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

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

>Contrast ratio of 600 etc. <
(I'm about to say something controversial, please keep responses civil)

I too have no idea exactly how contrast ratio is measured or what it means.
But what I took it to mean, is the ratio of the brightest (non-saturating)
picture value to the smallest discernable difference in picture value (on a
linear scale).  This is the same definition that most use for dynamic range.

Now a say your display is set for a gamma of 2.2 (sRGB) with 8 bits/pixel,
then the light from the brightest pixel value can be represented by:

gain*255^2.2 + bias + ambient light reflected off display.

The dimmest pixel by:

gain*1^2.2 + bias + ambient light reflected off display.

If the bias and ambient light are small compared gain*1, then the dynamic
range (or contrast ratio) is:

255^2.2 =  ~200k.

Now all this does is say how much dynamic range is in the number system,
using 8 bits/pixel, gamma 2.2.  It says nothing about how much dynamic range
is in your display.   It also ignores that there are 3, 8 bit numbers/pixel
(one for each color).

But I would point out that high end broadcast digital VTRs use 10
bits/pixel, not 8, so as not to see banding in subtle color shades. So while
I don't know how good CRTs actually are, I would bet they are greater than
600:1.


Rick Kellogg

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