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[filmscanners] RE: 8bits vs. 16bits/channel:cantheeyeseethedifference

> -----Original Message-----
> From: filmscanners_owner@halftone.co.uk
> [mailto:filmscanners_owner@halftone.co.uk] On Behalf Of Roy Harrington
> Sent: Monday, March 17, 2003 6:53 PM
> To: frankparis@comcast.net
> Subject: [filmscanners] Re: 8bits vs. 16bits/channel:
> cantheeyeseethedifference
> on 3/17/03 5:47 PM, Frank Paris at frankparis@comcast.net wrote:
> > This sounds like in going from 48 bit color to 24 bit color, you're
> > losing spatial resolution. I never realized that before.
> That's what
> > PS actually does? Of course that IS dithering, not
> aliasing. Dithering
> > is something engineering deliberately does. Aliasing is something
> > engineering tries to deliberately avoid.
> >
> Yes, PS really does do this.  It isn't too hard to
> demonstrate. (if you are curious enough I'd be glad show this).
> But don't worry about the resolution at all.  I'm only
> talking about differences less than the least significant bit
> -- very small by any measure.  No matter what PS did you'd
> lose data below the least significant bit.  The bad thing
> would have been to just truncate -- in that case the average
> value would actually drop by 1/2 LSB. If you have a value of
> 127.5 is HAS to go to either 127 or 128 so
> it makes sense to split the difference.   If the value was 127.3
> 30% would go to 128 and 70% would go to 127 -- much better
> than just truncating and even better than always rounding as well.

That is really cool if PS does this, but Franklin flatly denies it. He
says PS does a simple truncation, which would be pretty stupid if it
does, and I don't think PS is known for the stupidity of its algorithms.

However, I suppose Franklin is right in saying this dithering loses
tonal resolution, not spatial resolution. Sigh...I suppose he can't
always be wrong...

Frank Paris

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