Iarigai kolseth lanat savborg printing by-the-numbers stockholm 2009 paper

1. Printing by the numbers on commercial paper grades
Petter Kolseth, Luc Lanat, Örjan Sävborg
Stora Enso, SE-79180 Falun, Sweden. petter.i.kolseth@storaenso.com
Luc Lanat: Stora Enso, Mönchengladbach Research Centre, Krefelder Strasse 560, DE-41066
Mönchengladbach, Germany. luc.lanat@storaenso.com
Örjan Sävborg: Stora Enso, Karlstad Research Centre, P.O. Box 9090, SE-65009 Karlstad, Sweden
orjan.savborg@storaenso.com
Abstract
Printing standards have been around for many decades, but the detailed ISO standardisation evolved only a
little more than ten years ago. The graphic standard series ISO 12647 Graphic technology – Process control
for the production of halftone colour separations, proof and production prints is making an ever stronger
impact on the graphic industry. This has, unfortunately, created unnecessary confusion. Especially there are
some details in Part 2: Offset lithographic processes that sometimes result in a clash between supplier, printer
and print buyer. The limitation to a few specific paper types with characteristics that hardly match
commercial paper grades, and the not always realistic targets for printed colour and tonal transfer giving rise
to sometimes endless debate. The present work describes some of the measures that have been taken by us as
a paper supplier to alleviate the situation. As a general conclusion, we may state that a majority of
commercially available papers could be confined in rather narrow groups with respect to shade, attainable
printed colour and tone value increase, provided that the right parameters are chosen.
–1–
Keywords
COLOR MANAGEMENT; LITHOGRAPHIC OFFSET; PAPER CHARACTERISATION; PAPER OPTICS
1. Introduction
Standardised Print – or Printing by the Numbers – has evolved from a buzz to something that is
demanded from many printers today. Standardised Print is not as straightforward as it may seem. What
we today refer to as Standardised Print has a long background history. The German graphic research
institute FOGRA and the German Printers and Media Association bvdm presented their first guidelines in
the early 80’s. The Swedish merchant Pappersgruppen (now Papyrus) were early adopters in Sweden with
seminars for the printers. In 1993, Michael Haas at FOGRA invited representatives of mainly pre-press
companies to a meeting in München. This was the starting point of the ICC – International Color
Consortium. They agreed upon a specification of a standard file format for the description of colour, and
how the conversion between different colour spaces should be handled using ICC profiles. It has however
always been up to the different colour software suppliers to use these specifications in building their
proprietary colour management systems.
Colour management is all about transforming colour information from one device to another, typically
from an input such as a digital RGB-coded colour image to an offset press printing the four process
colours Cyan-Magenta-Yellow-Black (CMYK). There are still many unresolved issue in how colour
management should be best implemented, and the ICC colour management system is still evolving as
understanding increases. We will not go into any details in the field of colour management in the present
work; the interested reader can find pertinent information in the many white papers issued by the ICC
(www.icc.org).
From the German printers in particular, there has since some years now been a request for the
papermakers to specify key properties of all papers related to colour management and print process
control in a uniform way. One important issue is the colour appearance and tone rendering achieved when
putting ink on paper in the printing press. There is obviously a need for some standardisation of output
colour, and for this purpose, the first parts of the graphic standard series ISO 12647 Graphic technology –
Process control for the production of halftone colour separations, proof and production prints were
released in 1996. The ISO 12647 standard covers not only lithographic offset (sheetfed and heatset), but
also coldset offset, gravure, screen and flexography print. “Digital” printing is not included, but there is
one part dealing with contract proofs. The common debate has been primarily focused on the offset
lithography, partly because it was the first to appear, and maybe also because it is the most common
process by number of practitioners. The newspaper associations have since long worked according to
well-accepted de facto standards, so there has been rather limited debate. The work presented here deals

2. only with offset lithography, but we will most certainly find reason to follow up on rotogravure, which
today is being pushed by large print buyers such as IKEA.
