CurtPalme.com Home Theater Forum

benareeno · Joined: 22 Mar 2006 Posts: 1614 Location: ottawa, canada

I think Kal measured his gamma at 2.2...and that would likely be where most of our projectors would measure.

NOw...isnt's a dark theater supposed to look better with overall gamma 2.5?

If so..how do we get there? Aren't the gamma boosting boxes only doing a small manipulation of the low end?

Would a lumagen do it?

I would guess an HTPC would do it...along with low end boost, is that correct?

Any of you actually running a higher overall gamma?

David_Web · Joined: 02 May 2007 Posts: 418 Location: Sweden

2.5 is pretty much where a CRT lands. Only needs a little boost at the low end.
At least for my Marquee if my measurements where accurate.

2.2 for me needed more boost over most of the lower range.

I try to get around 2.4 as it gives a tiny bit more low end detail without ruining the punch too much.
It's all preference in the end.

stefuel · Posted: Fri Jul 23, 2010 4:22 pm Post subject:

How do you "measure" gamma? Is this 2.2-2.5 thing a source setting or something that is actually measured off the screen with a meter? My projector has Gamma on/off in firmware but it's not adjustable. I have a scaler with selectable ranges but not fully adjustable within those ranges.

garyfritz · Joined: 08 Apr 2006 Posts: 12088 Location: Fort Collins, CO

You measure it with a meter. It's a measure of brightness at each level from 10% to 100%, and then you find the power curve (roughly LumenOutput = IRE^gamma) that comes the closest. See e.g. this article.

CRTs may tend to fall in the 2.5 range but I've seen 2.0 - 2.4 in mine. Higher gamma values mean a darker image, because the lower and midrange IREs are much darker **in comparison to 100 IRE** than with higher gammas. So higher gamma values will cause dark areas and shadow detail to be much darker. See the curves in the article and you'll see what I mean.

Some CRTs have what they call gamma circuitry but I don't know what it does in each model. A "gamma booster" like the Moome boxes actually has the effect of *lowering* gamma by boosting the lumen levels at low IREs.

Boilermaker · Joined: 21 May 2006 Posts: 527

As Gary pointed out, gamma is the exponent in the relationship between the applied video voltage and the luminance output.

Look at the Luminance graph on your Calman or HCFR and you will see the desired (2.2) shown as a curved line. If gamma was 1.0, then this line would be straight at 45 degrees. The higher the gamma (exponent) the more curve there is and the slower the rise in luminance with respect to the video signal.

When I first started using one of the many analog low end gamma boost circuits, I said I would never do without one again. I have since changed my mind. I will now never do without a full equilisation system such as the Lumagen, DVDO Duo or the VideoEq. You can literally dial in whatever gamma you want from top to bottom. While it takes a good bit of time, it is well worth it. I have found that I prefer 2.2.

benareeno · Joined: 22 Mar 2006 Posts: 1614 Location: ottawa, canada

Would an htpc accomplish this too?

AFryia · Posted: Sat Jul 24, 2010 7:43 pm Post subject:

ilias · Joined: 20 Apr 2007 Posts: 116

My gamma in G70 and DVDO VP30 is 1,7, higher, make black scenes, grey!!!

benareeno · Joined: 22 Mar 2006 Posts: 1614 Location: ottawa, canada

I would think a lower gamma would make darker scenes grey....no?

ilias · Joined: 20 Apr 2007 Posts: 116

No! 1,8 or 1,9 gamma, from DVDO and no dark areas any more!!!

AFryia · Posted: Sun Jul 25, 2010 5:46 pm Post subject:

garyfritz · Joined: 08 Apr 2006 Posts: 12088 Location: Fort Collins, CO

A gamma of 1.7 would make things look very gray because low-IREs are much brighter, compared to 100IRE, than they're supposed to be. The lower the gamma, the "straighter" the 0-to-100IRE response curve gets, and the more washed-out the image looks.

_in_peace_ · Joined: 21 Jul 2009 Posts: 152 Location: Sweden

I wonder about the moome full hd. What gamma curve does it's simulates?

When i use it, i think Gamma 1.0 in powerstrip looks the best..

Boilermaker · Joined: 21 May 2006 Posts: 527

_in_peace_ · Joined: 21 Jul 2009 Posts: 152 Location: Sweden

Ok i think it's something wrong with my G2 settings that i now longer can get access to
(swaped digital boards A / B)

2 screen shots
http://web.comhem.se/~u73703191/IMG_4146.JPG
http://web.comhem.se/~u73703191/IMG_4151.JPG

Contrast 80
Brightness 50

bias:
42
27
Max

gain:
114
230
Max (+ alot unfocused)

+ ATI Avivo Video adjustments to get all levels (16-235)
Bright raised 4steps
Contrast lowered 6steps

(the nearest to get all 16-235 on my PS3 is to set the bright to 72 & contrast to 72. Some levels still missing though)

David_Web · Joined: 02 May 2007 Posts: 418 Location: Sweden

Powerstrip works in a different way than gamma even though it's called gamma.

1.0 is indeed a flat curve which means uncorrected. Same with any other app that modifies the LUT.

So what ilias means is probably the same type of correction which is NOT the same as final Gamma on screen.

Don't ask me why it works the wrong way around though. Makes no sense and never have.