"Kenneth" <kdw### [at] gmailcom> wrote:

> That image has been part of POV-Ray for a long time-- probably created when the
> world still used CRT monitors(?)

That is indeed the case.

> But I'm wondering if a new 'kind' of image may
> be required, for setting up modern monitors.  In a nutshell, it seems that the
> 'proper' visual gamma of the chart *changes*, depending on the visual SIZE of
> the chart on the (discreet-pixel) monitor, vis a vis the monitor's chosen
> resolution (and/or the number of discrete pixels it has)--  specifically, the
> appearance of the black/white horizontal 'comparison' lines next to the gray
> swatches.  I could be wrong, but their appeance seems to depend on whether the
> lines actually 'line up' with the monitor's pixels...the result being an
> apparent change in what should be the 'proper' gamma.

That's a perfectly correct observation: Setting your operating system's display
resolution to something other than the monitor's /native resolution/ will cause
the monitor to perform interpolation, which means averaging pixel values.
Depending on how this is implemented, it will rarely be a linear interpolation
of physical brightness.

(The striped patter in itself is a means to force linear interpolation of
physical brightess: Squinting your eyes a bit, your vision is blurred, blending
the black and white stripes to a uniform patch of grey with the same total
brightness.)

While this fact is indeed not mentioned in the reference section, the tutorial
section on gamma handling (?.3.4) does sport a note to this effect.


> As an experiment, I downloaded the gamma chart image and brought it up in
> several of my image apps. There, it's an easy matter to reduce the screen size
> of the chart... not by actively reducing its pixel count, but by simply using
> the app's 'magnifier' tool. A *smaller* appearance of the chart changes what WAS
> a proper 2.2 gamma appearance to a gamma of 1.0! Of course, the app itself (or
> the monitor or computer?) must be using some kind of internal 'blending' to do
> this, which may be the reason--so I could be wrong about my method. But it's
> something I noticed-- in a less extreme way-- when using just the POV-Ray help
> file and  its chart, when I changed the monitor's resolution.

In this experiment, the interpolation is indeed performed before the image even
reaches the monitor, namely by the image displaying software; and indeed this is
also rarely done linearly with respect to physical brightness, and thus also
messes with the original intention of the image.

This issue is also explicitly taken into account by the tutorial section on
gamma handling.


> All in all, this is technical mystery to me. Comments are welcome; I'd LIKE to
> be proven wrong ;-)

No, you're perfectly right in your observations.

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