The ISO 12647 parts 1-3 are presently under systematic revision, a progress report being presented by a
working group at the recent TC130 meeting in Fort Worth 19-21 May. The aim is obviously to get out of
the notion of “ISO compliant papers”, and rather base paper categorization on achievable colours in solid
and halftone print. The working group has not really abandoned paper categorization, presenting four
categories: coated and uncoated, of high grammage and low grammage. Each of these four categories is
still linked to paper shade, achievable ink coloration and specific TVI (Dot Gain) curves. This approach
seems anyway constructive, but there are still many obstacles to overcome, including fluorescence
effects. With the recent strong engagement from paper industry in the TC130 processes, there is good
hope that graphic and paper industries may come to a mutual understanding on the content of these
standards.
The objectives of our present work have been to clarify some of the more common issues in the current
debate. Particularly, we have studied the effect of paper shade and paper fluorescence, achievable colour
coordinates of the CMY-RGB hexagon, and the contribution of paper to the tone value increase (TVI/dot
gain). Standardization and UV calibration of light sources, choice of proof to print papers, repeatability of
equipments have also a major influence on printing quality control. We therefore studied and evaluated
the importance of these elements on our road to “Printing by the numbers”.
2. Results and Discussion
Paper shade
The ISO 12647 standard did not evoke any significant discussion between printer and papermaker during
its first years of existence. The paper shade issue was one of the first questions to reach our sales force,
and that did not happen until the years 2004-05, more than eight years after the standard was published.
The standardisation of paper shade is certainly not very clear though. The exact wording in the ISO
standard is as follows:
Print substrate colour The print substrate used for proofing should be identical to that of the production. If
this is not possible, the properties of the print substrate should be a close match to that of the production in
terms of colour, gloss, type of surface (coated, uncoated, super-calendered, etc.) and mass per area. Press
proofing should be carried out on the closest match selected from five typical paper surface types whose
attributes are listed in Table 1. For off-press proofing the print substrate should be selected to conform as
closely as possible to the attributes listed in Table 1 of the paper type representing the envisaged production
paper. The type of paper shall be stated.
Table 1. CIELAB coordinates and gloss for typical paper types according to ISO 12647-2
Paper type L* a* b* gloss
1. Gloss-coated, woodfree 93(95) 0(0) -3(-2) 65
2. Matte-coated, woodfree 92(94) 0(0) -3(-2) 38
3. Gloss-coated, web 87(92) -1(0) 3(5) 55
4. Uncoated, white 92(95) 0(0) -3(-2) 6
5. Uncoated, slightly yellowish 88(90) 0(0) 6(9) 6
Tolerance ±3 ±2 ±2 ±5
D50 illuminant, 2° observer, 0/45 or 45/0 geometry, black backing (values in brackets refer to white backing).
This is obviously related to the print substrates used for proofing? It is stated that both shade and gloss are
normative, but is this for the proof substrate or the production paper? Clearly, the (mis-)interpretation so
far is that the standard is a categorisation of paper in five “allowed” types, and that it is possible to
become a certified printer only if you print on a production paper that fits into one of these categories.
The real problem is now that the prescribed CIELAB coordinates do not comply with what is common for
today’s commercial paper grades. The discrepancy is mainly related to the b* coordinate, most paper
having a stronger bluish shade making them look whiter. This whiteness is partly due to the addition of
fluorescent whitening agents (FWA, also called OBA – optical brightening agents). The paper types
chosen in writing the standard may have been “typical” then – long before 1996 – but are far from typical
today.
–2–

3. In order to explain the situation to our sales force and our customers, we analysed a large set of gloss-coated
(Paper Type 1) and silk/matt-coated (Paper Type 2) offset papers from the European market in
2005. Figure 1 shows that all products except for one wood-containing product were out of range when
colour was determined the paper industry way with D65/10° settings.
