RE: filmscanners: Re: Hello, thanks, and more.

["Austin Franklin" <darkroom@ix.netcom.com>]

> 1) Bits.  I need some clarification on what the siginificance of all
> the different bit-rates are about for color.

You don't mean "rates".  Rate is a measure of speed (or periodicity)...and
doesn't apply here.

> For example,  one person
> mentioned that there is no real advantage in 16-bit over 8-bit color
> for printing.  Someone else mnetioned "editing in 16-bit."   The Canon
> software only offers scanning in 24-bit color,

24 bit color is a quantity of 3, 8 bit colors (8 bits for red, 8 bits for
green and 8 bits for blue)...so that's considered 8 bit mode.  You are
confusing pixel depth with overall color depth.  36 bit color is three 12
bit pixels (12 for red, 12 for green and 12 for blue).

> 2) Sizing.  Now this is just specifying the pixel dimension of the
> image, correct? Without changing the resolution.

A bit of background...  Resolution really only has meaning when you are
scanning, or outputting (as in printing or seeing the image on the screen),
but nothing to do with the physical image in memory...since it is just an X
by Y number of pixels, with no unit of measure associated with it.  It's
only when you output it that you give it a number of pixels per unit of
measurement...so...when you resize an image, what you are doing is assigning
the number of pixels per unit measurement (usually per inch), and that
changes the resolution...unless you interpolate/decimate the data...which
means to add or remove pixels.  What this does is allow you to keep the same
output resolution and get a larger or smaller image.  Sorry if that confuses
you, but in an email, it's hard to describe...

> For example, I scan a slide at
> 2720 dpi, and I get a 28.9 MB TIFF file that measures something like
> 3889x2550 pixels.  After adjusting color and brightness, etc, and
> saving,  I go into the properties dialogue and specify a web-based
> size, i.e. about 750 pixels in the longest dimension. Is that
> "downsampling?"

Yes.

> Is that process in itself "lossy?"

Yes, very much so.  Think about it.  You are converting an image that WAS
3889 pixels across, now to 750 pixels across.  That's called "decimation",
technically.  What it is doing is throwing out (or averaging...or some other
more advanced algorithm) every 4 out of 5 pixels.  That's a LOT of loss.

> In any case, as a result of reading your advice I am now:
>
> Always scanning at max res, ie 2720 dpi.

If that is the optical resolution of your scanner, that is correct.