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Gamma correction

I have this small lcd display
http://www.sharpsme.com/Page.aspx/europe/en/part/LQ043T3DX02/
and i've read something about gamma correction (correct me if i'm
wrong)....In lcd display gamma correction is performed by lcd drive
circuit: it applies an ac voltage in lc cell to obtain desidered
Transmittivity/voltage characteristics (transmittivity/voltage without
correction is a sigmoidal fuction). How can i know corrected function?
is it linear or power-law (as crt)?
Another question:
i've read this relationship:
backlight_luminance*transmittivity=output_luminance. If transmittivity
is a linear function, when is more useful a contrast change respect to
a backlight_luminance change? Backlight_luminance change is more power
saving, so i can obtain the same output result with less power...or
not?
Thanks for the help (i'm new in this field, so excuse me for the
questions)
 
Display a testcard?
Test pattern?

Do you know any link and/or tutorial about its correct use?
Yyes, modern displays sometimes also modulate the back light.
But modulating the background for _this_ display works for the _whole_ display.
Ok

So in this case it does not help you much if the pattern is anything other
then a completely even surface...

I don't undestand: the output effect should't be the same?
We are all new, the field changes almost faster then light.

:)
 
J

Jasen Betts

Jan 1, 1970
0
Well, I dunno what you know, but it is easy to test with a horizontal ramp waveform,

So you make a .gif or something with this horizontally:
.
. |
. |
. |
. |
. |
. |_

If it looks like a linear ramp on that LCD, then you need to correct it.


do a linear ramp and a black & white Burkes dither of a linear ramp adjacent in the same
image adjust gamma until they agree.
 
Q

qrk

Jan 1, 1970
0
Do you know any link and/or tutorial about its correct use?


I don't undestand: the output effect should't be the same?


:)

There are many web sites with gamma charts. This site gives info on
gamma and has a few charts about midway through the article. Look
around enough and you'll find different types of charts.
http://www.normankoren.com/makingfineprints1A.html

If you need to adjust gamma on your monitor, you'll probably need to
do it though the graphics card driver. I'm finding that some LCD
panels don't do brightness and contrast properly. Most modern graphics
drivers have gamma adjust burried somewhere in there menu structure.
 
Thanks everybody for the help....
In an LCD all pixels are driven at the same time (sort of) in a field.
So imagine you have a pattern of black and white squares.
How is modulating the backlight going to help you display that?
I mean in the sense of making the white ones brighter and the black ones darker?

Ok, i understand now, but i'm not able to apply this answer in this
function
http://img401.imageshack.us/img401/1339/functionrq3.jpg
with b[0;1] =backlight factor=luminance/maximum luminance
If contrast changes, dt(x)/dx changes....what happens if backlight
varies?I shoud obtain (in agreement with your answer) an offset in
luminance function, but i'm not able to display it....
Thanks
 
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