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Is it possible to zero-out LAB values

Is it possible to zero-out LAB values

2019-03-09 by skapuskar@...

When I used my old densitometer, I got better results with zeroed-out density values, that is, I measured my step wedges and zeroed-out to paper white.
Now I'm using a spectrophotometer and I obtain LAB values, like this:

93.9321
91.4298
88.1817
83.4927
78.2883
71.3222
65.4938
60.6404
54.9781
49.7342
44.4122
39.0966
34.6358
30.5362
26.4416
22.1175
19.0314
15.7048
12.0409
9.3780
7.6883

Is there any way to zero-out these values to convert the lightest value from 93.9321 to 100 and the darkest from 7.6883 to 0?

Thanks for any advice

Sidney


Re: Is it possible to zero-out LAB values

2019-03-09 by richard@...

What you are after is a basic normalization formula, but I don't think it will make a difference for the linearization. If you load your measurements into the A column in a spreadsheet, paste this into the B1 and drag down for the whole column.

=((A1-A$21)/($A$1-$A$21))*100

basically it is (value / minValue) / (maxValue - minValue) which will give you 1-0 and then multiply by 100 for 100-0


93.932110091.429897.09857488.181793.332390383.492787.895477778.288381.86095771.322273.783738765.493867.025687660.640461.398152754.978154.832695249.734248.752374144.412242.581495739.096636.418038234.635831.245724330.536226.492223226.441621.744519622.117516.730709919.031413.152365715.70489.2951609312.04095.046855549.3781.95921337.68830
Hope that helps,
Richard Boutwell

http://www.richardboutwell.com/

Re: Is it possible to zero-out LAB values

2019-03-09 by ozwille@sunflower.com

Hello Sidney,

Lab readings don’t work like density readings. You do not want to alter the Lab readings in the manner you mention, that would render the readings meaningless for linearization or any other purpose. There is no zeroing out to paper white with a spectrophotometer, you can only calibrate to the instrument’s calibration tile to ensure accuracy. The linearization software understands this and takes it into account.

What you do want to do is be consistent in your measurement technique. Always measure over the same neutral white backing, always calibrate before measuring, average multiple readings when possible, keep the spectrophotometer’s aperture and calibration tile free of lint and debris, use consistent movement with scanning spectrophotometers like an i1, etc.

The few times I’ve had unsatisfactory results using a spectrophotometer for linearization it’s always been because of a measurement error on my part or a problem with the print I measured.

Best Regards

Oz

Re: Is it possible to zero-out LAB values

2019-03-09 by skapuskar@...

Thank you Richard for the formula and Oz for your reply :-)

I have tried to zero the Lab values and as Richard mentioned, there is no visible difference.

Re: [QuadtoneRIP] Re: Is it possible to zero-out LAB values

2019-03-09 by Myron Gochnauer

I’m not even sure how to phrase this question (are these measurements logarithmic?), but:

Can these measurements be treated as arithmetically in the sense that if you just wanted to “zero out” (i.e. ignore) the (non-) whiteness of the paper, you could subtract (100-maxValue) from each reading?

With negative densities, it is/was common to subtract the (film) base + fog density from readings. So you might try to expose and develop for a Zone I density of “0.1 above base+fog”. If base+fog (i.e. unexposed but developed film) measured 0.2, then the target Zone I measurement would be 0.3.

Myron

On Mar 8, 2019, at 10:41 PM, richard@richardboutwell.com [QuadtoneRIP] <QuadtoneRIP@yahoogroups.com> wrote:

What you are after is a basic normalization formula, but I don't think it will make a difference for the linearization. If you load your measurements into the A column in a spreadsheet, paste this into the B1 and drag down for the whole column.


