OBC functionality in iProfiler is VERY BADLY programmed! how to bypass?

[Robert Ardill]

Well no - that's the point of FWA compensation, it compensates for the fact that the instrument illuminant relative UV level is different from that of the viewing illuminant. If they are the same (i.e. both incandescent), then yes, FWA compensation isn't needed.

Yes, I got a little confused there .  I have a couple of follow-up questions though.

1. If the target illuminant has a higher UV content than the measuring instrument, can OBA compensation correct for the shift in colors (other than white).  For example, a pale yellow will fluoresce, even if the ink does not, because of the underlying paper: does the Argyll OBA compensation correct for this?  It would seem difficult to be able to estimate the extent to which the ink has blocked out the paper.

2. Would a dual-scan with/without UV not give a much more precise estimate of the fluorescence than a single estimate based on the spectral shape of reflected white?; and make it possible to fairly accurately compensate on the full gamut of colors? 

i1Profiler allows for 2. above, followed by a selection (or measurement) of the target illuminant.  The problem though is that the instrument can't measure UV directly, so I don't see how it would know the UV content of the (measured) target illuminant.  Even if a standard illuminant is chosen (say F1), the spectrum shown only goes from 380nm.

Robert

[JRSmit]

Yes, I got a little confused there .  I have a couple of follow-up questions though.

1. If the target illuminant has a higher UV content than the measuring instrument, can OBA compensation correct for the shift in colors (other than white).  For example, a pale yellow will fluoresce, even if the ink does not, because of the underlying paper: does the Argyll OBA compensation correct for this?  It would seem difficult to be able to estimate the extent to which the ink has blocked out the paper.

2. Would a dual-scan with/without UV not give a much more precise estimate of the fluorescence than a single estimate based on the spectral shape of reflected white?; and make it possible to fairly accurately compensate on the full gamut of colors? 

i1Profiler allows for 2. above, followed by a selection (or measurement) of the target illuminant.  The problem though is that the instrument can't measure UV directly, so I don't see how it would know the UV content of the (measured) target illuminant.  Even if a standard illuminant is chosen (say F1), the spectrum shown only goes from 380nm.

Robert

Even if the UV part of the illumination is measured, how to correlate that to the reflected result of given paper?

The measurement devices as i1 Pro2 have their own illuminants

[Robert Ardill]

Even if the UV part of the illumination is measured, how to correlate that to the reflected result of given paper?

The measurement devices as i1 Pro2 have their own illuminants

Well, the measurement could compare spectrum of the illuminant, measured directly, to the spectrum of the reflected white (as does Argyll). But what about the effect of different ink densities and colors on the target paper?

Also, how can the i1Pro2 measure the UV in the target illuminant? ... it can't do it directly; Argyll measures it indirectly by comparing the spectrum of the illuminant to the spectrum of the reflected white ... does i1Profiler do the same?  There seems to be a lot of guesswork needed on our part (or perhaps there's documentation somewhere that explains this in full detail using English rather than CIE-speak).

Robert

[Robert Ardill]

Great for the graphic industry, but what about the individual observer? Then just M0, M1, M2 does not work out of the box, you have to have some way of applying a compensation though trial and error to come to an acceptable result.

Do you say this because for an individual observer we have no way of knowing for sure what the illuminant will be, whereas in the graphic arts the illuminant will be D50?  If so, what about displaying in a gallery, say, where the illuminant is known or can be measured (but may not be D50)?

Robert

[digitaldog]

Do you say this because for an individual observer we have no way of knowing for sure what the illuminant will be, whereas in the graphic arts the illuminant will be D50?  I

Well that's one assumption (there are all kinds of ways to view a print we are told are "D50").

There are at least two light sources at play here and often more. The Light source in the measuring instrument and the light source used for viewing the print with all those OBA's (how much?)

In the old days we had basically two options. One was to include the UV, the other was to filter it out. Some would say filtering out, 'ignoring' the UV's affect on the measurement data was dumb. Other's would say it only makes sense to filter it out. And neither approach deals with the 2nd light source; where the print is being viewed.

What X-rite did was provide a method of visually 'tweaking' a profile based on viewing output under the conditions where the final print will be viewed and comparing it with their targets of gray patches with numbers one inserts into the software for dog knows what compensation. Then you visually compare the two. I think, like the idea of a good profile editor (where you work visually, not numerically where sometimes we do get into trouble with visual mismatches), makes sense. This is kind of what's happening here.You have to view the X-rite supplied target and what you print from the profiles side by side, on-site where you wish to view the prints for that compensation just to enter a value into their software.

