Re: Gamma (Andrew Rodney)
Re: Gamma (Andrew Rodney)
- Subject: Re: Gamma (Andrew Rodney)
- From: MSP Graphics <email@hidden>
- Date: Wed, 25 Jul 2007 13:20:21 -0700
The relationship between input and output of devices, such as
printers,
scanners, and digital cameras, often does not follow a simple gamma
curve.
The values are far more complex and can¹t be described using this
simple
formula. What we are talking about here is a concept that should be
described as the device¹s TRC, not as the device¹s gamma.
Therefore, all
devices have a TRC but few TRC curves are gamma curves! Note that many
devices (LCD displays, scanners, etc.) map their original TRC to a
TRC that
follows the gamma formula. These devices appear to the color
management
system as following the gamma formula. When describing the response
of a
system, the correct statement would be, ³My scanner has a TRC of
gamma 1.8,²
instead of, ³My scanner has a 1.8 gamma.² It seems like silly
semantics but
it¹s useful to understand.
Andrew Rodney
http://www.digitaldog.net/
To simplify a bit: It is common for scientists to do a bit of "curve-
fitting" to describe a system's response to some input/stimulus as a
mathematical function--even when it is only an approximation. It was
found that the response of certain devices (TV monitors, for example)
could be plotted as a curve that looked a lot like a gamma function,
which is some constant raised to that power given by the "gamma"
number. So a number raised to the power of 2.5, for example, will
yield a steeper curve than the same number raised to the power of
1.8. Thus a monitor producing a "gamma" of 2.5 will give a more
abrupt change in light output that one with a gamma of 1.8 given the
same input signal increase, and would thus have higher image
contrast. But as Andrew just said, the actual response curve in
question may be quite different from a true gamma curve, so it's best
to be cautious when comparing the "gammas" of different systems and
regard "gamma" as only an approximate and relative measure of system
contrast.
Mike Strickler
MSP Graphic Services
423 Aaron St. Suite E
Cotati, CA 94931
ph. 707.664.1628
fx. 707.939.4542
www.mspgraphics.com
_______________________________________________
Do not post admin requests to the list. They will be ignored.
Colorsync-users mailing list (email@hidden)
Help/Unsubscribe/Update your Subscription:
This email sent to email@hidden