=((A1-A$21)/($A$1-$A$21))*100

basically it is (value / minValue) / (maxValue - minValue) which will give you 1-0 and then multiply by 100 for 100-0


93.9321 100 91.4298 97.098574 88.1817 93.3323903 83.4927 87.8954777 78.2883 81.860957 71.3222 73.7837387 65.4938 67.0256876 60.6404 61.3981527 54.9781 54.8326952 49.7342 48.7523741 44.4122 42.5814957 39.0966 36.4180382 34.6358 31.2457243 30.5362 26.4922232 26.4416 21.7445196 22.1175 16.7307099 19.0314 13.1523657 15.7048 9.29516093 12.0409 5.04685554 9.378 1.9592133 7.6883 0


Re: [QuadtoneRIP] Is it possible to zero-out LAB values

2019-03-09 by Simone Simoncini

maybe

scaled value=(original value - minimum value)*100/(max value - min value)
Show quoted textHide quoted text
On Sat, Mar 9, 2019 at 1:24 AM skapuskar@... [QuadtoneRIP] <QuadtoneRIP@yahoogroups.com> wrote:

When I used my old densitometer, I got better results with zeroed-out density values, that is, I measured my step wedges and zeroed-out to paper white.
Now I'm using a spectrophotometer and I obtain LAB values, like this:

93.9321
91.4298
88.1817
83.4927
78.2883
71.3222
65.4938
60.6404
54.9781
49.7342
44.4122
39.0966
34.6358
30.5362
26.4416
22.1175
19.0314
15.7048
12.0409
9.3780
7.6883

Is there any way to zero-out these values to convert the lightest value from 93.9321 to 100 and the darkest from 7.6883 to 0?

Thanks for any advice

Sidney


Re: [QuadtoneRIP] Is it possible to zero-out LAB values

2019-03-09 by Simone Simoncini

sorry, just replied without looking at previous entries.
Show quoted textHide quoted text
On Sat, Mar 9, 2019 at 1:24 AM skapuskar@... [QuadtoneRIP] <QuadtoneRIP@yahoogroups.com> wrote:

When I used my old densitometer, I got better results with zeroed-out density values, that is, I measured my step wedges and zeroed-out to paper white.
Now I'm using a spectrophotometer and I obtain LAB values, like this:

93.9321
91.4298
88.1817
83.4927
78.2883
71.3222
65.4938
60.6404
54.9781
49.7342
44.4122
39.0966
34.6358
30.5362
26.4416
22.1175
19.0314
15.7048
12.0409
9.3780
7.6883

Is there any way to zero-out these values to convert the lightest value from 93.9321 to 100 and the darkest from 7.6883 to 0?

Thanks for any advice

Sidney


Re: [QuadtoneRIP] Is it possible to zero-out LAB values

2019-03-09 by forums@walkerblackwell.com

That is the correct formula yes.

In excel (provided the top number starts at A1): =((A1-$A$21)*100)/($A$1-$A$21) then drag this down.

Best,
Walker




> On Mar 9, 2019, at 5:00 PM, Simone Simoncini ssimoncini@... [QuadtoneRIP] <QuadtoneRIP@yahoogroups.com> wrote:
> 
> 
> maybe
> 
> scaled value=(original value - minimum value)*100/(max value - min value)
> 
> On Sat, Mar 9, 2019 at 1:24 AM skapuskar@... <mailto:skapuskar@yahoo.com> [QuadtoneRIP] <QuadtoneRIP@yahoogroups.com <mailto:QuadtoneRIP@yahoogroups.com>> wrote:
> 
> When I used my old densitometer, I got better results with zeroed-out density values, that is, I measured my step wedges and zeroed-out to paper white.
> Now I'm using a spectrophotometer and I obtain LAB values, like this:
> 
> 93.9321
> 91.4298
> 88.1817
> 83.4927
> 78.2883
> 71.3222
> 65.4938
> 60.6404
> 54.9781
> 49.7342
> 44.4122
> 39.0966
> 34..6358
> 30.5362
> 26.4416
> 22.1175
> 19.0314
> 15.7048
> 12.0409
> 9.3780
> 7.6883
> 
> Is there any way to zero-out these values to convert the lightest value from 93.9321 to 100 and the darkest from 7.6883 to 0?
> 
> Thanks for any advice
> 
> Sidney
> 
> 
> 
> 
> 
> 



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