As to what is affected, pretty sure all colors are affected to some degree and differently depending on the 'compensation' and when you use the X-rite OBA target thingie, it's a group of gray patches you visually examine to decide what compensation if you will, the new profile will undergo.

In the end, it's a mess which causes more work but would all be avoided if you just cease using papers with high OBA's and control how the print is being viewed, something that isn't always possible.

I just built a customer a profile from HanaPhoto Luster 260, the paper white had a bStar of -9.13! For fun I tried running it through ColorAnt using max Brightener compensation (100) and the resulting bStar was 0.39! I can't handle any of this X-rite compensation stuff, the client is in Peru! I provided a profile both ways, he reported that the one with compensation was subtilely better (so nothing super dramatic here). But I have no idea how he's going to view the prints or where and asked him to try different lightning conditions for both profiles. Again, he preferred the one 'fixed' by running the measurement data through ColorAnt. For remote work, that's about the best I can do. And with a bStar of -9, I suggested he find another paper to use! He originally sent me 5 papers to profile and all but this one Luster paper either had no OBA's or tiny amounts.

[Robert Ardill]

What X-rite did was provide a method of visually 'tweaking' a profile based on viewing output under the conditions where the final print will be viewed and comparing it with their targets of gray patches with numbers one inserts into the software for dog knows what compensation. Then you visually compare the two. I think, like the idea of a good profile editor (where you work visually, not numerically where sometimes we do get into trouble with visual mismatches), makes sense. This is kind of what's happening here.You have to view the X-rite supplied target and what you print from the profiles side by side, on-site where you wish to view the prints for that compensation just to enter a value into their software.

Do you think that the XRite visual approach is better than the dual-scan approach?  I would have thought that with dual-scan the profiling software can see exactly what the fluorescent effect is on all of the colors in the target.  Since the software knows the UV content in the instrument's light, and as we specify the target illuminant (or measure it), the software should then be able to extrapolate to the target illuminant fairly accurately.  For standard illuminants the UV content should be known, but I do have a question about how i1Profiler estimates the UV content of the illuminant from a measurement (since the i1Pro2 cannot 'see' the UV) ... any idea where we could get an answer?

In the end, it's a mess which causes more work but would all be avoided if you just cease using papers with high OBA's and control how the print is being viewed, something that isn't always possible.

Yes, totally.  The question is, how do we know how much OBA is in the paper?  Canson specifies that papers like the Platine have no OBAs, but for other papers like the Baryta there is no mention of OBAs so I assume that the paper will have some (but probably not much as the whiteness will mostly come from the coating).

I just built a customer a profile from HanaPhoto Luster 260, the paper white had a bStar of -9.13!

Nice blue paper .  But a b* of -10 may just show that the paper is blue; it may contain little or no OBAs.  Probably a better estimate would be to look at the tell-tale hump at the blue end of the spectrum (from reflected white).  Argyll's spotread is good for that.

Robert

[Tim Lookingbill]

In my graphic design days back in the '80's I don't remember OBAs even mentioned as a concern when I'ld receive in the mail free tastefully designed paper sample booklets off a commercial offset press showing various sheens and off white hues with beautiful images printed from manufacturers such as Potlatch and others.

Maybe it was my lack of training or exposure to high end graphics productions like corporate annual reports that didn't get me to view these papers under various lights to check how blue they'ld turn. I didn't have a Solux4700K, just window light, tungsten or soft white fluorescent tubes. Never gave much thought to light having any affect on white hues. I always thought the manufacturer was controlling that by specifically naming their papers with names like "Egg Shell", "Natural", "Bone", "Ivory", etc.

I do wonder though now why I have to apply a middle slider reduction in Levels blue channel to make the image more yellow when I use "Printer Manages Color" on Epson Ultra Premium Photo Glossy paper which I found out does have OBA's.

But then I decided to really check out all the varieties of lights around my home that I view my prints and I notice some lights only affect the white of the paper while others leave the white unchanged but produce a strange metameric effect with the ink (LED's excite the cyan ink with pigment based Epson Dura Brite Ultra ink).

Below are shots I took of the same Epson Ultra Premium Glossy paper print under various lights to try to figure out whether the color of light is causing the paper white to change or the paper's OBAs. Now my camera wouldn't record the cyan metamerism of the LED's I saw with my eyes though you might see some slight violet bias in the lower right shadow of the white rose on some. Tungsten of course gave the most flattest and uniform rendering.

