Is it possible, to make sure there will be no metamerism under non normalized light?

[ASchuett]

Hello everyone,

let me explain my problem: Today I had a discussion with my colleague about the appearance of a specific orange tone. This tone had been printed on an offset machine in the past. Today I had to produce some flyers in exactly the same orange tone on a Xerox machine. It took me a lot of effort but in the end the orange printed on Xerox looked exactly like the orange printed in offset when viewed under D50 norm light.

Now we come to the point of our discussion: The flyers were brought to an office room with some kind of energy efficient light bulbs. In the office room, there is clearly some metamerism showing. It makes exactly this orange under these specific light bulbs on exactly that kind of paper that we used (lots of fluorescent whitener) look different. The effect can only be seen on the samples, printed on Xerox, not on the offset prints.

My point of view is: This is exactly why we use standardized D50 norm light to view color samples. We should just ignore the metamerism as it will appear only in this single office room, and nowhere else. It`s just a bad luck combination of circumstances. The offset prints might as well show metamerism if you took any other kind of nasty light source. Maybe, to satisfy our client, we should try a different kind of paper for this job and the problem will be solved.

My colleagues point of view is: It's the Xerox machines fault. We should have bought a laser printer from another vendor.

 

[Kent Chung]

The factors of achieving "no metamerism" under "non-standardized" lighting between two sets of printed matters includes the "Ink" and "Paper". The machine used to lay down this layer of ink on top of the paper does not matter because it is only the printed sheet that gets to the client. Therefore, if you can find another digital machine that uses a set of ink that has the same spectral reflectance properties as your original offset printed matter, it is then possible to make sure that there will be no metamerism under any lighting. The probability of finding that pigment/ink set is very small though.

KC

 

[gordo]

Proofs for offset presswork and offset press sheets are intended to form a metameric pair under a specific lighting condition e.g. D50 or D65. When you "matched" the Xerox orange to the offset orange you created a metameric pair under a specific lighting condition. When the lighting condition changed - i.e. samples viewed under office lighting - you experienced "sample metameric failure". That metameric failure is due to the different spectral response curves of the two samples.
You also have a failure to set correct customer expectations about the integrity of the "match" since the likelihood of two samples with different spectral response curves forming a metametric pair under more than one lighting condition is pretty much zero.

 

[David Milisock]

My colleagues point of view is: It's the Xerox machines fault. We should have bought a laser printer from another vendor.

Well that's a load of crap, this is a common problem even print paper and ink does the same thing, managing the client expectations is the only answer. You should try making solvent printed graphics, color management is a technology that is awesome and very helpful but there is no technical solution except managing the client for this issue.

 

[ASchuett]

Thanks for your reply, everyone.

the likelihood of two samples with different spectral response curves forming a metametric pair under more than one lighting condition is pretty much zero.

I think that describes the problem pretty good. The kind of formulation I was searching for.

 

[davarino]

Thanks for your reply, everyone.

I think that describes the problem pretty good. The kind of formulation I was searching for.

Which of course brings us back to the underlying problem: managing expectations.

Show me the salesperson who can confront this level of ignorance and swinish willfulness constructively and I will show you a salesperson who is very unusual.

Yet, if a customer is unwilling to accept this very simple truth that the likelihood of two matches is near zero, it will be impossible for him to accept that the best is being done for him.

 

[D Ink Man]

I would suggest that you and your customer should agree under what light source you can use for acceptable color for comparison. No matter what, metamerism will exist in this case scenario. Offset printing inks are made from pigments and Xerox toners are normally made from dyes.

Knowing this and explaining it to your customer should shed some light on the conundrum and provide an amiable understanding.

D Ink Man

 

[Correct Color]

Probably just being picky here, but...

Metamerism is when it works.

Metameric failure is when it doesn't.

 

[D Ink Man]

Metamerism in simple layman terms, is the appearance of a color looking different under different light sources. And no, it is not good or something that is working right. It is something that exists that we oft times have to deal with.

D

 

[Tim-Ellis]

Wikipedia....

"In colorimetry, metamerism is a perceived matching of the colors that, based on differences in spectral power distribution, do not actually match. Colors that match this way are called metamers."

"The term illuminant metameric failure is sometimes used to describe situations where two material samples match when viewed under one light source but not another."

 

[gordo]

Wikipedia....

"In colorimetry, metamerism is a perceived matching of the colors that, based on differences in spectral power distribution, do not actually match. Colors that match this way are called metamers."

"The term illuminant metameric failure is sometimes used to describe situations where two material samples match when viewed under one light source but not another."

I think this is a good thread. It's important to make sure that technical terminology is used correctly and that everyone is on the same page as far as understanding the impact of metamerism in the graphic arts.

"Sample metameric failure", or as Wikipedia calls it "illuminant metameric failure" is the most common issue faced in the graphic arts and is the one discussed in this thread. However there are other types of metameric failure that can occur.

