Luminance & Grayscale - AVS Forum
Forum Jump: 
 
Thread Tools
post #1 of 7 Old 05-22-2012, 09:38 AM - Thread Starter
Advanced Member
 
wmwilker's Avatar
 
Join Date: Oct 2001
Posts: 917
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 33
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

Mike

wmwilker is offline  
Sponsored Links
Advertisement
 
post #2 of 7 Old 05-22-2012, 10:04 AM
AVS Special Member
 
PlasmaPZ80U's Avatar
 
Join Date: Feb 2009
Posts: 7,047
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 8 Post(s)
Liked: 186
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
PlasmaPZ80U is offline  
post #3 of 7 Old 05-22-2012, 10:10 AM
AVS Special Member
 
sotti's Avatar
 
Join Date: Aug 2004
Location: Seattle, WA
Posts: 6,585
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 12 Post(s)
Liked: 164
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.

Joel Barsotti
SpectraCal
CalMAN Lead Developer
sotti is offline  
post #4 of 7 Old 05-22-2012, 10:11 AM - Thread Starter
Advanced Member
 
wmwilker's Avatar
 
Join Date: Oct 2001
Posts: 917
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 33
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.

Mike

wmwilker is offline  
post #5 of 7 Old 05-22-2012, 10:19 AM
AVS Special Member
 
PlasmaPZ80U's Avatar
 
Join Date: Feb 2009
Posts: 7,047
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 8 Post(s)
Liked: 186
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).
PlasmaPZ80U is offline  
post #6 of 7 Old 05-22-2012, 10:24 AM
Advanced Member
 
Smackrabbit's Avatar
 
Join Date: Sep 2001
Location: Portland, OR, USA
Posts: 892
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2 Post(s)
Liked: 29
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.

Chris Heinonen
Senior Editor, Secrets of Home Theater and High Fidelity, www.hometheaterhifi.com
Displays Editor, AnandTech.com
Contributor, HDGuru.com and Wirecutter.com
ISF Level II Certified Calibrator, ReferenceHomeTheater.com
Smackrabbit is offline  
post #7 of 7 Old 05-22-2012, 10:32 AM - Thread Starter
Advanced Member
 
wmwilker's Avatar
 
Join Date: Oct 2001
Posts: 917
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 33
Thanks guys. That will give me something to work on for the next few days. I'll let you know how it works out.

Mike

wmwilker is offline  
Reply Display Calibration

User Tag List

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page


Forum Jump: 

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off