So my question is how does anyone detect OBA's visually when it's quite difficult to separate the color of light from its spectral reflectance characteristics in how it excites OBA's?

And can someone post a comparison between two prints of the same image on the same OBA paper using two profiles, one print profile built with OBA compensation and the other without? Is it something similar to my Blue channel Levels slider adjustment to make the print appear more yellow on bluish looking paper?



 

[digitaldog]

Tim, get yourself an LED Blacklight flashlight.

[Tim Lookingbill]

Tim, get yourself an LED Blacklight flashlight.

Andrew, I know why you suggests this as a way to check for OBA's, but then we're right back into the circular logic having to do with why this is practical since we don't view prints under blacklight.

I really don't need to check whether a paper has OBA's. I want to know the extent of whether this is a real issue that needs to be fixed with an ICC profile. I'm seeing a huge disconnect on the visual part of seeing this as a real problem due to not being able to see this visually even on OBA paper.

I can't see how an ICC profile can fixed this moving target as well as for targeting one specific light and OBA paper. It looks like a recipe for madness.

Can someone show how this makes a better looking print?

[digitaldog]

Tim, you can't fix a moving target, I explained this earlier. You can fix a non moving target! The flashlight or a Lab reading can help you detect if you may have an OBA issue.

[Tim Lookingbill]

Tim, you can't fix a moving target, I explained this earlier. You can fix a non moving target! The flashlight or a Lab reading can help you detect if you may have an OBA issue.

But I just said I'm not wanting to check for whether a paper has OBA's.

I want someone to show how this is fixed with an ICC profile with an A/B demo. What does this look like?

[digitaldog]

I want someone to show how this is fixed with an ICC profile with an A/B demo. What does this look like?

It's fixed using a number of options (OBA correction in ColorAnt, the OBA system by X-rite etc). You want me to show you? Come on down, bring your check book, I'll show you. Or you can read the manuals which should be online (ColorAnt is). Or you could just build two profiles each way and view the results from a good reference image under any number of light sources. What does the fix look like? Usually a bit better! Lack of a possible color cast. Build a profile without OBA, print a reference image, VIEW IT under the illuminant. If it's got OBAs that cause a color shift, fix it using the tools available.

This isn't a big issue Tim! I've built hundreds upon hundreds of profiles plus a group for Epson (Exhibition Fiber) so perhaps thousands of people have used those profiles without a lick of OBA compensation. The net isn't filled with Epson users complaining but none the less, the best approach is to use papers without OBA's! And OBA's have negative consequences above and beyond how they appear, they can cause issues in terms of the archival properties and qualities of the print (they change over time). They ain't good Tim! 

We have a system even without OBA's that assume D50 viewing conditions and lots of folks don't view their prints that way. The fix? Like OBA, we measure the light and use that inside the profile instead of the D50 assumption. It helps but like OBA, it's fixing a moving target and the end results are usually subtle. Just as my client with the HUGE OBA paper reported when viewing two prints made from two different profiles.

[GWGill]

Great for the graphic industry, but what about the individual observer? Then just M0, M1, M2 does not work out of the box, you have to have some way of applying a compensation though trial and error to come to an acceptable result.

It doesn't have to be trial and error.

[GWGill]

1. If the target illuminant has a higher UV content than the measuring instrument, can OBA compensation correct for the shift in colors (other than white).  For example, a pale yellow will fluoresce, even if the ink does not, because of the underlying paper: does the Argyll OBA compensation correct for this?  It would seem difficult to be able to estimate the extent to which the ink has blocked out the paper.

Well I can't speak for how others do it, but yes, ArgyllCMS's FWA compensation is spectral, and corrects the colors of the whole profile.

2. Would a dual-scan with/without UV not give a much more precise estimate of the fluorescence than a single estimate based on the spectral shape of reflected white?; and make it possible to fairly accurately compensate on the full gamut of colors?

Yes, having an instrument that can take two measurements with more and less UV provides a better way of estimating the quantum efficiency of the fluourescent agent, as well as its emission spectrum. This has nothing to do with correcting or not correcting a full gamut of colors.

i1Profiler allows for 2. above, followed by a selection (or measurement) of the target illuminant.  The problem though is that the instrument can't measure UV directly, so I don't see how it would know the UV content of the (measured) target illuminant.  Even if a standard illuminant is chosen (say F1), the spectrum shown only goes from 380nm.

