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Luminance & Grayscale

post #1 of 7
Thread Starter 
Is there a desired average percentage of luminance between grayscale steps? Would too great a jump in luminance between steps cause posterization?
I think I'm seeing a hint of posterization on some sources but my grayscale looks pretty good across the board. I'm trying to dial it in and I thought if there were some numbers I could use as a reference it would be much easier.
Thanks
post #2 of 7
Quote:
Originally Posted by wmwilker View Post

Is there a desired average percentage of luminance between grayscale steps?
Thanks

yes, and its called gamma and it's also affected by the dynamic range of the display
post #3 of 7
Quote:
Originally Posted by wmwilker View Post

Is there a desired average percentage of luminance between grayscale steps? Would too great a jump in luminance between steps cause posterization?
I think I'm seeing a hint of posterization on some sources but my grayscale looks pretty good across the board. I'm trying to dial it in and I thought if there were some numbers I could use as a reference it would be much easier.
Thanks

There are many different formulas that seek to quantify what qualifies as a noticeable difference between colors. JND is what's used in the medical field and it has a pretty elaborate formula to determine the threshold of the next step from the previous step based on the luminance level.

But the gamut saturation level are closely connected to your gamma. So you can't really modify the step sizes without also changing your gamut saturation.

In the end all you can really do is choose an appropriate gamma target and luminance target. After that it's up to the source to minimize banding/posterization. All these streaming/on-demand low bandwidth source will frequently show posterization because it's encoded in the content.
post #4 of 7
Thread Starter 
Quote:
Originally Posted by PlasmaPZ80U View Post

yes, and its called gamma and it's also affected by the dynamic range of the display

Thanks, even though I feel stupid about the question.
If grayscale and gamma are virtually flat why would I have the hint of posterization? It is a little more obvious in cable source than in BR but it is still there.
post #5 of 7
Quote:
Originally Posted by wmwilker View Post

Thanks, even though I feel stupid about the question.
If grayscale and gamma are virtually flat why would I have the hint of posterization? It is a little more obvious in cable source than in BR but it is still there.

http://www.spearsandmunsil.com/artic...stcontrol.html

http://www.spearsandmunsil.com/artic...epatterns.html

These articles talk a bit about banding/posterization/contouring with respect to the brightness and contrast controls. Banding can also result from multi-point grayscale controls (like 10 or 20 point grayscale controls) and CMS controls. Other times your TV has it from the very beginning and you can't fix it or perhaps even reduce it (though you want try to minimize it as much as possible anyway).
post #6 of 7
Quote:
Originally Posted by wmwilker View Post

Thanks, even though I feel stupid about the question.
If grayscale and gamma are virtually flat why would I have the hint of posterization? It is a little more obvious in cable source than in BR but it is still there.

Some controls just aren't implemented well and can only be adjusted so much before posterization kicks in, and some can be adjusted as much as you want with no issue. For example, on the JVC X30 this year, the gamma presets all worked great, but if I used the gamma fine tuning, posterization set in as soon as I adjusted it off the defaults. I've seen the same behavior on other projectors as well, so it's not a JVC issue only.

Try setting up a second memory with no adjustments done and see if you get the posterization or not. If you don't, then you can start to copy settings from the other preset, one at a time, starting with the basic ones first, until you can see if it sets in or not. Slow and tedious, but you could figure out what is causing it.
post #7 of 7
Thread Starter 
Thanks guys. That will give me something to work on for the next few days. I'll let you know how it works out.
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