–3–
0
-1
-2
-3
-4
-5
-6
-7
-8
-9
-10
-5 -4 -3 -2 -1 0 1 2 3 4 5
CIELAB-a*
CIELAB-b*
0
-1
-2
-3
-4
-5
-6
-7
-8
-9
-10
-5 -4 -3 -2 -1 0 1 2 3 4 5
CIELAB-a*
CIELAB-b*
Figure 1. Paper shade in D65/10° for 51 coated papers of 90-250 g/m2.
Left: Paper Type 1; Right Paper Type 2
Making the measurements in C/2° conditions move some papers, mainly wood-containing, into the
prescribed tolerances, left part of Figure 2. Measurements with a graphic industry instrument
(Spectrolino) in D50/2° allowed most glossy products to fit inside the tolerances, right part of Figure 2. It
is however clear that the “natural” range of commercial products is wider than the given ISO standard
tolerances.
0
-1
-2
-3
-4
-5
-6
-7
-8
-9
-10
-5 -4 -3 -2 -1 0 1 2 3 4 5
CIELAB-a*
CIELAB-b*
1
0
-1
-2
-3
-4
-5
-6
-7
-8
-9
-5 -4 -3 -2 -1 0 1 2 3 4 5
CIELAB-a*
CIELAB-b*
Figure 2. Paper shade in C/2° (Elrepho – Left) and D50/2° (Spectrolino – Right) for the gloss-coated
papers (PT 1) in Figure 1.
In June 2006, there was a joint ICC, ISO TC130 (graphic) and ISO TC6 (paper) meeting to address Paper
Categorization, where representatives from both graphic industry and paper industry met for the first time
to discuss these matters. The meeting agreed to set up a working group with Uwe Bertholdt of FOGRA as
coordinator, asking the group to come up with recommendations for changes to the existing standards and
any new standards which are required. FOGRA measured about 500 papers from around the world, and
the data definitely showed that papers intended for offset printing were significantly bluer than indicated
in the ISO 12647-2. FOGRA came however to the conclusion that even though changing the prescribed
paper shades in the standard would result in a more valid paper description of real papers, this would

4. result in an increased visual mismatch between proof and print because most (all?) digital proof systems
simulate the fluorescent blue shift of printing papers by using blue dye instead of fluorescent agents. The
results were presented at the ISO TC130 meting in Bangkok in April 2007, and later in September 2007 at
the Print Media Production Forum in Stuttgart.
–4–
0,00
-1,00
-2,00
-3,00
-4,00
-5,00
-6,00
-7,00
-8,00
-9,00
0,00 0,50 1,00 1,50 2,00 2,50
CIELAB-a*
CIELAB-b*
Figure 3. Shades of double-coated glossy papers determined by FOGRA for the ISO TC130 paper
characterization working group. A relatively small change of the allowed a*-b* range would allow more
than 80% of the samples to fit inside these tolerances.
CIELAB coordinates of colours for four-colour printing
The ISO 12647-2 also specifies the CIELAB colour coordinates of the process colour solids (CMY) and
the two-colour overprints (RGB).
Figure 4 shows the achieved colour on the same papers as shown in Figure 1. The press settings were the
same for all papers, using the same target densities for process control. The resulting CMY and RGB
colour coordinates were found in a rather narrow range for all 51 papers. The wider range of Yellow in
the b* direction was due to silk-coated papers only, and was not related to bluish paper shade.
100
80
60
40
20
b*
-a* a*
0
-100 -80 -60 -40 -20 0 20 40 60 80 100
-20
-40
-60
-80
-100
-b*
Figure 4. Colour gamuts (D50/2° Spectrolino) of
51 gloss and silk-coated papers and target values
given in ISO 12647-2.
100
80
60
40
20
CIE -a* CIE a*
-100 -80 -60 -40 -20 20 40 60 80 100
-20
-40
-60
-80
-100
CIE b*
CIE -b*
Figure 5. Colour gamuts (C/2° Elrepho) of ten
different inks on gloss ‘, silk U and matt …
coated fine paper.
