Re: [APML] CRT vs Flat Panel for display of astrophotos

["Rick Kellogg" <rkellog1@twcny.rr.com>]

Dave Hutchison wrote:

> Contrast ratio is measured as follows:
>
> Luminance at peak white over Luminance at black.
> It does not account for number of bits used to
> represent peak in/out. The reason why you
> can get so many values for this is because
> there are different conditions under which the
> measurement is taken.

Then (IMHO) this a pretty meaningless measurement.
For a CRT, under no ambient light, in a black room that absorbs all light
from the CRT, I would expect to get very high contrast ratios by just
turning down the brightness until black areas emit no light (other than what
is scattered internally).  But that does not mean that all CRTs with similar
brightest white to black ratios can display a good gray scale.

I did not mean to imply that bits have much to do with it (yet I knew that
is how it would be taken).  An analog display driven by a voltage, does not
have any bits, but has an equivalent signal/noise level that limits the
dynamic range possible.  Neither bits nor S/N should be the limiting factor,
yet 8 bits does not seem to be enough on high end broadcast video recorders
to eliminate the perception of banding on gradients of small color range.
But this is probably a red herring on my part anyway, and not worth any
further thought.  Of the 10 bits, it is likely only 7 1/2 - 9  are signal.
A lot of these gradient issues are from computer created images, not signals
from cameras, and thus have artificialy high dynamic range, that can band
when limited to 8 bits.


Rick Kellogg

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