[argyllcms] Re: Profiling flexo presses

Roberto,

Those are all good and puzzling observations?

If indeed I choose a grid resolution of 33 for Lab to CMYK, which is the
maximum with most profiling software, don't I get 100/(33-1) = 3.125% steps,
at best?  

> I've just realized that 2% in the profiling targets is basically
> useless... because it won't be able to make a difference in the
> profile itself, due to the grid.
> To start with, in typical "non-link" profile usage for separation, the
> PCS->device table is used ; that table wastes 70% or so of the space
> in colors that are either nonexistent or out of gamut.

You wonder why couldn't there be some scaling factor that allows making
intelligent use of the encoding space.

> If the table
> were for example 33 gridpoints in each direction, it's likely that the
> "in gamut" colors would extend over less than 15 gridpoints in
> average. That would give you about 100/14= 7% steps *if* the device
> correlated linearly with PCS space, which of course it doesn't. So
> it's more likely to say that you won't have a PCS gridpoint that
> renders less than 8-10% in at least one of the device channels.

Most CMYK profiles I seen only have 17x17x17 CLUT in the Device -> PCS
direction. I was once told that increasing the grid resolution would create
monster profiles?

> Being that the target has patches with 10% values (and some even 5%),

ECI2002 target has patches with 2% values. I'm not following?

> the influence of readings from 2% patches will be almost -if not
> totally- null.

Hmmh? Building flexo profiles with ProfileMakerPro actually yields accurate
Device -> PCS mappping, matching the original target measurements. Could it
be that the "influence of readings from 2% patches" you refer to is not
quite as you think?

> Now, if the profile were to be used for proofing (device->PCS) or with
> a CMM that does on the fly table reversal (instead of using
> pcs->device it just reverses device->PCS) such as argyll, then it's
> better. 

Could you please explain that point further?

> But still, to have the 2% patches work in profiling, you'd
> need to build a profile with 41 gridpoints (which would give you 2.5%
> resolution on device channels), which most profiling packages don't
> (argyll does, right?).

Please excuse my ignorance, but you mean I could create such profiles with
argyll? 41 grid points both ways?

> Furthermore, you just can't print 2% on a flexo press that has not
> been linearized, at least in the highlights by means of a bump curve.

What do you mean roberto? All the flexo printers I know of routinely print
2% dots. Without the need of bump curves.
 
Regards,

Roger Breton  |  Laval, Canada  |  graxx@xxxxxxxxxxxx
http://pages.infinit.net/graxx

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