When to use ∆E2000 vs ∆Eab

[Vernon Roberts]

My understanding is ∆E*ab for offset process work, measuring primaries and overprints and ∆E2000 for press to proof, PMS, and digital print evaluation.

I use Heidelberg's color management suite, so I reached out to them to ask their opinion. They said what I said above. Maybe because their suite lends itself to that workflow.

We just bought a new Techkon Specto Dens, and I've been learning how the GrayGuide works on it. It defaulted to ∆E2000 for primaries, but if you measure an R,G, or B patch it will display ∆Eab. I was trying to understand why.

What is your opinion on this? What are you doing in your shop? and why do you think this way?

 

[arossetti]

DeltaE76 = a direct line between target and measured. So if it is 5 points away you have a DeltaE of 5.
DeltaE00 = an interpretation of how the human visual system would view the difference. So if we are less prone to being able to identify lightness differences the colors may be 5 points away but since it is just a L* difference the formula weighs that differently and it is a DeltaE of 3.

 

[Vernon Roberts]

I understand this. My question is still:
What is your opinion on this? What are you doing in your shop? and why do you think this way?

 

[arossetti]

I'm in an all digital environment currently, I use deltaE00.

However on press using 76 makes sense to me because you are wanting to measure the actual change of the printer in CMYK RGB. The lightness of your yellow could change but it might not register if you are using 2000. But this also goes to how useful is it for the pressman to measure spectral versus densities. If his cyan B* value begins to change what can he do about it?

 

[gordo]

I'm in an all digital environment currently, I use deltaE00.

However on press using 76 makes sense to me because you are wanting to measure the actual change of the printer in CMYK RGB. The lightness of your yellow could change but it might not register if you are using 2000. But this also goes to how useful is it for the pressman to measure spectral versus densities. If his cyan B* value begins to change what can he do about it?

Worthy of a separate thread.

My 2 cents worth.

This is IMHO, a basic disconnect between the standards groups and the pressroom.
A press is not designed to print color. Color results from the interaction betwenn ink, substrate, lighting, and observer.
A press, instead, is designed to lay a film of ink emulsified with fountain solution onto the substrate. In the case of offset, that film of ink needs to be about 1.25-1.75 microns thick otherwise the process fails. So, all of the press operators attention is focussed on the controls available - SIDs because that’s an indirect measure of ink film thickness, water/fountain solution, impression pressure, and speed rather the things over which he has no control, e.g. ink hue, substrate, lighting, and viewer.

 

[Vernon Roberts]

In my opinion, the pressman should use both, and understand how one effects the other. The pressman, to an extent, does have control over the solid LABs, via density moves. As long as the LAB aims established for the ink+stock combination are within the printable SIDs.




The process standard should include, stock, ink, and lighting standards. But you’re right, it’s not a discussion on whether or not to use density vs LAB in the press room.




arossetti

The LAB moves are mostly 1 dimensional moves. More density in Cyan should make B* and L* lower. Shaping the gamut to your reference.




It would be interesting to hear from someone using LAB in the press room, at the press, in production, in combination with SIDs.

 

[arossetti]

arossetti

The LAB moves are mostly 1 dimensional moves. More density in Cyan should make B* and L* lower. Shaping the gamut to your reference.

Not if the B* and L* moves but just B*. Say if the B* goes from -50 to -45.

 

[Vernon Roberts]

You’re right, there is only so much control they have, but they have some. It’s all GRACoL in my shop and it’s very achievable. If they can’t do anything about hitting the standard, maybe it’s an unrealistic standard. In my experience, the LABs move in one pretty consistent, predictable way in relation to density.

 

[Deleted member 16349]

Not if the B* and L* moves but just B*. Say if the B* goes from -50 to -45.

As Gordon has stated, the resulting colour is an outcome of how the press is printing. In general, one should use a physical variable as a control target not an imaginary value. Colour does not exist in Nature and is just a calculation based on reflectance multiplied by functions. That is why density is the proper control variable, since as Gordon states, it is very closely related to the amount of ink in the printed ink film of the solid. For offset, the consistency of the solids are very closely related to the consistency of the dot gains.

Trying to control a press with Lab values is problematic. The colour scientists suggest using Lab values but they don't explain how the control method should be done. On press, moving through a path of density values for a solid that never actually hits the target Lab values is absurd as a control concept. And when thinking of the Lab value for a screen, then it becomes even more complicated to make a move. One normally would need moves in all three CMY values to move from one colour value to another. Two up and one down or the other way, two down and one up.

Colour has nothing to do with the printing process. The printing process is a matter of placing the right amount of pigment in the right locations on the substrate. Colour is just the out come of this and if the process is consistent and predictable, then one can predict the colour output if one has control of the real physical variables.

 

[Vernon Roberts]

You know, I don’t even know a response to this. I really don’t want to try and teach on this forum. Obviously you guys have no experience with my original question.

To continue this debate, modern software and devices easily make these moves for the pressman. There is nothing complicated about it. You should understand and use both, LAB can reveal problems that density can’t. Density can’t reveal if the unit is contaminated. The same density every time doesn’t equal the same LAB. You can’t just measure density blindly and wonder why you can’t match proofing anymore.