"Observer metameric failure" can occur because of differences in color vision between observers. The common cause is colorblindness however it is not uncommon among "normal" observers - e.g. press operator and client at a press approval. As a result, two spectrally dissimilar color surfaces may produce a color match for one person but fail to match when viewed by another person. This often shows up when trying to align presswork to a proof.

"Field-size metameric failure" occurs with colors that match when viewed as very small, centrally fixated areas but may appear different when presented as large color areas. This is the reason why color painted on a wall may appear different than the paint chip used to select the color even though they match when the chip is placed on the wall. In print production field-size metameric failure typically occurs when small PMS swatchbook samples are used to specify a PMS color that will cover a large press sheet area.

"Geometric metameric failure" results in identical colors appearing different when viewed at different angles, distances, light positions, etc. This happens because material attributes such as translucency, gloss or surface texture are normally not considered in color matching. Geometric metameric failure is most often seen when using metallic inks or paper, and specialty ink coatings or papers.

 

[Correct Color]

Metamerism in simple layman terms, is the appearance of a color looking different under different light sources. And no, it is not good or something that is working right. It is something that exists that we oft times have to deal with.

I know that's what many people in this industry think it means...

But as pointed out above, that's actually exactly backwards.

 

[michaelejahn]

No Title

you might enjoy;

http://www.mondigroup.com/printing/uploads/StandardViewingConditions_678_EN.pdf

 

[Bob_McC]

Metamerism is a little like Murphy's law ... it often occurs when you least want it.

The Graphic Arts & Photographic industries decided many decades ago (mid 60's as British Standard BS-950 or early 70's as ANSI PH-2030) that the materials used in printing and photographic reproduction were not highly susceptible to metamerism (e.g. had comparable spectral reflectance curves) so critical color evaluations and color approvals could take place under a single light source (D50). [side note: since process color printing was mostly being produced on one and two color presses back then, there was an additional light source (D75) specified for use in the press room to allow easy detection of color shift with the yellow printer. The D75 is a bluer simulation of natural daylight and made it easier to see the yellow ink on white paper. D75 was removed from the ANSI standard in the 1989 version of PH2.30.

This has worked quite well for the industry except for packaging, digital printing, textile printing, and any other graphics application that uses colorants and substrates with different reflectance characteristics. In this case there is a good argument to be made to incorporate multiple light sources (with different spectral power distributions) to visually check a color match. This is the norm in nearly every other color critical industry (plastics, textile, paint coatings, food for example). Viewing booths are available that provide D50 along with two additional light sources (typically Incandescent A and Cool White Fluorescent) to allow you to confirm an excellent (non-metameric) color match plus put on your 'aesthetic evaluation' hat and see what the color will look like in a "real world" (store or home) location.

The comments posted earlier are correct. The metamerism you experienced is a result of the differences between the toner based inks and substrate used in your Xerox printer and the pigment based inks and substrate used on the offset piece. Checking the color match under a multi-light source viewing system will inform you of the issue and the degree of mis-match that will occur, but does not change the basic physics of what is happening.

Here are a couple related technotes on this subject.

 

[DeltaE]

Dear All Experts,

I read this topic and it is really interesting. May I have a question (could be a stupid question ^_^) that:
- When I try to mix a spot color to match with a sample in offset printing. Standard light source is D50.
- With my Xrite eXact handheld spectrophotometer, I can compare my spot color and the sample, and I also can get the metamerism index value between D50 and several light source such as D65, A,.... So my question is: beside Delta E (D50/2) is very small (<1), if the metamerism index values are very small (<0.5), could I make a conclusion that my own spot matched to the sample very very well or their spectrum could be almost the same?

Thanks in advance, wish you all a great working week!
Regards,
DeltaE

 

[Deleted member 16349]

Dear All Experts,

,.... So my question is: beside Delta E (D50/2) is very small (<1), if the metamerism index values are very small (<0.5), could I make a conclusion that my own spot matched to the sample very very well or their spectrum could be almost the same?

Thanks in advance, wish you all a great working week!
Regards,
DeltaE

Interesting way to ask the question. No "or". It is just about matching the spectrum.

As a non expert, I would say that if you get a match in under several illumination conditions, then you have probably closely matched the reflected spectrum of the two samples.

It may have happened by luck since I think it would be hard to match spectrums of most colours this way with a limited set of spot (mixing) colours. Since inks act as filters to light and filter differently over the whole spectrum, it is difficult to modify the spectral curve in specific areas. Theoretically if you had a large set of mixing inks that had very localized filtering of light, it would be possible to fine tune the final ink to have a matching spectral curve. But with real inks, there is always the situation where you want to adjust the curve in one location only but the real inks also affect other locations along the curve.

Printing is based on metameric matching since it is more achievable even though spectral matching would be ideal but it is not yet practical with inks.

One also has to remember that matching does not mean the colour is the same under different lighting conditions. Even a spectral match, which would show a match between two samples under different lighting conditions, would not be the same colour between the different lighting conditions. A goal of trying to have the same colour under all lighting conditions is not a realistic goal.