We have also tested ten different inks from six ink suppliers. One supplier was asked to select five
different types of inks, which were combined with standard inks from the other five suppliers. Figure 5

5. shows the achieved colour on three coated papers: gloss, silk and matt. The press settings were the same
for all 30 combinations, using the same target densities for process control. The resulting CMY and RGB
colour coordinates were again found in a rather narrow range. The main difference between the inks was
a wide range of print gloss levels: print gloss in 100% black was in the range of 45-55% on matt, 58-72%
on silk and 78-92% on gloss.
It is clear that most – if not all – papers of the same basic type are able to reach the same CMY-RGB
colour targets. Once the CMY colour targets have been achieved, the RGB colours are fixed. Even after
the 2004 amendment to the ISO 12647-2, these colours do not usually coincide with the targets of the
standard. Surprisingly, the recent FOGRA characterization data fit these targets to the second decimal.
The data have obviously been smoothed and shifted to comply with the ISO standard and may therefore,
be of limited value to the press operator.
Fluorescence effects
The high Whiteness levels of paper are mainly achieved via fluorescence, Figure 6. A more bluish shade
is perceived as more white according to research by the CIE that resulted in the CIE Whiteness equation.
Therefore, we can expect that fluorescence continues to be a significant paper property also for many
years to come, and it has to be accounted for in colour management.
Elrepho D50/2°
–5–
70
60
50
40
30
20
10
100 110 120 130 140 150
CIE Whiteness (D65/10°)
Fluorescence (D65/10°)
Figure 6. Fluorescent component of coated fine papers in a wide range of whiteness levels.
Products in the range of 200-350 g/m2 from Europe, USA and China.
The colour coordinates of printed tonal steps in CMY-RGB were determined with different illuminant-observer
combinations. Figure 7 shows the D65/10° and D50/2° colour on a silk-coated fine paper. The
upward shift at the origin reflects the lower relative UV content in D50. As a result of the more red D50
illuminant and the stronger colour vision of the 2° observer, this combination shows more colour
saturation, especially in the red region.
Elrepho D65/10°
100
80
60
40
20
0
-20
-40
-60
-80 -60 -40 -20 0 20 40 60 80
a*
b*
100
80
60
40
20
0
-20
-40
-60
-80 -60 -40 -20 0 20 40 60 80
a*
b*
Figure 7. Colour coordinates in tonal steps of CMY-RGB on silk-coated fine paper.

6. In order to see the effect of fluorescence, the D50 readings were made also with a UV-cut filter, Figure 8.
–6–
20
10
0
-10
-20
-30
-40
-50
-60
-60 -50 -40 -30 -20 -10 0 10 20
a*
b*
D50 D50UVex
Cyan
60
50
40
30
20
10
0
-10
-20
0 10 20 30 40 50 60 70 80
a*
b*
D50 D50UVex
Red
40
30
20
10
0
-10
-20
-30
-40
0 10 20 30 40 50 60 70 80
a*
b*
D50 D50UVex
Magenta
40
30
20
10
0
-10
-20
-30
-40
-60 -50 -40 -30 -20 -10 0 10 20
a*
b*
D50 D50UVex
Green
100
80
60
40
20
0
-20
-60 -40 -20 0 20 40 60
a*
b*
D50 D50UVex
Yellow
20
10
0
-10
-20
-30
-40
-50
-60
-40 -30 -20 -10 0 10 20 30 40
a*
b*
D50 D50UVex
Blue
Figure 8. The effect of a UV-cut filter on printed colour coordinates on silk-coated fine paper.
The CMY primaries were clearly shifted towards higher b* over the entire tonal range. The secondaries
were less affected due to a higher UV screening power. The only point that did not show a shift on UV-cut
was solid Green, all other data points moved slightly. Similar data were reported in a diploma work by
Katharina Kehren (2008). She also provided a mathematical model for predicting the effect of different
fluorescence levels.
