L more than 100

[cementary]

In one application, which measures color with i1Pro 2 in scan mode, i'm getting strange results in paper measurement.
Same paper receives L measurement from 103 to 107, but the same paper in "measure tool", measured with same instument and measured with eXact (M0) receives same L 94.4-94.8.
So spectrophotometer is "ok", i guess.
Could "specular reflection" be responsible for L-values more than 100? If yes, could you explain theory behind this?

 

[Deleted member 16349]

In one application, which measures color with i1Pro 2 in scan mode, i'm getting strange results in paper measurement.
Same paper receives L measurement from 103 to 107, but the same paper in "measure tool", measured with same instument and measured with eXact (M0) receives same L 94.4-94.8.
So spectrophotometer is "ok", i guess.
Could "specular reflection" be responsible for L-values more than 100? If yes, could you explain theory behind this?

It is possible to get values of L that are greater than 100 due to UV or other light providing extra light coming back to the instrument due to fluorescence. Optical brighteners in the paper or ink will radiate light in a different wave length from say the UV light hitting the substrate. The extra light is not due to reflection, it is a form of luminescence.

If you calibrate the instrument to a tile or paper that does not have these Optical Brighteners this can lead to the situation where you get more light coming to the instrument when you measure some particular paper that has the OBs.

If an instrument has a filter that does not allow UV light, then this would help prevent the higher than normal L value.
Also if the instrument does not have a UV filter but its light source does not have much UV, then also you would probably not get the higher than normal L value. Subtle differences in how the instruments are designed can cause different results.

OBs are a real measuring problem because there is no clear answer as how to deal with them.

I am sure Gordon will add to this. I hope he does since he has quite a bit of experience in this area.

Now after a few days you come back and comment that you actually dropped the instrument and it went down the stairs a great distance and maybe broke it, well then my explanations is not probably the right one for you.

 

[cementary]

OBs are a real measuring problem because there is no clear answer as how to deal with them.

I'm sure they are, but:
One and same instrument i1pro2, calibrating on factory tile, working in M0 mode, no uv-filter:
1. With colorflow 1.2.6.5 in scan mode shows L 107.8
2. with measure tool shows 94.4

Same paper, measured with eXact adv in spot mode (M0 condition) shows L 94.39

According to occam's razor principle: simplest answer is best answer, for this particular situation i guess it's difference is in measuring modes: spot and scan.
I can't remember exactly, but i think i've read that specular reflection can provide this effect, maybe in seymour's paper, or blog – can't find it right now.
Maybe i'm wrong, but if it would be about fluorescence and OBA's (while i'm sure this particular paper has) scan and spot measurements would be the same?

Now after a few days you come back and comment that you actually dropped the instrument and it went down the stairs a great distance and maybe broke it, well then my explanations is not probably the right one for you.

Instrument is ok (both of them), i can assure you ))))

 

[Deleted member 16349]

I'm sure they are, but:
One and same instrument i1pro2, calibrating on factory tile, working in M0 mode, no uv-filter:
1. With colorflow 1.2.6.5 in scan mode shows L 107.8
2. with measure tool shows 94.4

Same paper, measured with eXact adv in spot mode (M0 condition) shows L 94.39

According to occam's razor principle: simplest answer is best answer, for this particular situation i guess it's difference is in measuring modes: spot and scan.
I can't remember exactly, but i think i've read that specular reflection can provide this effect, maybe in seymour's paper, or blog – can't find it right now.
Maybe i'm wrong, but if it would be about fluorescence and OBA's (while i'm sure this particular paper has) scan and spot measurements would be the same?


Instrument is ok (both of them), i can assure you ))))

I just suggested one possibility. Of course there might be others that make perfect sense. Hopefully Gordon will make a comment because I would be interested too in what was the cause.

Maybe it has something to do with what mode you calibrate in and what mode you measure with. I am curious about the cause and I hope you let us know when you find out. Good luck.

 

[arossetti]

What measurement mode is the i1pro in during scan mode? M0?

 

[cementary]

What measurement mode is the i1pro in during scan mode? M0?

Yepp, see post #3

 

[Schnitzel]

What are the full CIELab values of the two measurements? Is there a color shift too, or just lightness?

I don't believe OBA could provide 13 units of lightness - that's just too much. Lightness in CIELab is computed only from the Y component of CIEXYZ, and OBA generally tend to increase the Z component (the blue end of the spectrum).

I'd put it down to some sort of software bug maybe?

 

[cementary]

What are the full CIELab values of the two measurements? Is there a color shift too, or just lightness?

I don't believe OBA could provide 13 units of lightness - that's just too much. Lightness in CIELab is computed only from the Y component of CIEXYZ, and OBA generally tend to increase the Z component (the blue end of the spectrum).

I'd put it down to some sort of software bug maybe?

ok, from colorflow: L 106,7 | a 1.2 | b -6.9 – averaged from 3 patches
from measure tool: L 94.4 | a 0.9 | b -7.4
from exact: L 94.39 | a 0.89 | b -6.99

i didn't mention before: uncoated stock 100g, self-baking

PS same stock, but 120g 2 months ago had "norm" L 94.2, so maybe it is a bug

 

[Bret Hesler]

The only times I have seen that with an Eye-one in reflective mode, is when it is not seated properly on the calibration plate. I have not had it happen with an i1Pro2, but had it happen today with an older i1Pro.

 

[Schnitzel]

Maybe ColorFlow has some bug related to the averaging in scan mode? Is that the mode where you measure entire strips of patches in one go?

Can you measure in spot mode in all programs and compare the results? Try to measure the calibration tile itself instead of the paper. You should get a very repeatable result, regardless of the measurement mode used.

 

[cementary]

Maybe ColorFlow has some bug related to the averaging in scan mode? Is that the mode where you measure entire strips of patches in one go?
Can you measure in spot mode in all programs and compare the results? Try to measure the calibration tile itself instead of the paper. You should get a very repeatable result, regardless of the measurement mode used.

Spot mode is not supported in our version of ColorFlow.

Got an answer from product support: "instrument is not well calibrated to it’s white calibration tile".
checked device twice and with new measurement result was 94.0 | 0.8 | -7.0
So "case is closed" thanks to everyone.