Re: ISO 12647-3 measurement (IT8.74 or ECI 2002) Lab data list---black backing and white backing
Re: ISO 12647-3 measurement (IT8.74 or ECI 2002) Lab data list---black backing and white backing
- Subject: Re: ISO 12647-3 measurement (IT8.74 or ECI 2002) Lab data list---black backing and white backing
- From: Graeme Gill <email@hidden>
- Date: Thu, 13 Jul 2006 14:37:45 +1000
Roger Breton wrote:
How, then, could you compare thin paper stocks among themselves, on color?
If measured on a black backing, they could appear (some #5 coated grades I
know) very neutral, with a* and b* close to zero. On the other hand, if
measured on a white backing, like the Spectroscan table, the same paper
shows a negative b* value, typically around -3, again for some papers I'm
familiar with. As a consequence, I can hardly tell unequivocally what is the
"color" of a thin paper stock. Lately, before loosing my mental sanity, I
started measuring over "nothing": I place the paper one inch away off the
surface of my desk so there is no backing behind it, just the space between
the top of my desk and the floor, about 30" or so. Then I measure, with my
SpectroEye, holding the paper from underneath between my fingers. It works.
But it's not an ISO standard :(
The procedure we'd use for such situations is to put several layers
of the paper under the instrument table. You can't know for
sure what backing the actual viewer will use when looking at
the final product, but often final products are books, magazines
or newspapers, where the backing will be lots of the same paper
(albeit with unknown printing on it that will sometimes show
through).
If your aim is to use instrument measurement to determine
what the final viewer sees, then you need to set the instrument
up as close as possible to how the viewer will be setup,
and ideally that includes the backing and the illuminant.
As I understand it, a black backing is intended for making
readings that you will compare numerically, and where the
sample may be printed on the back. So if you want to
check consistency of the output of a press, then black
backing will help. A profile made from such readings isn't
going to represent what the user usually sees very well though.
Theoretically your "measure over nothing" should be the same
as measuring over black - the light passing out of the back of
the paper isn't coming back.
Graeme Gill.
_______________________________________________
Do not post admin requests to the list. They will be ignored.
Colorsync-users mailing list (email@hidden)
Help/Unsubscribe/Update your Subscription:
This email sent to email@hidden