[Christopher B]

This may be a stupid question, but I wondered how contrast ratio effects gamma.


I have a Samsung HL61A750. The "recommended" gamma setting for movie mode is -3. When using the Avia squinting method with the gamma test it shows -3 produces about a 2.2 gamma. After setting contrast and brightness and comparing various scenes, the 2.2 setting causes loss of shadow detail. When the -2 gamma setting is used, it produces about 1.8 and shows more shadow detail.


Does the contrast ratio of the TV effect the usable gamma range, and is it normal to lose some shadow detail with a 2.2 or 2.5 gamma, or is it due to the limitations of the television?


I know that calibration is meant to set up a TV to a certain standard and that ultimately I need to calibrate for me. But I wondered if the standard includes this loss of detail, or when my set is calibrated close to the standard, it is not able to produce the "best" results.


I know someone will just ask if I am happy with my picture and that if I am, who cares about what gamma is set at. I ask simply because I am curious!


Thanks

 

[umr]



Quote:
Originally Posted by Christopher B /forum/post/15495341


This may be a stupid question, but I wondered how contrast ratio effects gamma.


I have a Samsung HL61A750. The "recommended" gamma setting for movie mode is -3. When using the Avia squinting method with the gamma test it shows -3 produces about a 2.2 gamma. After setting contrast and brightness and comparing various scenes, the 2.2 setting causes loss of shadow detail. When the -2 gamma setting is used, it produces about 1.8 and shows more shadow detail.


Does the contrast ratio of the TV effect the usable gamma range, and is it normal to lose some shadow detail with a 2.2 or 2.5 gamma, or is it due to the limitations of the television?


I know that calibration is meant to set up a TV to a certain standard and that ultimately I need to calibrate for me. But I wondered if the standard includes this loss of detail, or when my set is calibrated close to the standard, it is not able to produce the "best" results.


I know someone will just ask if I am happy with my picture and that if I am, who cares about what gamma is set at. I ask simply because I am curious!


Thanks

Your method for setting gamma is flawed.


You should measure with a light meter and also look at images to see what works the best. The Avia squint method is very poor. Brightness and contrast should also be checked at every setting. You should also note that Samsung is notorious for faulty gamma curves that can measure well and look awful. The visibility of near black information will depend on the set and your room lighting. A higher gamma by definition will reduce the visibility of near black information. In reality this information should not be very obvious. If you are going for a theater look in a dark room the gamma should be fairly strong if the display can handle it. It all comes down to how you plan on using your display and the displays capability. Only the absolute best displays can handle a gamma higher than 2.2 without introducing other problems.


When it comes to gamma the lower 10% is the most important and unfortunately the hardest to measure well. It is best to judge this with real images to make sure things worked well. Dynamic black levels will also play havoc with gamma and should be considered when calibrating any display.

 

[sotti]

People talkt about gamma like your set has one gamma setting, but you don't


Every point from black to white generally has a slightly different response in respect to gamma and at each point you can calculate the response in respect to a gamma curve that would travel through it.


So your "2.2" gamma may actually start off at 2.6 below 5IRE ramp up to 2.2, then tail off to 1.9 at the high end.


But if -3 is the sets default for movie mode it's a safe bet that's ballpark where gamma should be, if blacks are getting crushed, turn up the brightness.


Don't even look at a pattern based gamma correction, squinty eyes will just give you a headache.

 

[Christopher B]

Thanks guys!


I am going to go take an aspirin now since I have a headache from all the squinting!

 

[BeachComber]



Quote:
Originally Posted by sotti /forum/post/15496829


People talkt about gamma like your set has one gamma setting, but you don't


Every point from black to white generally has a slightly different response in respect to gamma and at each point you can calculate the response in respect to a gamma curve that would travel through it.


So your "2.2" gamma may actually start off at 2.6 below 5IRE ramp up to 2.2, then tail off to 1.9 at the high end.

Not if you have a professional meter. I cannot think of anyone who would think the numbers you gave are acceptable, except, I guess, for you.

 

[sotti]



Quote:
Originally Posted by BeachComber /forum/post/15504949


Not if you have a professional meter. I cannot think of anyone who would think the numbers you gave are acceptable, except, I guess, for you.

Did I say those measurements where good?

No.


What I was saying if from some eye pattern test, you have no idea what your gamma curve actually looks like.


My point exactly was that it's much more important to get your brightness up so you don't crush your blacks than to keep them low because that is what you think the optical gamma pattern is telling you to do.


I would appreciate it if you would stop treating me like I'm ignorant and actual read my posts.

 

[jarrod1937]

I think sotti is saying that the visual patterns can lead to a perception of the "average" gamma value, though even then its probably inaccurate. However, the average gamma, while possibly even being deadon 2.22 (or whatever value is best for your environment), you need a meter to see what the complete gamma curve is like. After all, you can get a nice perfect average gamma of 2.22 but have your blackend crushed and your white end washed out. An actual plot of all points of the greyscale, or multiple numbers at different parts of it, are needed. A single number cannot describe your gamma.