Black backing, white backing???

[BeauchampT]

Ok colour management gurus - I'm feeling particularly ignorant today.

My plant is seeking to run to match ISO 12647. I've been noticing that I can never quite achieve my colour gamut needed for paper type we run (although our matches to proof are really decent). Then I looked more closely at the notes I had from the original help we got with implementation and reread the standard as well.

When we were originally trained on how press should implement this colour management, we were told to measure on a BLACK backing. It was explained that we would do this when printing both sides of sheet (somehow it eliminates any reading of print on other side of page???). So, this is what we do. We have a matt black backing on our colour console for all our readings. Never match the gamut required.

I looked at the numbers we in the ISO standard and noticed that there are target values for both WHITE and BLACK backing. So, I tried measuring the same press sheet on both types of backing - WHITE was perfect, BLACK was off (a delta E of 5 with my solid magenta patch).

What sort of backing should I be measuring on? Black or white?

[meddington]

What sort of backing should I be measuring on? Black or white?

White for color management measurements, black for process control measurements...presuming you are printing two sides of the sheet. The reason is as you've stated. Black backing reduces show through/effects from the other side of the sheet. Depending on the opacity of the stock, this may be more or less of an issue. When you say your solid magenta is 5 delta E off when measuring over black backing, are you comparing your measurement to the given ISO Magenta CIELab value for magenta over black backing? Again, Opacity of the sheet will play a roll, as certainly will the shade of the paper to begin with.

[rich apollo]

What Mr. Eddington said.

The black backing avoids the uncontrollable influence from printing on the reverse side of the sheet. Instead you attempt to maintain a consistent influence on the color readings. It's kind of the least of two evils.

If your magenta solid is 5 ∆e off of your target that's fine, as long as it always measures the same. CONSISTENCY, not accuracy, is the most important concept in color management, process control, and printing.

If you want to move to white backed measurements, and you're working in sheetfed, you could try putting the colorbars at the gripper on one side of the sheet, and the tail of the other side.

[meddington]

You could also follow Rich's default advice to all color management issues and convert everything to grayscale.

[meddington]

If you want to move to white backed measurements, and you're working in sheetfed, you could try putting the colorbars at the gripper on one side of the sheet, and the tail of the other side.

Works for sheetwise, but not for work&turn/tumble.

[BeauchampT]

To clarify with a better example of my issues....

Take a solid yellow patch that we print and meausure it with a black backing - Delta E off the ISO target value of around 5 - 6 and a delta in the hue of over 2.5 (swings significantly to the green).

Measure the same patch with white backing (and to confirm we are two sided printing - web press) and the delta H is gone completely and the saturation is almost perfect. An overall Delta E of 1 - 2.

A similar pattern occurs with our other inks.

Now, do we make a stink to our ink manufacturer that we need an ink with better colour strength, or is it simply the way we are measuring is slightly misleading? I don't want to go skipping down the garden path with our ink when we may be doing just fine.

[meddington]

If you ink is ISO 2846 compliant and you hit the ISO 12647-2 targets for white backing, your probably fine, but you can always ask your ink rep these questions. What's the CIELab value of your black backing?

[rich apollo]

You could also follow Rich's default advice to all color management issues and convert everything to grayscale.

Hey! We print TWO colors, black AND white!!

BeauchampT - sounds like you're fine. You might have to adjust something if you had to demonstrate compliance. If you're running on web presses then you can stagger the colorbars off of one another and use white backing for measurement.

Heck, I can't believe you get to use colorbars at all!

[meddington]

Hey! We print TWO colors, black AND white!!

and yet I hear you still have registration issues.

[Kaoticor]

To clarify with a better example of my issues....

Take a solid yellow patch that we print and meausure it with a black backing - Delta E off the ISO target value of around 5 - 6 and a delta in the hue of over 2.5 (swings significantly to the green).

Measure the same patch with white backing (and to confirm we are two sided printing - web press) and the delta H is gone completely and the saturation is almost perfect. An overall Delta E of 1 - 2.

A similar pattern occurs with our other inks.

Now, do we make a stink to our ink manufacturer that we need an ink with better colour strength, or is it simply the way we are measuring is slightly misleading? I don't want to go skipping down the garden path with our ink when we may be doing just fine.

If your process color is swinging to a green, and using a white backing brings it back to center, it could be that your white backing is actually slightly on the blue side and pulling your measurement back to center (depending on the hue error, you can see below that it will be inclined to shift in that direction). This could be additional variation depending on the opacity of your paper that you are using as well. Just a possibility.