dear all,

I did try to find the gamma factor for my flatscreen monitor (Dell standard
15') connected to Matrox GForce2 400 video card, folllowing the procedure
outlined in the manual.
It did not work out as I expcted, in particular the step to lower brightness
till invisible does not work.
I assume there is a different procedure for flatscreens, or it may be
obsolete entirely, the monitor doing its own gamma correction. If so, what
'assumed gamma' should I use for this combination, or should I skip the
assumed gamma line entirely?

Frans Verbaas

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In article <3dc84fa9@news.povray.org>,
 "Frans Verbaas" <not### [at] freelernl> wrote:

> I assume there is a different procedure for flatscreens, or it may be
> obsolete entirely, the monitor doing its own gamma correction. If so, what
> 'assumed gamma' should I use for this combination, or should I skip the
> assumed gamma line entirely?

LCDs don't have the same kind of gamma curve as CRTs, as I recall the 
curve of LCD screens is more of an S shape. I don't know what settings 
are the best, it would depend on the particular screen. I wouldn't be 
too surprised if it did the compensation in the monitor, with a result 
like it had a perfectly linear gamma.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

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I use Display_Gamma=2.3 for my notebook LCD. That seemed the closest match
using the usual CRT method. I can't raise and lower contrast and brightness,
except only within certain constraints. Well, I could do brightness from
black to white in the display properties but to me that's a different thing,
like adjusting away from the default gamma to then check gamma.

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> I use Display_Gamma=2.3 for my notebook LCD.

Really? My laptop LCD screen has a gamma very close to 1.

 - Slime
[ http://www.slimeland.com/ ]

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"Slime" <slm### [at] slimelandcom> wrote in message
news:3dc88605$1@news.povray.org...
> > I use Display_Gamma=2.3 for my notebook LCD.
>
> Really? My laptop LCD screen has a gamma very close to 1.

Well, yes, based on the chart of gray shaded bars (made up of thin lines)
anyway. Perhaps about the worst way to check but I could look from far
enough away to get the shades looking the way I thought they should.

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> > Really? My laptop LCD screen has a gamma very close to 1.
>
> Well, yes, based on the chart of gray shaded bars (made up of thin lines)
> anyway. Perhaps about the worst way to check but I could look from far
> enough away to get the shades looking the way I thought they should.


Actually, I never found that test very successful. The reason I believe it's
close to 1 is that over the summer, when I tested my web site on my home
computer (with a regular monitor), the colors were significantly darker than
I had wanted them to be. By gamma correcting the colors, I made them look
right on the computer monitor (although a little washed out on my LCD). The
gamma correction I did assumed that my LCD screen had a gamma of 1, and
worked out just about perfectly.

Other similar experiences also backed it up.

 - Slime
[ http://www.slimeland.com/ ]

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Frans Verbaas wrote:
>
> I did try to find the gamma factor for my flatscreen monitor (Dell standard
> 15') connected to Matrox GForce2 400 video card, folllowing the procedure
> outlined in the manual.

The procedure works only if the display does CRT/sRGB emulation.
I don't know if normal consumer level models do this but one Sony
display has gamma menu item for which the manual doesn't give a
clear explanation for. Could be CRT emulation or not.

Browse the menus, manual and driver settings to find out for an
emulation option.

Uncorrected LCD transfer curve is not suitable for graphics work
so if a display is marketed as such it should be able to emulate
CRT gamma. If not, get your money back.


> what 'assumed gamma' should I use for this combination, or should
> I skip the assumed gamma line entirely?

Use whatever floats your boat. assumed_gamma 1 is recommended since
it reproduces the scene intensities linearly (on CRT display). Set
Display_Gamma instead.

If the display doesn't do CRT emulation, compare to a CRT display
with known gamma and make an educated guess or just leave it at
the default Display_Gamma=2.2. Publishing your images, not only
povray images,  will be problematic though, as most displays are
CRTs or emulate one.


_____________
Kari Kivisalo

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I've been wondering about this question myself... In the end, I decided that
my laptop's LCD display is just *waaaaaaaaay* too unsaturated. No matter
what angle I view it from, part of the screen is too dark and another part
is too bright (and yet another part is in inverted colour). So I guess CRT
is the only way to go if I'm POVing...

Andrew.

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Well, it seems there is little known about this.
My problem was that I had to have a picture plotted on an A2 sized poster
for an exhibition, and, also in view of the cost involved with any remakes,
I did not want the colors to change. Hence I submitted my file to the
printshop with a sample A4 sized print of the right tone and brightness.
They did any color adjustment needed for their plotter to match my colors.
Thank you Mr. Kinko's!

Thank you all for your input

Frans

"Frans Verbaas" <not### [at] freelernl> schreef in bericht
news:3dc84fa9@news.povray.org...
> dear all,
>
> I did try to find the gamma factor for my flatscreen monitor (Dell
standard
> 15') connected to Matrox GForce2 400 video card, folllowing the procedure
> outlined in the manual.
> It did not work out as I expcted, in particular the step to lower
brightness
> till invisible does not work.
> I assume there is a different procedure for flatscreens, or it may be
> obsolete entirely, the monitor doing its own gamma correction. If so, what
> 'assumed gamma' should I use for this combination, or should I skip the
> assumed gamma line entirely?
>
> Frans Verbaas
>
>

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