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Greyscale calibration gamma problem

 
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krisgs



Joined: 21 Jun 2010
Posts: 7



PostLink    Posted: Mon Jun 21, 2010 6:38 am    Post subject: Greyscale calibration gamma problem Reply with quote


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Hi,
I read the the greyscale calibration guide for dummies recently and find it very good, now I can even see 3D movies without ghost effects. I have a <sony bravia klv serie and I accesed the hidden menu to calibrate and so on all is ok.
Now the calibration is done with my spyder2pro and all went fine.
The only thing that isn't good is my gamma.
My gamma should be somewhere around the 2.2 like the guide tells but I only get 1,6-1,8.
Wat can I do to improve this.
I'll try to post The before after files from hfcr here too

In the normal menu of the Sony I can do gamma correction from 0 to 5.
It is set to 0 and if I rase the number then the picture gets lighter, is this the thing I need and is this as called that gamma booster or so ?

thx very mutch
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Rolls-Royce



Joined: 30 Sep 2007
Posts: 288
Location: Victorville, CA


PostLink    Posted: Mon Jun 21, 2010 4:53 pm    Post subject: Reply with quote

A 1.6-1.8 gamma is lighter than 2.2, so raising the gamma control isn't what you need to do. What is your Y reading at 100 IRE or 100% stim? In most displays, the "contrast" or "picture" control also pulls up "brightness" (black level) as you boost it, driving your gamma number down. They do interact. So, if you have the contrast/picture control set high, it usually will pull up the black level enough to wash out the picture unless you go back and readjust it. I'd suggest rechecking your test pattern source's brightness and contrast patterns, and check the 100 IRE/% luminance with your meter. 30-35 ft/L is a good starting point.
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krisgs



Joined: 21 Jun 2010
Posts: 7



PostLink    Posted: Mon Jun 21, 2010 5:19 pm    Post subject: Reply with quote

I've posted the readings normal in the thread as rar file,
The calibrated readings at 100 IRE:

cd/m2:152,75
FTL: 44,584
T : 6544
X : 145,516
Y : 152,745
Z : 167,918
R : 153,046
G : 152,485
B : 154,437
x : 0,312
y : 0,328
z : 0,360
L : 100
a : 0,4
b : - 0,6
L : 100
C : 0,7
H : 301,4

thx a lot to answer so fast
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Rolls-Royce



Joined: 30 Sep 2007
Posts: 288
Location: Victorville, CA


PostLink    Posted: Mon Jun 21, 2010 6:43 pm    Post subject: Reply with quote

That 44.5 ft/L at 100 IRE is a touch high, IMHO. Others here may disagree with this. I personally have my displays set for about 80 cd/m2 at 100%, but 100 cd/m2 would be a good intermediate point. Unless you're watching in a brightly-lit room, you probably don't need all that light output anyway.
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krisgs



Joined: 21 Jun 2010
Posts: 7



PostLink    Posted: Wed Jun 23, 2010 5:41 am    Post subject: Reply with quote

OK, But has that something to do with the gamma ? And my room isn't really dark, what difference does gamma 1.7 do in opposite with 2.2 ?
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Rolls-Royce



Joined: 30 Sep 2007
Posts: 288
Location: Victorville, CA


PostLink    Posted: Wed Jun 23, 2010 7:43 am    Post subject: Reply with quote

krisgs wrote:
OK, But has that something to do with the gamma ? And my room isn't really dark, what difference does gamma 1.7 do in opposite with 2.2 ?


Yes. If you run 100%/IRE at high luminance, it can also pull your black level up and then you will have a washed-out image with a gamma below 2. Gamma numbers go in the reverse direction of luminance readings: as your lower end gets brighter, the gamma number goes DOWN. As your lower end gets darker, gamma numbers go UP. Got it? Smile

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krisgs



Joined: 21 Jun 2010
Posts: 7



PostLink    Posted: Wed Jun 23, 2010 8:18 am    Post subject: Reply with quote

OK,got it I think, and that my detail in the dark parts are not like I want is this reason to then ? The low gamma ? So I must now set the ftl to 30 and recalibrate for now ?
So , if this is correct , I'll post my new readings after I done it
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Rolls-Royce



Joined: 30 Sep 2007
Posts: 288
Location: Victorville, CA


PostLink    Posted: Wed Jun 23, 2010 4:28 pm    Post subject: Reply with quote

krisgs wrote:
OK,got it I think, and that my detail in the dark parts are not like I want is this reason to then ? The low gamma ? So I must now set the ftl to 30 and recalibrate for now ?
So , if this is correct , I'll post my new readings after I done it


You don't have to set 100 IRE to 30-35 ft/L. It's just a general recommendation. If you are watching in a room that has large windows or is otherwise brightly lit most of the time, you might want more light output than that from the display to help overcome the room's lighting. With my own displays, however, I've found that running them at higher light outputs makes it tougher to achieve a good 2.2-2.5 gamma. I usually shoot for a gamma of 2.25-2.3. Our living room is brightly lit by natural sunlight in the late afternoon, and that gamma range keeps shadow detail visible then without it being too light when the room is darker (mornings and nights).

In any case, when you finish a grayscale session, you should always go back and recheck your source's brightness and contrast patterns since adjusting gray balance will affect them as well.

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krisgs



Joined: 21 Jun 2010
Posts: 7



PostLink    Posted: Wed Jun 23, 2010 6:35 pm    Post subject: Reply with quote

EUCHM, so what must I do now then ???
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krisgs



Joined: 21 Jun 2010
Posts: 7



PostLink    Posted: Thu Jun 24, 2010 7:55 pm    Post subject: Reply with quote

PFFFT<<, i think i am doing something wrong, can't get higher gamma then 1,7
is this correct:
100% read ftl = 30,...
check Y = 104,...
then
10% set brightness to Y= 104,... * 0,0065 = let's say 0,7
so then I must set ftl at 10% to 0,7 eh correct ?
or must i set Y to 0,7 ? Because if i do so i don't see the bars +2 and +4% grey anymore
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Rolls-Royce



Joined: 30 Sep 2007
Posts: 288
Location: Victorville, CA


PostLink    Posted: Sat Jun 26, 2010 2:33 am    Post subject: Reply with quote

Digital displays sometimes have a problem with black levels in that they tend to come out of black pretty fast (they are brighter than they should be at low IREs). Digital Video Essentials' HD Basics BD mentions this in its section about setting brightness. You have an artistic choice to make here: adjust 10% to its proper luminance and lose a little very-near-black shadow detail, or run 10% luminance a bit higher to be able to see it. Try it both ways while watching a DVD or BD you are familiar with and see which you like best.
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krisgs



Joined: 21 Jun 2010
Posts: 7



PostLink    Posted: Wed Jul 07, 2010 5:35 am    Post subject: Reply with quote

OK, GONNA TRY IT

THX
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