Please don’t reply to this post if you have no experience on the original topic. I’ve heard all of this before. You’re not telling me anything I haven’t heard already.

 

[arossetti]

You know, I don’t even know a response to this. I really don’t want to try and teach on this forum. Obviously you guys have no experience with my original question.

To continue this debate, modern software and devices easily make these moves for the pressman. There is nothing complicated about it. You should understand and use both, LAB can reveal problems that density can’t. Density can’t reveal if the unit is contaminated. The same density every time doesn’t equal the same LAB. You can’t just measure density blindly and wonder why you can’t match proofing anymore.

Please don’t reply to this post if you have no experience on the original topic. I’ve heard all of this before. You’re not telling me anything I haven’t heard already.

Haha, I respect the opinions of Gordo and Professor Nikkanen above most on this forum. I wouldn't be so dismissive. What is your companies SOP for when cyan goes from -50 to -45 when LA stay the same?

 

[Deleted member 16349]

Density can’t reveal if the unit is contaminated. The same density every time doesn’t equal the same LAB. You can’t just measure density blindly and wonder why you can’t match proofing anymore.

.

I agree with you. I think there might be two issues here. One is process control and the other it trouble shooting. Density is good for process control but as you say, it does not help with a problem such as contamination. One can not correct contamination on press, while it is running with Lab values either but for sure it tells you some thing has gone wrong. For sure, Lab helps with trouble shooting when something has changed.

I hope you get the answer you need from others on the forum.

 

[Vernon Roberts]

Haha, I respect the opinions of Gordo and Professor Nikkanen above most on this forum. I wouldn't be so dismissive. What is your companies SOP for when cyan goes from -50 to -45 when LA stay the same?

I told you wrong earlier on the cyan move. I was responding during intermission at a hockey game, so that's my excuse. Here is a document that helped me see how LAB moves. It was provided to move from Heidelberg as a scan a long time ago, but I have cleaned it up, so it may help someone else. I have verified this to be correct. I scan P2P targets weekly. If you were to track it in an a*b* view, you could draw out a path. Maybe look something like this.

Not sure exactly how much a* moves, but not much. Mostly cyan moves up and down in L* and b*, like the document says.

If you're all digital, as in xerography, this doesn't apply, and I wouldn't be so concerned with primaries and only something like an "All patches mean" test using ∆E2000.

Our shop prints all kinds of things that run digital one week and offset the next, based on quantity. I have hybrid jobs where the cover runs digital and the text runs offset. I've had crossovers that are half and half. Your digital side should be simulating a standard that your offset side is printing to. Clients don't care how it's printed, they just know that this week the same color they sent in printed differently than last weeks did.

 

[Puch]

What we've experienced in practical use is that dE2000 is too forgiving. There might be color differences dE2000 presents to be much lower than they are in the real life, especially in the skintone region. Therefore we still use dE76 for every measurement and certification.

 

[Vernon Roberts]

What we've experienced in practical use is that dE2000 is too forgiving. There might be color differences dE2000 presents to be much lower than they are in the real life, especially in the skintone region. Therefore we still use dE76 for every measurement and certification.

Thanks so much for the feedback. Is this for digital and offset?

 

[cementary]

We're pure offset printer. We use dE76 for solids and overprint to confirm we're in standard. Also we use dE76 for proofs because we use same for print. However we use dE00 with pms colors because our supplier use his own set of pigments with Inkformulation and formulate ink to comply it with pantone book but on production substrate. We've found that dE00 is better for light colors along with M1 condition

 

[arossetti]

I don't think you are understanding my question. Your position is that with spectral measurements you can identify when color shifts, not just density changes. My point is what does that information do for the pressman when he is 30m sheets into a run at 15000sph? If they see the cyan shift in B* only, what does your SOP describe to fix the problem? If this information is important to you what are you doing with that information?

 

[Vernon Roberts]

I don't think you are understanding my question. Your position is that with spectral measurements you can identify when color shifts, not just density changes. My point is what does that information do for the pressman when he is 30m sheets into a run at 15000sph? If they see the cyan shift in B* only, what does your SOP describe to fix the problem? If this information is important to you what are you doing with that information?

A process standard based on spectral data is setup on a scanning device that scans the color bar or image area, like an Image Control or IntelliTrax. The standard has been determined as achievable with the stock+ink combination during process calibration long ago. Pulls are made as the press is running. The scanning spectro scans and compares the data to the standard and if it is too far from it, sends ink key adjustments back to the press console. This is the density move. More density or less density as explained in the document I uploaded.

Measuring LAB at the press lets them know they aren't able to hit the standard. This is what I'm doing with the data. Measuring only density would allow them to continue undetected. If they can't hit the standard based on spectral data with that ink-stock, then you should find out what they can hit, then adjust proofing accordingly. Once you know what they can hit, setup a new process standard, based on spectral data and hold them to it. This is the SOP. The standard doesn't have to be an international standard, as long as they can match proofing. As long as digital can simulate correctly. As an added bonus, LAB at the press could catch problems with maybe ink that isn't to standard, units being contaminated from a previous run, or stock color being inconsistent with what you've ordered in the past.

I still don't think cyan will shift in b* only.