Gamma correction

On a sunny day (Sun, 25 Jan 2009 11:00:41 -0800 (PST)) it happened snipped-for-privacy@gmail.com wrote in :

Display a testcard? Test pattern?

Yyes, modern displays sometimes also modulate the back light. But modulating the background for _this_ display works for the _whole_ display. So in this case it does not help you much if the pattern is anything other then a completely even surface...

We are all new, the field changes almost faster then light.

Do you know any link and/or tutorial about its correct use?

Ok

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

:-)

On a sunny day (Sun, 25 Jan 2009 23:43:14 -0800 (PST)) it happened snipped-for-privacy@gmail.com wrote in :

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.

The way I make a test pattern is write some code, the ramp is easy, then display it on the PC monitor using a normal graphics viewer.

A good and easy format is the ppm format to make a pattern, most graphics programs can read it and convert it to any other format.

On Linux man ppm Use imagemagick suite 'convert' to convert it to any other format. Use 'display' to display it.

The ppm format is just the values for red green and blue in ASCII:

display.

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? That can only be done if there is a LED behind each square. And there is not in this display.

waveform,

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

display.

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.

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....

Ok, i understand now, but i'm not able to apply this answer in this function

On a sunny day (Tue, 27 Jan 2009 13:09:18 -0800 (PST)) it happened snipped-for-privacy@gmail.com wrote in :

darker?

I am not sure, but I think all that [function] says is that if your backlight is brighter, then white will be brighter :-)

So, basically if you backlight is off (dark) there is no white and you see nothing. this all assumes a transmissive panel. In a reflective or partly reflective panel you would still get a picture without any backlight (for b = 0).