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

["Austin Franklin" <austin@darkroom.com>]

Hi Paul,

> > 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.

I agree with that, but that's not really dithering.  That's merely a
property of averaging, and how your eye works.  Dithering is deliberately
adding random noise to a signal.  What you are describing is called
aliasing.  They are entirely different.

> 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.

I don't believe that is true.  That is only used in the lower and some
intermediate level CD players.  It's called delta-sigma conversion, and I
was one of the original developers of this technique.  The high end units I
am aware of still use very high end 20 bit A/D converters.  But, that's not
got anything to do with dithering either ;-)  See my other post for a
Digital Signal Processing definition of "dither".

Regards,

Austin

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