Paper fluorescence is seen through almost any ink coverage used in commercial printing; only solid
Green (100C + 100Y) was not affected by fluorescence effects. The contribution of fluorescence is of
course dependent on the relative UV content in the measuring instrument. Paper industry and graphic
industry standards differ in this respect. A draft revision of the ISO 13655 standard includes the
measurement condition M1, which should give results close to a true Illuminant D50. The calibration of

7. relative UV content is however still not clearly addressed a fact that may lead to poor match between
production paper and proofing substrates. Papermakers needed and therefore developed fully operational
calibration procedures (and standards), valid for illuminants D65, C or D50 (at UV level of C illuminant).
The corresponding shifts on a highly fluorescent uncoated fine paper were of course larger, and
consequently, there were no shifts on a non-fluorescent substrate, Figure 9.
OBA-free yellowish uncoated
Relative to 440 nm fluorescence peak
–7–
20
15
10
5
0
-5
-10
-15
-20
-20 -15 -10 -5 0 5 10 15 20
a*
b*
D50 i1D50 D65
Uncoated fine paper
20
15
10
5
0
-5
-10
-15
-20
-20 -15 -10 -5 0 5 10 15 20
a*
b*
D50 i1D50 D65
Figure 9. Paper white colour coordinates determined with Elrepho D65/10° and D50/2° and with the
iOne D50/2° of highly fluorescent and non-fluorescent uncoated paper.
The exact measurement conditions for spectral measurements in graphic and paper industry standards are
under development and debate. The paper industry standard conditions for measurement of CIELAB
coordinates of paper and print is described in ISO 5631, where detailed instructions are given for
adjusting the relative UV content. Part 1 is for D65/10° and Part 2 for C/2° settings. A draft version of
Part 3 describes D50/2° settings with the same UV adjustment as for the illuminant C. This choice may
have seemed practical for the ISO working group, but unfortunately, the relative power of D50 is more
than twice that of C between 340 and 380 nm. Figure 10 shows the spectral power relative to 440 nm,
which is the wavelength where we see the fluorescence peak of all our tested papers (coated and
uncoated).
Absolute power
300
250
200
150
100
50
0
350 400 450 500 550 600 650 700 750
Wavelength, nm
Spectral Power
D65 C D50 A
2,00
1,75
1,50
1,25
1,00
0,75
0,50
0,25
0,00
340 360 380 400 420 440 460 480 500 520 540 560
Wavelength, nm
Spectral Power
D65rel Crel D50rel Arel
Figure 10. Absolute and Relative UV content of the four Illuminants D65, C, D50 and A.
In the draft revision of ISO 13655, four measurement conditions are described: M0 (no filter = Illuminant
A), M1 (true D50), M2 (UV-cut filter) and M3 (polarization filter). The M1 condition should be possible
to achieve with a Tungsten lamp as used in standard graphic spectrometers by applying a filter working in
the visual region that would increase the relative UV content to the D50 level.

8. The match between measurement conditions and the actual spectral power distribution in viewing booths
remains to be addressed. A true D50 viewing booth is probably nowhere to be seen, and the lighting
conditions at the end user are totally unknown.
Tone Value Increase (Dot Gain)
The transformation of tone value from digital file to the final print on paper plays an important role in the
control of the printing process. Earlier, this was often referred to as Dot Gain (Tone Value Increase),
since the perceived tone in print was always higher than the tone value on the film that was used to make
the printing plates. From the papermaker’s point of view, the Tone Value Increase (TVI) from the imaged
printing plate to the final print is the main interest; the paper can have no effect on the earlier pre-press
stages. It is sometimes suggested that the TVI should be an inherent paper property, a misconception that
fortunately is generally disputed by specialists within the field of printing and graphic arts.
The TVI behaviour of the same set of coated papers as in the sections on paper shade and printed colour
was analysed in detail. The TVI curves obtained with standard densitometry are shown in Figure 11.
–8–
TVI Black
30%
25%
20%
15%
10%
5%
0%
0% 20% 40% 60% 80% 100%
Nominal tone
Tone Value Increase
TVI Cyan
30%
25%
20%
15%
10%
5%
0%
0% 20% 40% 60% 80% 100%
Nominal tone
Tone Value Increase
Figure 11. TVI curves for Black and Cyan of 51 gloss and silk-coated papers. Almost all curves fall inside
the allowed range 14% ±4% TVI for the 50% control patch.
