RE: Dot Gain
RE: Dot Gain
- Subject: RE: Dot Gain
- From: Ray Maxwell <email@hidden>
- Date: Wed, 30 Apr 2003 10:29:12 -0700
Peter Wrote:
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From: Peter Baumbach
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Sent: Wednesday, April 30, 2003 6:29 AM
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To: email@hidden
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Subject: Re: Dot Gain
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I thought that the "optical" dot gain is something "only" perceived by the
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visual system. Look at the so called Herman grid
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(http://www.michaelbach.de/ot/lum_scgrid/index.html). The white area
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between
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the black dots is perceived as gray which would explain that the perceived
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dot gain is larger than the measured dot gain. So I would say that a
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densitometer just measures the amount of light which is reflected or
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transmitted by the paper or film, in other words the "mechanical" dot gain
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due to the actual distribution of ink on the paper or silver in the film.
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The "N-factor" would then serve as a correction factor for the "optical"
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dot
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gain and the logarithmic behaviour of the visual system when lightness is
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involved.
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Am I missing something?
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Regards,
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Peter Baumbach
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Hi Peter,
I am enclosing a quote from ANSI CGATS.4.1993 "Graphic technology--Graphic
arts reflection densitometry measurements--Terminology, equations, image
elements and procedures". This can be purchased from the NPES web site at
"
http://www.npes.org";
3.14 dot area (%), apparent: the dot area of a printed halftone element
which is computed from the reflection densities of the printed element and
areas of solid, continuous coverage. The computation of apparent dot area
makes use of the Murray-Davies equation (see Section 4.3.1). It accounts
for the physical area covered by the dot pattern plus optical effects which
cause the dots to appear larger in size (optical gain). This approximates
the visual impression of the printed area.
4.3.2 Yule-Nielson (Y-N) equation: a modification of the Murray-Davies
equation used to estimate the physical dot area. An empirically determined
factor "n" is included to calculate an approximation of physical dot area
resulting from the use of specific raw materials (ink, paper, substrate,
etc.) used in the printing process. This "n" factor must be determined for
each set of raw materials.
Usually the Yule-Nielson measurements are used when measuring plates. Since
you are interested in the physical size of the dot on plate rather than it's
appearance. On press sheets and proofs you use Murry-Davies since you are
interested in an "approximation" of the appearance.
I would encourage everyone to get the NPES catalog and purchase many of the
standards documents that are available. This would go along way in
standardizing the industry's understanding of the terminology that is used.
Hope this helps,
Ray
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Creo
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Ray Maxwell | Senior Color Systems Engineer, Inkjet Printing
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4225 Kincaid Street | Phone (604) 451-2700 ext. 2004
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Burnaby, B.C.
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Canada V5G 4P5
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IMAGINE CREATE BELIEVE
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