Help with magenta/green crossover

[paula_goldman]

Your brightest highlight in the capture is a good stop or more from clipping.

You should reshoot, bracket 1, 1.5, 2 and 2.5 stops more, then examine the raw in a demo of RawDigger. Then you'll know exactly how to target the exposure.

 

Sadly, that is impossible.

I have some hotter exposures that I'll look at.

Getting that article and learning about RawDigger was [almost] worth it.

Thanks again.

[rodeo_joe1]

BTW. Those Kodak strips must be pretty ancient by now, and apart from the stepwedge area, they only use cheap CMYK printing. So really the camera's only looking at 3 different colours + black.

 

You might want to update your colour swatch to one that uses a wider range of spot colours.

 

Those old Kodak things were OK in the days of film, but they're definitely only in the 'better than nothing' category now.

[rodeo_joe1]

Correction to the above:

I just examined my most recent version of Kodak Colour Separation Guide using a loupe. The colour patches are indeed spot colours, but they're very blotchy, with the white base showing through and some density variation streaks. In short, not very carefully produced.

 

AFAIK, Kodak never issued a photometric analysis of those colours, which makes the swatch less useful than, say an IT8.7, or a Gretag-Macbeth colour target.

 

Personally, I'd be happier with a fistful of paint sample swatches from a DIY store. Still no photometric data, but at least they're solid colour and not blotchy!

[paula_goldman]

Correction to the above:

I just examined my most recent version of Kodak Colour Separation Guide using a loupe. The colour patches are indeed spot colours, but they're very blotchy, with the white base showing through and some density variation streaks. In short, not very carefully produced.

 

AFAIK, Kodak never issued a photometric analysis of those colours, which makes the swatch less useful than, say an IT8.7, or a Gretag-Macbeth colour target.

 

Personally, I'd be happier with a fistful of paint sample swatches from a DIY store. Still no photometric data, but at least they're solid colour and not blotchy!

 

Yes, I know, I put them there out of habit. I use a Color Checker passport, but it's too small for these giant paintings. I made 3 different lighting profiles for my different setups (moved the camera), and was really surprised that they had very little effect when I was processing. I've learned I need to pay more attention to exposure...

[rodeo_joe1]

I'm not sure any kind of visible reference would help with fluorescent colours or coatings.

The effect on the sensor is going to heavily depend on the UV content of the light source. Bringing it all down to suck-it-and-see.

 

I think shooting RAW - for the colour balance - and a wide range of bracketing is the most sensible approach for this particular subject.

 

It's all going to be open to interpretation anyway, unless the artist has specified a very particular UV-rich light source and viewing conditions for the artwork. You probably just have to go with what looks right to the client..... but that most likely won't include mauve patches. :rolleyes:

[paula_goldman]

I'm not sure any kind of visible reference would help with fluorescent colours or coatings.

The effect on the sensor is going to heavily depend on the UV content of the light source. Bringing it all down to suck-it-and-see.

 

I think shooting RAW - for the colour balance - and a wide range of bracketing is the most sensible approach for this particular subject.

 

It's all going to be open to interpretation anyway, unless the artist has specified a very particular UV-rich light source and viewing conditions for the artwork. You probably just have to go with what looks right to the client..... but that most likely won't include mauve patches. :rolleyes:

 

Welcome to my life. They're getting 3 versions with different levels of fluorescence.

They cleaned up pretty well, though my hourly fee works out to 5 cents.

Thanks, Rodeo Joe!

[AJG]

Yes, I know, I put them there out of habit. I use a Color Checker passport, but it's too small for these giant paintings. I made 3 different lighting profiles for my different setups (moved the camera), and was really surprised that they had very little effect when I was processing. I've learned I need to pay more attention to exposure...

One thing I do with large paintings and the small color checker is to move the camera in after shooting to get a close up before I have changed the lighting or the lens on the camera. Sometimes I will have the artist hold it in front of the painting.

[paula_goldman]

One thing I do with large paintings and the small color checker is to move the camera in after shooting to get a close up before I have changed the lighting or the lens on the camera. Sometimes I will have the artist hold it in front of the painting.

Yes, that's what I did. Thanks

[digitaldog]

AFAIK, Kodak never issued a photometric analysis of those colours, which makes the swatch less useful than, say an IT8.7, or a Gretag-Macbeth colour target.

Kodak Color Separation Guide - deltaE

Kodak Gray Scale - deltaE

They are blotchy in the photo. You don't know if they are actually blotchy. The capture is pretty massively under exposed and pretty noisy due to that.

[paula_goldman]

Kodak Color Separation Guide - deltaE

Kodak Gray Scale - deltaE

They are blotchy in the photo. You don't know if they are actually blotchy. The capture is pretty massively under exposed and pretty noisy due to that.

 

You are both right, and I suppose good to know that even at my age I have plenty to learn.

 

Thanks very much, and wherever you are, enjoy what’s left of Mardi Gras.

[rodeo_joe1]

"The target has a half toned set of colors..."

 

I think this was true of early editions, but the late Q13 version I have consists of lithographed spot colours. The colours themselves are not very constant in density across the patches, and the stippled lithography shows the white (plastic?) base through the ink. This is examining the 'control' patches directly from the target under a loupe.

You don't know if they are actually blotchy

- Mine are actually blotchy on the original target. The darker red patch especially shows some density streaks; it doesn't appear to be from physical damage, but from faulty screening.

[digitaldog]

"The target has a half toned set of colors..."