A subset of 40% black halftone (K40) prints over the TVI range was selected for a detailed microscopy
analysis. The extremes are shown in Figure 12, where it is clear that the higher TVI was related to severe
doubling or slur.
Figure 12. Nominal 40% Black halftone prints of 13,2% TVI (left) and 20,1% TVI (right).
Figure 13 shows histograms of the reflectance values of the two prints. Two characteristics can be seen in
the diagrams: the white peak between-the-dots is both wider and darker in the high-TVI print. This is
mainly related to the poor dot quality, but the also the paper white seems to be a bit darker. The darker
paper between dots is commonly referred to as “optical dot gain” as described by Yule and Nielsen
(1951). The effect was recently reviewed in a conference paper by Smith et al. (2009).

9. 100 (1)
–9–
2,5
2,0
1,5
1,0
0,5
0,0
25,0
20,0
15,0
10,0
5,0
Halftone dots Between dots
Solid black
Unimaged
paper
0 20 40 60 80 100
Reflectance, %
Frequency, %
0,0
<K40> <BLACK> <WHITE>
2,5
2,0
1,5
1,0
0,5
0,0
25,0
20,0
15,0
10,0
5,0
Halftone dots
Solid black
Between
dots
Unimaged
0 20 40 60 80 100
Reflectance, %
Frequency, %
0,0
<K40> <BLACK> <WHITE>
paper
Figure 13. Reflectance histograms of the microscopy images in Figure 12 together with histograms of
solid black and unimaged paper.
A simple analysis was based on the reflectance histograms. The position of the four peaks (solid black,
halftone dots, paper between dots, unimaged paper) and the average reflectance under the three curves
were determined.
The edge of the physical dots was defined by setting a threshold at the mean reflectance between the
peak of halftone dots and the peak of paper between dots in the K40 histograms. The corresponding tone
values are denoted “Physical” in Table 2.
The K40 Tone Values given in Table 2 were calculated from the average reflectance values of the Black
halftone, solid Black and unimaged paper:
K40
K100
ToneValue R
K40 R −
R
= ×
0
The Optical Tone Value Increase was calculated as the difference by the Tone Value and the Physical
Dot as seen in microscopy.
The “brightest area between dots” was estimated as the average reflectance of the 15% of the region
between dots that was far away as possible from the dots.
Table 2. Tone values of nominal 40% Black halftones as seen by densitometer and by microscopy
Paper ---- Densitometer ---- --------------- Microscopy ---------------
TVI-40 DensTone Physical ToneValue Optical TVI
Multicoated silk 250 13,2 53,2 42,0 47,2 5,2
Multicoated silk 115 13,4 53,4 41,6 47,7 6,1
Multicoated silk 250 15,1 55,1 42,5 48,2 5,7
Single-coated matt 90 15,5 55,5 41,9 50,4 8,5
Multicoated gloss 115 16,3 56,3 42,7 48,6 5,9
Multicoated gloss 250 16,9 56,9 44,6 50,2 5,6
Single-coated matt 90 19,3 59,3 47,4 54,7 7,3
Multicoated gloss 250 20,1 60,1 44,0 51,4 7,4
Compared to the target of 40%, the physical dot sizes of 41,6-47,4 displayed in Table 2, indicate a
mechanical TVI in the range of 1-8%. The exact determination of printed dot size is fraught with error,
mainly because of uncertainties in setting an exact threshold for the extension of the dots. The low-end of
1,5-2% mechanical TVI was found for the most perfect dots, but a minute change in thresholding would
bring the mechanical TVI down to zero. The large mechanical TVI values were clearly related to less than
perfect dots that displayed both doubling and slur. The analysis of the microscopy images gave a
disappointing underestimation of the Tone Values by approximately 6%, Figure 14. The reason for this
was not fully understood by the authors at the time of this report.

