[filmscanners] RE: 8bits vs. 16bits/channel: can the eye seethe difference

["Paul D. DeRocco" <pderocco@ix.netcom.com>]

> From: Austin Franklin
>
> What about any other display program (not PS), or printing?  I mean, the 8
> bit data is simply 8 bit data, the "in between" data just doesn't exist.
> Creating this "in between" data has to be something that is deliberately
> done, and it may in fact be creating something that didn't exist in the
> first place!

If you have an area of blue sky whose actual analog color levels are, say,
R=85, G=110 and B=182.75, and there is one LSB peak-to-peak noise in the CCD
used to capture the levels, then about one quarter of the pixels will have
blue values that round down to 182, and about three quarters will round up
to 183. When this is displayed, the eye or brain will average them,
producing the same effect as an actual value of 182.75.

Indeed, this is how most A/D and D/A converters now work. Your CD player,
unless it's quite old, probably has a 1-bit D/A converter, running at many
megahertz, instead of a 16-bit D/A converter running at 44.1KHz. It's also
the principle behind inkjet printers, which are basically on/off devices.

> I did not know PS did this, thanks for the info.  Do you have a pointer to
> where it is documented?

I haven't searched the help file, but the gradient tool has a Dither check
box, as does the Color Settings dialog in the profile conversion section.

--

Ciao,               Paul D. DeRocco
Paul                mailto:pderocco@ix.netcom.com


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