how do you get delta E readings on clear film

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how do you get delta E readings on clear film

Postby inkroom123 » Tue Aug 26, 2014 3:54 pm

I am trying to find out what the industry standard is for reading color on clear films? right now any reading we take no matter the substrate we back it with a white ceramic tile. I can't find anyone talking about reading on a clear film yet? any ideas?
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Re: how do you get delta E readings on clear film

Postby Frank Burgos » Wed Aug 27, 2014 12:30 am

Measure over a white backing. Tile, paper, plastic or any other material will work, as long as it has the following properties:

When you look at the surface in a normal office environment, there should be no reflection. It should be flat, not glossy. You shouldn't be able to tell, by looking at the surface, that there's a dark picture hanging on the wall, even if you slant the surface every which-a-way. It should not be a mirror.

Now, break out your spectrophotometer and measure the absolute color of the backing surface. You are not comparing color, so be sure that the following values you read are absolute values, not differences:

The L* (lightness) value should be greater than 92
The C* (chroma) value should be less than 3

Those values are simply read off the device, if it's set to L*C*h color space. If you're in L*a*b* color space, and don't want to or can't change, no wahala. Just multiply the a* value by itself, multiply the b* value by itself, add the two together, take the square root, and presto; you've got the C* value. (A shorter way to describe the math is to take the square root of the sums of the squares of a* and b*.) It is legit to translate between color spaces. You just can't make any other changes to your instrument.

In addition, their should be no fluorescence. That said, given that the latest M1 standards, and I'm sure that as an ink guy your device complies, I would imagine the influence of fluorescence would be mitigated.

If you decide to use a black backing, because you have print on both sides of the film, for example, and you can't find a spot over which to measure only the surface print, and you want to mitigate the influence of the back-print, you can do that and not go to jail. The black backing just has to satisfy a set of specifications, just like the white does. If it does, you can actually calculate what the color would be if it were measured over white, if you wanted to.

Finally, it's ideal to always measure over the same backing.

Regards,
Frank
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Re: how do you get delta E readings on clear film

Postby inkroom123 » Wed Aug 27, 2014 10:20 am

Thanks Frank
is there a set standard for this (ISO, FTA) to refer to or is this what has given you the most consistent results.
i only ask because i will need some way of backing this up as i move forward with this. also do we need to wet the tile before laying the the label on it like we would for opacity?
Thanks
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Re: how do you get delta E readings on clear film

Postby Frank Burgos » Wed Aug 27, 2014 10:31 am

No wahala.

ANSI CGATS.5:2009, which is the same as ISO 13655:2009
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Re: how do you get delta E readings on clear film

Postby Frank Burgos » Wed Aug 27, 2014 10:36 am

Sorry. Forgot the wet tile question.

The only time I've wet the backing, and it wasn't actually the backing, has been when printing on something that was going to be laminated. We'd spray a little water, perhaps having lowered the surface tension with a little soap, and fine-spray the solution over the laminate, then smooth down the printed layer over it, squeegeeing out bubbles. That assembly we'd place over the standard backing.
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