10. –10–
56
54
52
50
48
46
50 52 54 56 58 60 62 64
Densitometer Tone Value
Microscopy Tone Value
Figure 14. Comparison of Tone Values determined by microscopy and densitometer.
Table 2 also shows that an optical TVI in the range of 5-9% was found in the analysis of microscope
images. This optical TVI was closely related to the reduction in paper reflectance between the dots as
compared to the unimaged paper, Figure 15. Please note that the reduction in paper reflectance is highest
for single-coated matt and lowest for multicoated silk, with multicoated gloss in between. This follows
the expected visibility of the high-lateral light-scattering power of the base sheet through the coating. The
results infer that optical TVI may be an inherent paper property, with a contribution to the total TVI seen
by densitometry that is at least in the range of 5-10% TVI for the paper Types 1 and 2.
10,0
8,0
6,0
4,0
2,0
0,0
-20 -15 -10 -5 0
Reduction in paper reflectance between dots
Optical TVI
Single-coat matt
multicoat
gloss multicoat silk
Figure 15. The optical TVI as a function of the shift in paper reflectance from “unimaged paper” to
“brightest between dots”.
3. Conclusions
The paper shade, especially if it is affected by blue fluorescence, may introduce problems in matching to
proofs, but such problems should be possible to handle by a well-working colour management system.
There seem to be two main reasons for the sometimes poor match between proof and print regarding
paper shade.
First, the proofing substrates generally have less fluorescence than the corresponding commercial paper.
Some colour management software seems to compensate for this by printing a light blue shade on the
white substrate, which of course, does not provide fluorescence. The opposite may also be true, with
highly fluorescent proof substrates, Figure 16. An (obviously) ideal solution would be to choose a proof
substrate approaching the fluorescence level of the production paper. A New Working Item (NWI) will be
proposed to ISO TC130 to this end. The shade of commercially available paper grades fall in general
within a rather tight range. This range is offset mainly in the negative b*-direction from the ISO 12647-2
standard paper types, but the limits could quite easily be adjusted to comply with real papers. This was
concluded in an investigation by FOGRA already two years ago, but for some reason it was decided not
to make this rather obvious change.
Secondly, the offset inks provide a stronger blocking of UV rays than the inkjet inks used for proof prints.
The fluorescence contribution should therefore be treated differently in proof printing and production

11. printing. In a diploma work initiated by our company, it has been shown that the fluorescence effect in
real prints can be described by a quite straightforward model over the whole CMY-RGB tonal range.
–11–
6,0
4,0
2,0
0,0
-2,0
-4,0
-6,0
-8,0
-10,0
-12,0
-14,0
-2,0 -1,5 -1,0 -0,5 0,0 0,5 1,0 1,5 2,0 2,5 3,0
CIELAB-a*
CIELAB-b*
Paper Type 2
Paper Type 4
Figure 16. CIELAB shades of proof substrates (circles) and production paper (squares). The red symbols
denote FOGRA certified proof substrates.
The intrinsic Tone Value Increase (TVI or “dot gain”) of the paper is clearly related to the Yule-Nielsen
effect – the optical TVI. On a “perfect” print, the physical dot coverage was found to be very small or
almost zero, coinciding with the values on the printing plate, so mechanical TVI may not explain the high
tone values values measured with a densitometer. The grey shadow between dots may fully explain what
the densitometer “sees” as higher dot coverage. This basic level seems rather to coincide with the norms
presented by for example FOGRA and bvdm. Excess “dot gain” would have to be attributed to pre-press
settings from digital file to plate, or to non-ideal printing conditions with doubling or slur.
The debate is presently about calibration procedures, where paper industry is promoting the advanced
calibration systems used for their spectrophotometers, and the possible mismatch between relative UV
content in D50 as defined by paper industry and graphic industry. Paper industry representatives also
encourage the addition of D65 as a fifth measurement condition in the ISO 13655, hence called M4.
