Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, Steve Kale <stevekale@b...> 
wrote:
>
> Re your mention of 25 points.  I assume the "For Input Values Of:" depiction
> we see in Colorsync Utility which has a range of 0-24 is linked to this.  I
> have never fully understood how to read this.
>

The format isn't limited to 25 points.  That's just what the profile maker
decided was a good compromise because of profile size.  I think the spec
says 2 to 4096 points.  But consider 256 points:  on a 3 color profile that
256 * 256 * 256 points = 16 million pts.  Each point is 3 values * 2 bytes.
Then times 3 intents in each direction.   That would be upwards of 600 megabytes
for a profile.  Clearly not practical.  Even 25 points makes a big profle -- .5 MB.
With my gray profiles using just the OutCurves, I calculate and store all 256
values but the total size is just a couple K bytes.  With the In/Out curves
you get a lot more precision for a lot less space.

What you are looking at in ColorSync Utility is one slice of the 3D clut.  You
fix 2 of the dimension values and it shows the graph of the other dimension.
The numbers are all normalized 0 to 1, so when you see 0-24, 24 represents 1.
All the others are fractions.  The LUT is very much like PS Curves with evenly
spaced points.  You just have to imagine that in 3 dimensions.  The In and Out
curves are easier to understand since they are 1 dimensional.

There is a OS X program that shows the innards of the icc file but requires using
the command line interface.  Let me know if you want to pursue that.

Roy