 

I think this was true of early editions, but the late Q13 version I have consists of lithographed spot colours. The colours themselves are not very constant in density across the patches, and the stippled lithography shows the white (plastic?) base through the ink. This is examining the 'control' patches directly from the target under a loupe.

 

- Mine are actually blotchy on the original target. The darker red patch especially shows some density streaks; it doesn't appear to be from physical damage, but from faulty screening.

Your target isn’t his target. If it’s half screen or not is moot. Further it doesn’t matter if it’s blotchy or not. Whatever that supposed to mean.One can average a sampling of the color squares and produce Lab values. That’s the key usage of the product digitally. The original posters target clearly shows in Rawdigger how underexpose the image is. That’s the first problem in this capture.

Edited March 6, 2019 by digitaldog

[digitaldog]

AFAIK, Kodak never issued a photometric analysis of those colours, which makes the swatch less useful than, say an IT8.7, or a Gretag-Macbeth colour target.

!

 

The IT8/Q60 was never designed for the tasks seen with the Kodak Q12 and Q13 targets that WERE designed as outlined in the previous URL I provided: for helping photographers compare the color of the subject with known printing colors. The IT8 was disingned for creating ICC profiles. Later to characterize 4 color printing; some facts:

 

IT8 - Wikipedia

ColorWiki - Kodak IT8 (Q60) Targets

 

There happen to be differing IT8/7 targets FWIW 7/1,7/2 and 7/3. The IT8 comes in many flavors so to speak; differing reflective paper stocks and transparencies (differing emulsions and kinds of film or paper). As such, it comes with a TDF or Target Description File, a text file with measurements of each color patch in Lab or similar device independent color space device values. The TDF can be individually measured per target (VERY expensive, I have several) or it's a measurement of an average of the stock and production of IT8/Q60s.The TDF lot number is usually part of the text found on the actual target.

 

The very idea of photographing an IT8 without having an associated TDF, or using it to decipher the dE (color distance/difference) between captured target and TDF is a massive waste of time. It absolutely is not the right target to be using for reproduction photography short of usage for creating ICC profiles. And today, there are MUCH better targets for the creation of ICC profiles for digital cameras, the IT8/Q60 isn't appropriate for that kind of work! X-rite makes several, GretagMacbeth doesn't exist nor has existed for many years (they are now rolled into X-rite who owns Pantone and Macbeth). These are the family of ColorChecker targets (SG or DC specifically).

 

For reproduction work, where a photographer needs a color reference, the Q12 and Q13 is absolutely appropriate. A Macbeth 24 patch ColorChecker (the correct name for this target) is a bit better as one can if so desired, build a custom .dcp profile in raw converters that support this kind of camera profile. And of course, it comes with a TDF. A history lesson about this specific MacBeth ColorChecker:

The ColorChecker Pages (Page 1 of 3)

[rodeo_joe1]

The original posters target clearly shows in Rawdigger how underexpose the image is. That’s the first problem in this capture.

But the image contains fluorescent 'whites' that are clearly reproduced brighter than the 'white' patches on the Kodak target. That's the problem.

 

And I fail to see how any target that has no (official) data file can be of much use in digital reproduction. Nobody sends their film to be scanned and separated for CMYK printing anymore. ICC profiles are king.

 

And the Kodak target doesn't use SWOP colours but spot pigments. So it isn't even much use for matching CMYK printing inks.

Your target isn’t his target.

Exactly! Those old things were obviously fairly sloppily and inconsistently reproduced.

Edited March 7, 2019 by rodeo_joe|1

[rodeo_joe1]

Old and even-older versions of Kodak Colour Sep. Guides.

Not even close to each other at any colour!

 

Both sets have been stored in their original packaging in the dark, and with acid-free paper separators around them.

[digitaldog]

But the image contains fluorescent 'whites' that are clearly reproduced brighter than the 'white' patches on the Kodak target. That's the problem.

.

No, it's not, The problem is two fold: the entire image is massively under exposed. The other is a misunderstanding of how the target is used.

[digitaldog]

Old and even-older versions of Kodak Colour Sep. Guides.

[ATTACH=full]1286075[/ATTACH]

Not even close to each other at any colour!

Both sets have been stored in their original packaging in the dark, and with acid-free paper separators around them.

 

Are your misunderstandings about these targets such you believe they never fade or need replacement? Did you actually read what's printed on the instructions or the covers of the products as I have?

http://digitaldog.net/files/Q60.jpg

Do you not have any tools to measure the patches and compare them to the Lab references? Seems you do not.

Do you actually believe the white patch should be used for exposure (no) or that it's more telling than the entire raw histogram of the OP's capture? (again, no).

[digitaldog]

Old and even-older versions of Kodak Colour Sep. Guides.

Not even close to each other at any colour!

What's not even close is the evenness of the lighting of your two targets. The Lab value samplers are shown (#3 and #4) in the left side of my screen capture with a 5x5 sampling. You're off an Lstar of 77 vs. 72! A dE of 3.72 in uneven lighting. Gray paper (-2 a and b star) isn't neutral either so who knows if the capture is....

 

The two white patches are a dE 2000 of 3.85. Part of the delta is due to the uneven lighting outlined colorimetrically above. Part is due to the yellowing of one of the white's (-4 bStar).

 

Some colorimetric facts:

http://digitaldog.net/files/Q60dE.jpg

Maybe these targets were purchased just after the Earth started cooling. :D But it illustrates you need to buy new ones....

Edited March 7, 2019 by digitaldog