I have a tse gamma box I built so coming out of black is usually pretty good.

[emdawgz1]

I'm sorry but i feel i must.....


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Effect: power to bring about a result : influence <the content itself of television…is therefore less important than its effect — Current Biography>

[kal]

Just cut and paste from HCFR - that's what I do. Much easier to read.

You don't seem to have a 10 IRE gamma point. I'm worried it's very high given the trend at the lower end.

Here's mine using ean RTC2200 box with about 11 turns:



I'm going to try 12 turns and see if it gets closer to the 2.2 target. The sold yellow line is after greyscale calibration and with gamma. The dotted yellow is before greyscale (Barco 6500K default) and no gamma.

Kal

[kal]

Just cut and paste from HCFR - that's what I do. Much easier to read.

You don't seem to have a 10 IRE gamma point. I'm worried it's very high given the trend at the lower end.

Here's mine using ean RTC2200 box with about 11 turns:



I'm going to try 12 turns and see if it gets closer to the 2.2 target. The sold yellow line is after greyscale calibration and with gamma. The dotted yellow is before greyscale (Barco 6500K default) and no gamma.

Kal

[picree]