As I mentioned before, I'm not a ProfileMaker expert, but my understand is that they print a series of test patches that assumed different levels of UV from the illuminant, and then rely on the user making a visual match to a reference color. This is a different way of extracting similar information about the illuminant, to that obtained using ArgyllCMS's illumread.

[GWGill]

Do you think that the XRite visual approach is better than the dual-scan approach?

I don't think it works that way. My understanding is that X-Rite use both :- dual scan to figure
out what the FWA emission spectrum looks like as well as how that interacts with the
colorants, and the visual matching step is to estimate the UV content of the target illuminant.
Both would then be combined to spectral compensate the whole profile. (At least, that's
how I would be doing it if I were them.)

[GWGill]

So my question is how does anyone detect OBA's visually when it's quite difficult to separate the color of light from its spectral reflectance characteristics in how it excites OBA's?

It's pretty obvious from the spectral reflectance of the paper itself when measured using a non-UV filtered instrument like the i1pro. Non-FWA impregnated paper has a flat spectrum that gently bends down in the short wavelengths. FWA containing paper has peak in the blue that then sharply rolls off as you get to the wavelengths that are being absorbed by the FWA. See http://www.axiphos.com/BrightnessReview.pdf

[Robert Ardill]

I don't think it works that way. My understanding is that X-Rite use both :- dual scan to figure
out what the FWA emission spectrum looks like as well as how that interacts with the
colorants, and the visual matching step is to estimate the UV content of the target illuminant.
Both would then be combined to spectral compensate the whole profile. (At least, that's
how I would be doing it if I were them.)

Yes, i1Profiler does use both of course, as well as measuring (or specifying) the target illuminant.  There's some useful information here: Northlight i1Pro2 Review OBA-Compensation.

Unfortunately, checking out OBA compensation is extremely time-consuming.  What we really need is a clear recommendation on when to use OBA compensation and when not to use it.  Presumably someone, or some organisation, has already done the required testing - in which case it would be good to get the recommendations.

In the meantime it seems to me that the best recommendation is to use papers with no OBAs or very little. 

But then what about the shading agents?  How do we know if a paper has some (I suppose we could look at the spectrum) ... and if we do know, what can we do about them?  What are shading agents used for? Is it an additional mechanism to make the paper look whiter? (by reducing the yellows). Could papers have little or no OBAs but have quite a lot of shading agents, and could these be just as big a problem (as they may affect a wider part of the spectrum, and as we have no mechanism to compensate them out)?

Robert

[GWGill]

But then what about the shading agents?  How do we know if a paper has some (I suppose we could look at the spectrum) ... and if we do know, what can we do about them?  What are shading agents used for? Is it an additional mechanism to make the paper look whiter? (by reducing the yellows). Could papers have little or no OBAs but have quite a lot of shading agents, and could these be just as big a problem (as they may affect a wider part of the spectrum, and as we have no mechanism to compensate them out)?

Because shading agents are just dyes, you don't have to do anything - the normal profiling process takes it all into account. My guess is that shading agents would rarely be used on their own, but typically as an additional component to the FWA in the cheapest types of papers. They are easy to spot as a dip in the paper reflectance in mid wavelengths.

[Robert Ardill]

Yes, having an instrument that can take two measurements with more and less UV provides a better way of estimating the quantum efficiency of the fluourescent agent, as well as its emission spectrum. This has nothing to do with correcting or not correcting a full gamut of colors.

Well, i1Profiler measures every spot color twice (with and without UV) in dual-scan mode.  This means that the effect of fluorescence is known for the whole gamut.  As this information is available, the software could (but perhaps doesn't) apply the compensation for each spot color.  Then it gets the UV content of the target illuminant using the gray card and scales the data up or down as required.

If I understand you correctly, you are saying that the dual scan would give you a better way of computing the spectrum due to the OBA. Why would you need to measure anything except the paper white for that?  

When you say 'quantum efficiency', what do you mean?  Do you mean the varying effect of the UV on each spot color?  If that is what you mean, then would this not be quite useful in correcting the full gamut?

If the full gamut is not corrected using this data, then how is it corrected? For example, how does Argyll do it? (since Argyll, at least currently, does not do a dual scan).

Robert

 

[Robert Ardill]

Because shading agents are just dyes, you don't have to do anything - the normal profiling process takes it all into account. My guess is that shading agents would rarely be used on their own, but typically as an additional component to the FWA in the cheapest types of papers. They are easy to spot as a dip in the paper reflectance in mid wavelengths.

Thanks, that's good to know.

Robert