Gamma mia, here we go again, Gamma...

Gamma mia, here we go again, Gamma...

Post by Enterpros » Tue, 25 May 1999 04:00:00



I've turned off gamma correction in MAX. I've left my gamma on my monitor as
it is ie 2.2.


>For me, it's easiest to set Photoshop to preview in my monitor's native
>gamma + RGB and get maps looking o.k. there before working in Max. Then
I'll
>have a good idea what test renders will produce. I leave the Max gamma
alone
>since Photoshop's calibration is a bit more accurate, and double-correcting
>just confuses the issue. Once you've got your render, you can set Photoshop
>to simulate the conditions of display such as the web or print, and make
>your final corrections there. So my thinking is to work in just one color
>space so that the maps will look the same across different programs on my
>box which have different or no preview methods, and funnel everything thru
>Photoshop.

 
 
 

1. Monitor Gamma and Picture Gamma

There has been much discussion about Gamma on this list lately, a
topic of some confusion because there is Monitor Gamma and Picture
Gamma, and the two are not the same.

Theoretically, a perfect monitor could be built, where pure red shows
as pure red, pure green as pure green, etc.; however, because the
components that are used to build electronic equipment are highly
inaccurate, a perfect monitor is only theoretical.

The actual values of resistors, capacitors, and coils that go into a
piece of electronics vary greatly from their stated values. For
example, a higher-grade 3,000 ohm resistor can vary in value from
2,850 to 3,150 ohms. Standard resistors have a 10% tolerance. The
value of a capacitor can vary from +50% to -20% of its rated value.
Then there are factors such as stray capacitance, wire resistiance,
and inductance caused by the current to contend with.

So, while the design engineer says this circuit will do this, the
resultant application of that design might not, and they add variable
components to allow "tweaking". Instead of having a 3,000 ohm resistor
in some part of the circuit, they might use a 2,500 ohm one along with
an adjustable 250 to 750 ohm one.

The whole point of this is that your monitor is not going to be
perfect, even when it is new, and as it ages, the values of its
components (especially capacitors) will change.

Adjusting your monitor gamma is a way of tweaking it so pure red show
as pure red, etc. It also is used to establish a uniform grayscale.
This can be done completely independently of your graphics program,
and needs to be repeated periodically to compensate to component
aging.

On the other hand, if you use a program like Paint Shop Pro to adjust
the gamma value of a picture, you actually change the palette values
of that picture. One way to see this is to compare the palettes of a
picture at different gamma value adjustments (double-click on the
foreground or background color box or actually open the Jasc-format
palettes in a text editor).

Calibrating the gamma of your monitor just changes the way you view
pictures, not someone else's view. It's becoming the norm for PC
monitors to include gamma adjustment (I believe that it has been built
into Macs for some time, and UNIX). A good package will allow you to
set the values for red, green, and blue independently, along with
grayscale. If your monitor does not include this capability, then I
would search out one of the web sites that have been set up to handle
this, and not foing it from within a paint program.

I have found that I get a good match between my scanner, my printer,
and my monitor since I did the calibration.

Adjusting the gamma value of a picture can be useful for "tweaking"
its appearance, but remember that you are actually changing the colors
when you do so.

co

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