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Help with a "bit of simple math".

2015-10-14 by f_56_f@...

This is from Tom Moore's QTR user manual:

I'm apparently math impaired because for the life of me I can't figure out a formula that will give me the answer of 43.2%Black. I can come close (43%) by trial and error but I think a formula would be better and in my case more accurate.

So, I guess my question is: can any one provide the formula for determining that 43.2% result.

Thanks

RE: [QuadtoneRIP] Help with a "bit of simple math".

2015-10-14 by m venz

Hi

there is a spreadsheet somewhere that does this calculation (in one of the groups or inkjetmall or somewhere)

However, it goes like this.

The answer you want is 1.29

the question is: what % of the pure black ink gives a density of 1.29

you find the answer is somewhere between 40% (density 1.22) and 45% (density 1.33).

without any maths you can see that 1.29 is not too far away from halfway between these. Halfway would be at 42.5% with a density of (1.22+1.33)/2 ie 2.55/2 = 1.275 so the exact answer will be a wee bit more.
;
Using the maths:
from 40% to 45% represents a 5% change
while the density grows from 1.22 to 1.33: a change of .11
So: THIS IS THE MATHS, .11/5 = .022
Which means each 1% extra ink gives .022 extra density.

So if you start at 40% ink with 1.22 density add .022 repeatedly until you arrive at 1.29

ie 1.22+n x .022 = 1.29
subtracting 1.22 gives n x .022 = .07

solve and you get a touch more than 3 lots of adding;

Final answer: 40% + 3 lots of adding = 43%

Hope you can follow the explanation

From: QuadtoneRIP@yahoogroups.com
To: QuadtoneRIP@yahoogroups.com
Date: Tue, 13 Oct 2015 19:59:22 -0700
Subject: [QuadtoneRIP] Help with a "bit of simple math".

This is from Tom Moore's QTR user manual:

With a densitometer:
1. measure the 100% Light Black patch: Density 1.29
2. measure the 40% Black patch: Density 1.22. I selected 40% by eye,
but you can use the densitometer to find the darkest patch with
density less than the density of 100% Light Black
3. Measure the density of the next darker patch – 45% Black: Density
1.33.
Then it’s bit of simple math to calculate the percentage of black needed to
produce the same density as 100% Light Black. In this case we get a value
of 43.2% Black is equivalent to 100% Light Black.

I'm apparently math impaired because for the life of me I can't figure out a formula that will give me the answer of 43.2%Black. I can come close (43%) by trial and error but I think a formula would be better and in my case more accurate.

So, I guess my question is: can any one provide the formula for determining that 43.2% result.
Thanks

Re: Help with a "bit of simple math".

2015-10-14 by richard@...

This is the interpolation formula I use. I remember this formula (or one similar) being described in one of the QTR Workflow write-ups but I don't recall exactly where off the top of my head.

(((Target density - Next Lower Density) / (Next Higher Density - Next Lower Density)) * (Patch# for next lower density + 5)) * cross over % of the next darker shade

That last bit of the "cross over percentage of the next darker shade" is what actually give you the value you put in think descriptor file. This first cross over point is easy because it is just 100. The next cross over point is also easy because the relative density of that shade is multiplied by 100% (the cross over point of the next darker shade). The cross over point of the next lighter shade is where it can be confusing because you need to multiply the relative density for that shade by the cross over point (as a percentage) of the next darker ink.

Hope that helps,

Richard Boutwell

Re: [QuadtoneRIP] Help with a "bit of simple math".

2015-10-14 by Myron Gochnauer

It would probably be helpful to many, if not all, of us if someone who is really on top of this could/would create and share a labeled diagram along with the formula using these labels, and a simple, general explanation of what you are supposed to be doing/accomplishing.

I know that when I last used the process - - more than a year ago - - it wasn’t very difficult once I realized what was needed. But that understanding has faded with time, and as I read most of the current thread I couldn’t quite get a grip on it again.

Having taught law for more than thirty years, I know that not everyone “gets it” the same way. If there are four ways of approaching an idea, you’d better use all four, and hope that by the time you’re finished the lights have gone on in all of the eyes in your classroom. (Wishful thinking, probably!) Some people need only an appreciation of the general principle and the point of it, while others need a step-by-step recipe, and still others need a strongly intuitive exemplar of the principle along with sample to experiment with. . . And everyone needs practice!

Myron

On Oct 14, 2015, at 2:34 AM, richard@richardboutwell.com [QuadtoneRIP] <QuadtoneRIP@yahoogroups.com> wrote:

This is the interpolation formula I use. I remember this formula (or one similar) being described in one of the QTR Workflow write-ups but I don't recall exactly where off the top of my head.

(((Target density - Next Lower Density) / (Next Higher Density - Next Lower Density)) * (Patch# for next lower density + 5)) * cross over % of the next darker shade

That last bit of the "cross over percentage of the next darker shade" is what actually give you the value you put in think descriptor file. This first cross over point is easy because it is just 100. The next cross over point is also easy because the relative density of that shade is multiplied by 100% (the cross over point of the next darker shade). The cross over point of the next lighter shade is where it can be confusing because you need to multiply the relative density for that shade by the cross over point (as a percentage) of the next darker ink.

Hope that helps,

Richard Boutwell

Re: [QuadtoneRIP] Help with a "bit of simple math".

2015-10-17 by paulmwhiting@...

A while back I uploaded a pdf to the Files/Tools library, which explains how to use a 20 step grey scale, flat bed scanner and a spreadsheet to create that forumula. The problem I had with the interpolation method is that it is a linear approach whereas the pdf (called QTR Curve Making) file lets you plot the curve and then generate a curve and logarithmic formula in a spreadsheet. You don't have to know what a logarithm is.

I won't try and explain it further here, but simply suggest taking a look at the pdf. It may look confusing at first read (it certainly was confusing for me!) but after a while it began to sink in.

In fact it's time for me to dust off this method when I break open a bottle of the new Eboni black, I understand it is slightly warmer than the previous version. This will require a new curve for the papers I use.

Hope this helps,

Paul

Re: [QuadtoneRIP] Help with a "bit of simple math".

2015-10-17 by richard@...

Paul, if I remember correctly, your PDF works with the printed 21 step target for making a correction curve, and usd after printing with the initial partitioned profile (after setting the cross over points).

This interpolation method I posted is for finding the cross over points, and is based on measurements of the ink separation page, printed after setting the ink limits. 

I will go back to your pdf and see if it can be used for finding the cross over points. 

Richard Boutwell

Re: Help with a "bit of simple math".

2015-10-18 by paulmwhiting@...

Richard,

Thank you for your comments... I see now we're talking about two different procedures. But I'm embarrassed to say I can't remember what is meant by cross over points! I'm in over my head...

Regards,

Paul

QTR-Quadtone RIP

Help with a "bit of simple math".

Help with a "bit of simple math".

RE: [QuadtoneRIP] Help with a "bit of simple math".

Re: Help with a "bit of simple math".

Re: [QuadtoneRIP] Help with a "bit of simple math".

Re: [QuadtoneRIP] Help with a "bit of simple math".

Re: [QuadtoneRIP] Help with a "bit of simple math".

Re: Help with a "bit of simple math".

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