QTR-Quadtone RIP

Phil,

If you are talking about the response curve that an individual ink has, it will not have bunps in the curve (or should not), because inks generally are not going to have a discontinuous response curve on the paper.  They may shoulder off or otherwise not be linear or in an ever-increasing slope curve, but it is unlikely for inks to show a real discontinuity.

So when you make a profile using straight inks (without supplying a specific ink curve of your own), the inks are not going to produce a real erratic behaviour in general, unless something went wrong along the way.

When you take density readings the range of readings may go from about .15 or so for the paper (higher with non-optically brightened paper) up to around 1.8 or so (up to 2.4 or so for the best gloss papers).  That doesn't give a lot of range for the readings to fall if you take the readings out to 1/100 units of density.

Because of this, the readings can have considerable problems with the error resulting in a greater difference than the actual density difference between readings is supposed to be.

When I put the readings into Excel, it is to identify the likely locations of these error readings and nudget the likely high readins down, and up for the likely low readings to ensure that the program does not see a high then low error reading pair as a flat spot which violates the 'constantly increasing' requirement.

Normally, I adjust the readings by no more than 1/2 of the minimum step of the densitometer (1/100) to avoid these problems.  That is consistant with what the max. error should be for the densitometer.

That's a long way of saying that I smooth the curve a little, and it makes the process go more smoothly.

All bets are off if you are using a custom curve for any of the inks that hasn't been very carefully done, though.

---Michael


--- In QuadtoneRIP@yahoogroups.com, "grimmieoldfart" <grimmieoldfart@...> wrote:
>
> Michael,
> 
> when you say "smoothed" out the bumps, what exactly do you mean? I have been working on Canson BFK Rives and on the warm inks, it will curve to about 50% and the 55% will dip but return to normal at 60%, Ex., 50% Lab B = 3, 55% Lab = 2.5, 60% Lab B = 3. Even though the Lab L curve is smooth with no real flat spots, it seems the Lab B curve has influence over the linearization process as well.
> 
> Phil
>