Densitometric vs Spectrophotometric measurements

[Kido]

Hello


I'm having an annoying issue regarding measurements.
We aim to print according ISO12647-2.

In the printery, wet sheets are densitometrically measured with a Techkon SpectroDens.

24 hours later, we measure these sheets with an X-Rite EyeOne, spectrophotometric.
The results are interpreted by GMG RapidCheck.

When comparing both results we notice following differences;
- 'Solid Ink Density'-result of EyeOne is less than SpectroDens
E.g. 1.30 < 1.50
- 'Tonal Value Increase'-result always differs between both methodologies.

These differences are still there when measuring a dry sheet with SpectroDens.


Does anyone have any idea of what a solution/workaround could be?


Thx in advance!

[gordo]

[SNIP]
In the printery, wet sheets are densitometrically measured with a Techkon SpectroDens.

24 hours later, we measure these sheets with an X-Rite EyeOne, spectrophotometric.
The results are interpreted by GMG RapidCheck.

When comparing both results we notice following differences;
- 'Solid Ink Density'-result of EyeOne is less than SpectroDens
E.g. 1.30 < 1.50
- 'Tonal Value Increase'-result always differs between both methodologies.

These differences are still there when measuring a dry sheet with SpectroDens.

Does anyone have any idea of what a solution/workaround could be?

Getting two instruments from the same brand to agree is difficult enough. (Some reasons are listed here: Quality In Print: Top reasons why color instruments don't agree

I would suggest that you choose one instrument as your "golden" standard unit then use a conversion chart, if needed, to align the other instruments to your golden standard. I.e. - "The man with two watches never really knows what time it is."

best, gordo

[Erik Nikkanen]

Hello


I'm having an annoying issue regarding measurements.
We aim to print according ISO12647-2.

In the printery, wet sheets are densitometrically measured with a Techkon SpectroDens.

24 hours later, we measure these sheets with an X-Rite EyeOne, spectrophotometric.
The results are interpreted by GMG RapidCheck.

When comparing both results we notice following differences;
- 'Solid Ink Density'-result of EyeOne is less than SpectroDens
E.g. 1.30 < 1.50
- 'Tonal Value Increase'-result always differs between both methodologies.

These differences are still there when measuring a dry sheet with SpectroDens.


Does anyone have any idea of what a solution/workaround could be?


Thx in advance!

Sounds normal. It is called dryback with respect to solids or something similar. The best explanation I have heard for it is that the difference is related to wet ink being more glossy than dried ink. Higher gloss on a solid will make it appear darker to an instrument due to the 45 degree geometry. the lower gloss reflects more light up into the instrument and makes the measured result lower.

Exactly how it affects the tone value, I am not sure since the tone is relative to the solid and screen under those different conditions.

I am sure you will get many more replies.

[Bret Hesler]

Could also be polarisation, which is switchable on the SpectroDens.

Bret

[Ozkan Hangisi]

Hello


I'm having an annoying issue regarding measurements.
We aim to print according ISO12647-2.

In the printery, wet sheets are densitometrically measured with a Techkon SpectroDens.

24 hours later, we measure these sheets with an X-Rite EyeOne, spectrophotometric.
The results are interpreted by GMG RapidCheck.

When comparing both results we notice following differences;
- 'Solid Ink Density'-result of EyeOne is less than SpectroDens
E.g. 1.30 < 1.50
- 'Tonal Value Increase'-result always differs between both methodologies.

These differences are still there when measuring a dry sheet with SpectroDens.


Does anyone have any idea of what a solution/workaround could be?


Thx in advance!

How about to check measuring set up? D50/Paper/Polarize for density and D50/Abs/Unpol/2* for color measurement. Also check which factor is in use for TVI calculation. Murray Davies or Yull Nielsen? Try Yull-Nielsen=1. I don't know whether there is a way to density calibration for EyeOne. But density match is not necessery to verify ISO and even density values are different, both device should measure dot gains very close.

Hope this helps

[mglouis]

Your pressroom could be measuring density with paper included and prepress with paper excluded. Paper often reads around around 0.05~.07
.
If a lightweight paper then the pressroom may use a black backing and prepress might use a white backing. This is a non-issue for most cover stocks.

Both should be set to Status-E or T or whatever your standard is.

My i1's and 530's and Intellitraxes all agree reasonably well - within 0.01 in terms of density.

Dryback is a concern as Erik mentioned. The higher the starting density the more the dryback and the more absorbent the paper the more the dryback. In our shop a wet density of 1.25 black on uncoated paper will dry back 0.10 in about three minutes. It continues to dry back at a slower rate until it reaches 1.05. On a gloss sheet under gloss aqueous coating a 1.70 will dry back to 1.65.

I do not see a significant shift in TVI between dry and wet sheets when using the same instrument. This is one thing I like about TVI process control over G7. There are a few methods for calculating TVI all of which can yield different readings. I am no expert but as far as I know there are XYZ, spectral, and "old fashioned" densitometric source readings and the calculations may be either Murray-Davies Equation, Yule/Neilson and perhaps there are others. Some software present actual values and others will display smoothed values so adjacent patches might skew the results of the patch you are measuring.

- Matt Louis

[mglouis]

The Techkon SpectroDens and i1pro are both spectrophotometers, by the way. The Techkon is designed to be able to "seem" like a densitometer. As far as I know nobody in graphic arts is making densitometers anymore.

Matt Louis

[Lukas Engqvist]

The solution to what. As mentioned above you will get differences on the two. As Gordo implies you decide which is your standard. If your i1 is what you measure then that is fine to use as a standard for Lab and Density. If the sheets were numbered and documented you will have a record of the wet density with the Techkon for the sheet that you used as reference, which means you can get measurability which in turn leads to repeatability.

It doesn't matter what the techkon value was when you did it right the thing is can you get the same value again. Since the sheets are wet when they come out, this value and repeatability of it is important for production. The dry values density and Lab are important for quality control, comparing to proofs, standards and comparing over time. If customers submit their own proofs it is more likely that they have used i1 than a spectrodens