Projector Gamma - AVS Forum
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post #1 of 7 Old 02-01-2013, 07:50 AM - Thread Starter
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What can cause projector gamma to hang around 1.3. I have seen this on both JVC's I have own and a LG. My new 4810 avg gamm is 1.5 out of the box on all modes, cinema, custom, animation etc...It's very difficult to get a 2.3-2.4 gamma.. Any Ideas


Note that when I VP is use to compensate for the low gamma numbers, bring it to 2.3-24, the picture is "polorized".
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post #2 of 7 Old 02-01-2013, 08:02 AM
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What device are you using for input? Could be a level issue with the device. I have no problem getting 2.2 out of my 7 year old HC3000 using my C6.
You may want to try measuring it using the component connection if your input device has component to see if it remains the same.. Also try a different resolution. If things change, you HDMI output could be the issue.
One other thing, do you put up a 100% pattern and adjust the meter on the tripod to achieve the highest light output prior to your measurements?
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post #3 of 7 Old 02-01-2013, 08:16 AM - Thread Starter
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Quote:
Originally Posted by airscapes View Post

What device are you using for input? Could be a level issue with the device. I have no problem getting 2.2 out of my 7 year old HC3000 using my C6.
You may want to try measuring it using the component connection if your input device has component to see if it remains the same.. Also try a different resolution. If things change, you HDMI output could be the issue.
One other thing, do you put up a 100% pattern and adjust the meter on the tripod to achieve the highest light output prior to your measurements?

Using a OPPO BR player.
Yes alway position the meter to get the highest FL prior to calibrating.
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post #4 of 7 Old 02-01-2013, 08:17 AM
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I've been measuring my very similar X35 with and without my Lumagen in the loop. I set the custom gamma to 2.3 default and the Lumagen only had to make very small adjustments to give me a 2.25 targeted gamma. I'm using the following settings as a base if it helps:

HDMI set to Superwhite.
Brightness to 0
Contrast to +5 (clipping above 245 on AVS test patterns)
All other controls at 0
Colour space Standard
Colour temp custom based on 7000K (RGB offsets left at 0 RGB gains set to give <3dE at 100% because I use the Lumagen for the detailed adjustments)

I use an Oppo BDP-93 player and he AVS HD709 test disc for the basic set up.

Zooming: Been there, done that, bought the lens...
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post #5 of 7 Old 02-01-2013, 08:41 AM - Thread Starter
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Quote:
Originally Posted by Kelvin1965S View Post

I've been measuring my very similar X35 with and without my Lumagen in the loop. I set the custom gamma to 2.3 default and the Lumagen only had to make very small adjustments to give me a 2.25 targeted gamma. I'm using the following settings as a base if it helps:

HDMI set to Superwhite.
Brightness to 0
Contrast to +5 (clipping above 245 on AVS test patterns)
All other controls at 0
Colour space Standard
Colour temp custom based on 7000K (RGB offsets left at 0 RGB gains set to give <3dE at 100% because I use the Lumagen for the detailed adjustments)

I use an Oppo BDP-93 player and he AVS HD709 test disc for the basic set up.

Kelvin,

Have you noticed that the offtets have no affect? Or maybe it's just my unit. I can crank them from hi to lo and no changes. I do notice that the color tone adjust the offsets.. Again this could just be my unit.
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post #6 of 7 Old 02-01-2013, 08:55 AM
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I just don't use the offsets: If you raise them above 0 then it raises the black floor and if you lower them below 0 then it can cause black crush. While I use the Lumagen's controls (21 points greyscale including 0) you could use the custom gamma to adjust the RGBs at the various % levels instead.

Zooming: Been there, done that, bought the lens...
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post #7 of 7 Old 02-01-2013, 10:58 AM
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I think the original poster meant the images were posterized when he used a video processor to try to improve gamma...

First, Gamma should be 2.2-2.3 because that what is used in studios that create the masters for Blu-ray discs... I use 2.25. Setting gamma to 2.3 to 2.4 makes everything in the midtones (35%-75%) too dark.

Posterization indicates that you are not getting 8-bits of resolution... something in the image path is causing a loss of bits in the images. This can happen when the video processor settings are too severe or when the projector settings are too severe. Very large setting changes stress the digital video processing path, though the more headroom there is in the video data path, the less likely this is to happen. There are surprisingly large numbers of video displays that have 10-bit video paths... and that would be OK if those bits were all used effectively, but I've worked on some Toshiba models (for example) where adjusting a control more than +/-3 out of a +/- 15 setting range causes posterization. On the other hand, Samsung is the only brand I know of that has an 18-bit internal data path and I've never seen posterization develop on a Samsung TV even with fairly large calibration settings.

When posterization is an issue, the best thing to do is to fix some of the problem using the settings in the projector and fix the remainder of the problem with the video processor... that way, neither device is pushing the adjustment envelope too much. You could also get a better video processor that can handle large setting moves without creating the posterization problem.

Next, the settings you pick in the projector could be causing the problem to happen much sooner than it should happen... you must make sure you are not clipping steps below 235 using an appropriate test pattern (I prefer a pattern with digital steps from 220-255... that kind of pattern allows you to see if you are clipping... if you are clipping on the white end of the spectrum, posterization is much more likely. You must be using the best user menu settings in the projector to avoid posterization.

Finally, I have never seen a situation where a projector and TV using completely different display technologies have similar (poor) gamma measurements. And that makes me wonder: 1) if you are doing the measurements properly; 2) if the user menu settings are the best possible settings; 3) if there is something you are not understanding about the measurement results (graphs, meaning of data, etc.). Obviously you are seeing the posterization problem after fixing gamma... but I'm not so sure that you are making the measurements properly or perhaps not interpreting the measurements properly and that is leading you to make bad adjustments. I do not remember ever seeing a JVC projector with 1.3 gamma... 1.7 or 1.8, yes, I have seen that in some JVC models 4 or 5 or 6 years old, but not in newer JVC projectors. I don't work on LG displays (nobody has ever called for a calibration) so I can't say from personal experience whether they have problems with low gamma, but I have never read a post from anyone saying that their LG TV's gamma was 1.3 and they couldn't make it higher. Both of those things make me wonder if there's something about the measurements or about the understanding of the measurement results that is giving a false result.

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