QTR-Quadtone RIP

When figuring the relative densities do you figure them all relative
to K or to the next darkest gray?  I'm using UT7 ink with a 2200 on a
PC and have made cool and warm curves measuring all the ink densities
against K  but I read here, I think, that it might be wrong.  I've
reread Tom Moore's excellent user guide but am not clear.  The prints
I'm making now are the best I've done so it measuring against K can't
be too far off.

Thanks,

Tom

--- In QuadtoneRIP@yahoogroups.com, "Tom Husband" <thusband@s...> wrote:
>
> When figuring the relative densities do you figure them all relative
> to K or to the next darkest gray?  I'm using UT7 ink with a 2200 on a
> PC and have made cool and warm curves measuring all the ink densities
> against K  but I read here, I think, that it might be wrong.  I've
> reread Tom Moore's excellent user guide but am not clear.  The prints
> I'm making now are the best I've done so it measuring against K can't
> be too far off.

It's got to be right, because you need a common baseline to place all
the inks. The density relative to the darkest color is an acceptable
baseline (although I prefer placing them according to measured
density). Density relative to the preceeding color isn't a baseline.

--- In QuadtoneRIP@yahoogroups.com, "Tom Husband" <thusband@s...> wrote:
>
> When figuring the relative densities do you figure them all relative
> to K or to the next darkest gray?  I'm using UT7 ink with a 2200 on a
> PC and have made cool and warm curves measuring all the ink densities
> against K  but I read here, I think, that it might be wrong.  I've
> reread Tom Moore's excellent user guide but am not clear.  The prints
> I'm making now are the best I've done so it measuring against K can't
> be too far off.

It's got to be right, because you need a common baseline to place all
the inks. The density relative to the darkest color is an acceptable
baseline (although I prefer placing them according to measured
density). Density relative to the preceeding color isn't a baseline.

--- In QuadtoneRIP@yahoogroups.com, "Tom Husband" <thusband@s...> wrote:
>
> When figuring the relative densities do you figure them all relative
> to K or to the next darkest gray?  I'm using UT7 ink with a 2200 on a
> PC and have made cool and warm curves measuring all the ink densities
> against K  but I read here, I think, that it might be wrong.  I've
> reread Tom Moore's excellent user guide but am not clear.  The prints
> I'm making now are the best I've done so it measuring against K can't
> be too far off.
> 
> Thanks,
> 
> Tom
>

Hi Tom,

What I do is measure each gray against the next darker gray.  There are two
reasons for this: 
1)  that's the transition that will happen on the print 
2)  measurements are more accurate.  a 5% gray is a lot easier to measure
against a 10% gray rather than the 100% black.

However the numbers entered are always relative to black.  So you multiply
the new factor by the factor of the darker gray.  For example:  measure a
dark gray to black and get 30%.   Then measure a light gray against the dark gray
and get 40%.   So the final values are K=100,  DarkGray=30 and LightGray=12
since 40% * 30% = 12%

In practice its probably not a big deal for just 2 grays.  When you get to 7 grays
I think it would be really hard to measure.  The linearization later on tends to
fix up the transition too.

Roy