QTR-Quadtone RIP

I think Shilesh has a valid point.  With the standard QTR transitions when
you use more inks the slope of the transitions are steeper since there are
more up and downs.  With just 3 grays the transitions are naturally wider.
Graph Piezo K7 curves and QTR UCk3 curves and note that the slopes a pretty
comparable.   What all this means is that you need to be more accurate
in the relative density measurements with K7 inks and QTR curves.
(I take it you are creating your own curves with K7 inks using QTR curves).

I must admit I haven't made many K7 curves since Cone provides them,
but like Shilesh says with K3 inks I've never had issue with smoothness.
What I think you are calling posterization is actually flat spots in a what
should be a smooth gradient.

In the new release I've included a bullseye.tif pattern in the Eye-One folder.
Print that out with your setup.  This shows anomalies very easily in the top
half.  Then the bottom half makes it easy to see where the issue is.
With a graph of the curves you can see which inks are in transition at that
point.  If its a flat spot the lighter ink is marked lighter that it really is.

Roy

On Mon, Mar 29, 2010 at 4:07 PM, Michael King <drmrking@...> wrote:
> Hi Shilesh,
>
>> I must say I have never ecountered posterization issues with customary inks
>> that use K, LK, and LLK alone, or as backbone followed by LM, LC, and others
>> for toning via use of "toner" or "copy curve from" in QTR ink setup.
>>
> Tomorrow I'll upload the section of the image that tends to posterise and
> you can try for yourself :)
> I'll email when its done. You might be surprised....
>
>>
>> I think Cone type overlap may (perhaps) be required when using 4+ gray
>> inks, which in my opinion is at best an overkill, and technical mas@#$%^tion
>> at worst. I have not seen a print that was better simply because it had 6 or
>> 7 shades of gray. Try to reduce the number of gray inks in your set up, and
>> use standard QTR curves design tools. I am curious what your eyes will see.
>>
> I don't think there's a particular reason why more overlap is required with
> more inks, but maybe as the ink curves bunch more together. I think its more
> about smoothing the tonal change in the inks sets, especially the splits.
>
> But the one place that overlap is required with some papers is at dmax. Some
> papers require both #1 and #2 ink densities to reach dmax, maybe 30 on the
> QTR graph scale for #2 ink, Canson Photorag is such a paper. With #1 ink
> only you achieve at best approx L= 1.0 less. On the other hand on other
> papers such as Epson Hot Press Bright, dmax can be achieved easiest without
> any #2 ink @ dmax.
>
> Mike
>
>
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