Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.graphics.apps.gnuplot > #641

Re: set palette cubehelix

Followups directed to: comp.graphics.apps.gnuplot

Show all headers | View raw

sfeam wrote:
> 
>> According to http://en.wikipedia.org/wiki/Gamma_correction I would
>> say that mine interpretation is correct (see the example photograph
>> of the lady in the water). But the Wikipedia article might be wrong
>> as well.
> 
> The Wikipedia article is very confusing as it does not, that I can
> see, define the basic quantity V used in the fundamental equation
> given at the top of the article:
> 
> Vout = Vin ** gamma
> 
> For any quantity V that increases with brightness (e.g. amplitude,
> intensity, brightness) it is clear that gamma > 1 increases
> brightness. And yes, it seems to me that the images on the Wikipedia
> page are mis-described.

Upon re-reading, I now see that the Wikipedia article has lifted
that equation from the section on CRT voltage response.  So in that
context V is a normalized voltage that runs from 0->1, and indeed
gamma>1 means that the image displayed by the CRT is darker than
would be the case for linear response.  So the article is consistent
with itself, but still it conflates the gamma of the CRT with that
of the algorithm used in image processing to correct for it.
A CRT with gamma > 1 is dark, so in order to correct for this you
must brighten the image sent to it.

I believe that the caption for the images on that page should read
something like "This is the way the original image would appear if 
displayed on various CRT monitors with gamma = XXX".

    Ethan


> 
> I am not certain, but I suspect the source of confusion is that CRT
> performance is also described using a gamma term, and this description
> is in some sense the inverse of what you do to the image.  I.e., a
> CRT with gamma = 2.0 looks dark.  To make the displayed image look
> "correct" you have to brighten it with a gamma correction of 2.0
> The Wikipedia article calls this an "inverse gamma correction",
> which may well be the correct jargon in some fields.  But that
> correction is what all programs I am familiar with apply as a
> "gamma correction".  Certainly it is what gnuplot has always done.
> 

Back to comp.graphics.apps.gnuplot | Previous | Next — Previous in thread | Find similar

Thread

Plotting into table with multiple columns Ingo Thies <ingo.thies@gmx.de> - 2011-08-27 11:24 +0200
  Re: Plotting into table with multiple columns Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2011-08-27 13:41 +0200
    Re: Plotting into table with multiple columns Ingo Thies <ingo.thies@gmx.de> - 2011-08-27 17:04 +0200
  Re: Plotting into table with multiple columns sfeam <sfeam@users.sourceforge.net> - 2011-08-27 22:56 -0700
    Re: Plotting into table with multiple columns Ingo Thies <ingo.thies@gmx.de> - 2011-08-28 12:59 +0200
      Re: Plotting into table with multiple columns Christoph Bersch <usenet@bersch.net> - 2011-09-02 10:23 +0200
      Re: Plotting into table with multiple columns "EAMerritt@gmail.com" <eamerritt@gmail.com> - 2011-09-21 16:43 -0700
        Re: Plotting into table with multiple columns Ingo Thies <ingo.thies@gmx.de> - 2011-10-08 13:16 +0200
        set palette cubehelix Ingo Thies <ingo.thies@gmx.de> - 2011-10-08 13:55 +0200
          Re: set palette cubehelix sfeam <sfeam@users.sourceforge.net> - 2011-10-08 10:48 -0700
            Re: set palette cubehelix sfeam <sfeam@users.sourceforge.net> - 2011-10-08 14:30 -0700

csiph-web