[filmscanners] RE: Dynamic range

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

Roy,

> My 8-bit versus 16-bit comment was in a very different context.  I was
> talking about a 16-bit Photoshop that was ready to be printed.  Thus
> value 0 was the max black and value 65535 was the max white.   At this
> time the file was converted to 8-bit such that value 0 represents the
> same max black as 0 in the 16-bit file, and value 255 in 8-bit file
> represents the same max white as 65535 in the 16-bit file.  So both
> files represent the same black to white range.

Correct, and that is DENSITY range ONLY...NOT DYNAMIC range.

> In this context I
> say the 8-bit file and the 16-bit file have the same dynamic range
> because they represent the same tonal range on a output print.

That's your misunderstanding.  If you use the dynamic range equation, any
one you want, and plug in the numbers...you'll see that what you believe is
wrong.  When you quantify MDS, you quantify it relative to all the other
values.  The 0 value in the 8 bit file now represent ALL the values from
0-255 in the 16 bit file...they are now "combined" into one value.
Remember, each value represents an actual RANGE of values from the image,
and it's that range that "a" value represents that is the MDS...and
converting 16 bit to 8 bit you've now increased the range of values by 256
times, therefore increasing MDS.

> The
> endpoints are the same only real difference is how many levels are in
> between.

Correct, and that is why dynamic range and density range are NOT THE SAME.

Austin

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