Gamma transfer function – ‘The way I see it’

R
Posted By
ronviers
Aug 1, 2006
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I have been trying to understand the gamma transfer function. I do not really have a mind for math but let me give it a shot anyway and maybe someone can tell me if I am heading in the right direction. Are the following statements true?

The prescription of my glasses, or contact lenses, can be thought of as representing my own personal gamma?

Gamma would be analogous to the 75ohm impedance matching transformer used to couple my coaxial cable to my TV.

The ‘gamma’ is a value used by the ‘gamma transfer function’ to couple two nonlinear devices?

Each time graphic information is moved from one device to another, linear or nonlinear, a gamma transfer function is applied.

The transfer from my camera to my raw utility would require a gamma value even if I am not aware of it.

The transfer of the same data from the raw converter to the color space of my editor would require another gamma.

The transfer of the same data from my working color space to my computer monitor uses a gamma transfer function – as define by my Adobe gamma control panel, i.e. the 2.2 PC standard.

The various methods of rendering intent – perceptual, absolute, relative and saturation – differ from one another by using a different gamma transfer function?

The ‘Levels’ and ‘Curves’ dialogs in CS2 are breakouts to the gamma transfer function.

Thanks,
Ron

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MR
Mike Russell
Aug 1, 2006
wrote in message
I have been trying to understand the gamma transfer function. I do not really have a mind for math but let me give it a shot anyway and maybe someone can tell me if I am heading in the right direction. Are the following statements true?

The prescription of my glasses, or contact lenses, can be thought of as representing my own personal gamma?

Gamma would be analogous to the 75ohm impedance matching transformer used to couple my coaxial cable to my TV.

The ‘gamma’ is a value used by the ‘gamma transfer function’ to couple two nonlinear devices?

Each time graphic information is moved from one device to another, linear or nonlinear, a gamma transfer function is applied.
The transfer from my camera to my raw utility would require a gamma value even if I am not aware of it.

The transfer of the same data from the raw converter to the color space of my editor would require another gamma.

The transfer of the same data from my working color space to my computer monitor uses a gamma transfer function – as define by my Adobe gamma control panel, i.e. the 2.2 PC standard.

The various methods of rendering intent – perceptual, absolute, relative and saturation – differ from one another by using a different gamma transfer function?

The ‘Levels’ and ‘Curves’ dialogs in CS2 are breakouts to the gamma transfer function.

With one or two exceptions, are of the above all more or less wrong, with the exception of the ones referring to color space transformations – these do use a gamma transfer function, but in most cases the gamma value is about the same, so even this is misleading.

There’s nothing magic about gamma. First you need a foundation in mathematics to know what a function is (mapping an input value to an output value), and what an exponential function is. If you used to know this, here is a good source for review, as well as basic knowledge. < http://www.wtamu.edu/academic/anns/mps/math/mathlab/col_alge bra/col_alg_tut5_ratexp.htm>

The gamma transfer function is defined as f(x) = x **(1/gamma) . Once you have that as your starting point, you can be on firm ground as far as generalizations about what gamma does and how it is used. For example, levels and curves do not use an exponential function. So they are not examples of the gamma transfer function.


Mike Russell
www.curvemeister.com/forum/
R
ronviers
Aug 1, 2006
Mike Russell wrote:

There’s nothing magic about gamma. First you need a foundation in mathematics to know what a function is (mapping an input value to an output value), and what an exponential function is. If you used to know this, here is a good source for review, as well as basic knowledge. < http://www.wtamu.edu/academic/anns/mps/math/mathlab/col_alge bra/col_alg_tut5_ratexp.htm>
The gamma transfer function is defined as f(x) = x **(1/gamma) . Once you have that as your starting point, you can be on firm ground as far as generalizations about what gamma does and how it is used. For example, levels and curves do not use an exponential function. So they are not examples of the gamma transfer function.

Got it. I will get back to work. Thanks for the link and th information.

Brgds,
Ron
J
Jim
Aug 2, 2006
wrote in message
I have been trying to understand the gamma transfer function. I do not really have a mind for math but let me give it a shot anyway and maybe someone can tell me if I am heading in the right direction. Are the following statements true?

The prescription of my glasses, or contact lenses, can be thought of as representing my own personal gamma?

Gamma would be analogous to the 75ohm impedance matching transformer used to couple my coaxial cable to my TV.

The ‘gamma’ is a value used by the ‘gamma transfer function’ to couple two nonlinear devices?

Each time graphic information is moved from one device to another, linear or nonlinear, a gamma transfer function is applied.
The transfer from my camera to my raw utility would require a gamma value even if I am not aware of it.

The transfer of the same data from the raw converter to the color space of my editor would require another gamma.

The transfer of the same data from my working color space to my computer monitor uses a gamma transfer function – as define by my Adobe gamma control panel, i.e. the 2.2 PC standard.

The various methods of rendering intent – perceptual, absolute, relative and saturation – differ from one another by using a different gamma transfer function?

The ‘Levels’ and ‘Curves’ dialogs in CS2 are breakouts to the gamma transfer function.

Thanks,
Ron
Once upon a time, when television was just getting under way, the engineers observed that the signal to the tube was a voltage. However, the light output from the phospors is dependent on the power of the signal. Hence without some kind of compensation, the picture from the tube would not be close to the original.

There was a choice between placing a compensation circuit in every TV set or in placing much the same circuit in the TV cameras. There being far fewer TV cameras, it was more cost effective to install the circuit in the cameras.

This circuit compensates for the difference between a voltage and the corresponding power by imposing the gamma correction to the signal as output by the cameras.
Note that it is not necessary to put the circuits in the cameras; one could just as easily (and possibly more cheaply) install the special circuitry in the transmitters.

Another poster has shown the equation which this cercuitry imposes. Jim

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