ISO 13655 version 2 is still judged to be misleading, until proper calibration procedures, in particular in
the UV level of the light source, have been added. As an example of the wide variety of instruments in
use, the reader is referred to the PIA/GATF report by Radencic et al. (2008).
The situation has improved considerably over the last years, since paper industry is now engaged in the
development of printing standardization. This contributes to the success of printed media obviously. This
is the common goal of all of us, printers, papermakers, suppliers to the graphic industry and, we believe,
publishers. As an example, this work was widely reviewed and discussed within the “Paperdam”
technical working group, gathering experts from Burgo, Norske, UPM, Myllykoski, Stora Enso and
Sappi/M-real, on Colour Management and Standardization issues.
Printed Media is highly needed for human communication and Quality Print Media will support its
development. Print Media Quality – “We know it when we see it”.
4. Measurement Methods
We have used a wide arsenal of techniques, from full-scale printing trials in sheetfed offset and heatset
web offset, to detailed optical analyses of paper and print. The prints were analysed both with standard
instruments from the graphic industry and with the special equipment used in the paper industry.
Optical properties All paper optical properties were obtained with an L&W Elrepho 3000 instrument,
calibrated using ISO Level 3 reference papers from STFI (now Innventia). The CIELAB coordinates of
paper and print were determined both with D65/10° and C/2° settings according to ISO 5631. L*a*b*-
coordinates were also evaluated with D50/2° settings according to a draft version of ISO 5631.
Spectrodensitometry Two instruments were used: a Gretag Spectrolino and an X-Rite iOne, both with
“No filter” option and thus in essence an Illuminant A. The CIELAB coordinates were calculated with the

12. D50/2° arithmetic, but the relative UV content was still corresponding to illuminant A, which is slightly
higher than true D50.
Densitometry Print density was determined using a Tobias scanning densitometer without polarizing
filters, calibrated according to DIN Status E(47B). The output from the instrument is about 0,1 density
unit lower than normal European densitometer readings (e.g. Gretag) in the CMY process colours, and 0,3
units lower in Black.
Microscopy Images (micrographs) were recorded by a digital camera NIKON DXM1200 mounted on a
LEICA MZ12 stereomicroscope. The images were saved as “BW”. Illumination was from two light
sources mounted at about 45° on either side of the sample.
When the images were inspected with Adobe Photoshop CS3 it was discovered that the “BW” tiff format
was of the type “Indexed color” and to remove this they were saved as “grey”.
The physical size of the halftone dots was measured using a simple Visual Basic program. The two
maxima in the histogram corresponding to ink and unprinted paper were determined and the image
thresholded at the midpoint between these maxima. All dark objects that are not in contact with the image
border and that have an area greater than 200 pixels were measured.
The “brightest area between dots” was evaluated from the segmented images of dots and background
(between dots) as described above. A distance transform was calculated where each pixel in the
background was given the value of its shortest distance to the foreground (dot). The maximum in the
distance transform is simply the pixel furthest away from its surrounding dots. The distance transform
was thresholded at 75%, 80%, 85% and 90% of the maximum in order to get small regions as far away as
possible from the surrounding dots, and the average brightness of these pixels was determined. The
average showed a slight increase with the threshold (less than 1 unit between the highest and lowest
threshold) and the value at 85%, rounded to a whole number was chosen as “brightest between dots”.
The 255 grey levels were transformed into reflectance by matching the paper white peak level with the
Y-value of the papers.
Printing plates Kodak Electra Excel positive thermal plates were imaged on a Creo Lotem 400 Quantum
CTP plate setter, using SQUAREspot exposure technology. The screening used was Euclidean dot (round
dot shape at 40% tone), 175 lpi. The plate setter was calibrated to give a linear tonal transfer curve (zero
dot gain).
Printing trials Printing trials were performed on a Heidelberg Speed-Master 6-colour sheet-fed offset
press. The CPC system was used to print at target densities of K 1,90 – C 1,50 – M 1,50 – Y 1,40. The
printing was made with a vegetable oil based ink from Akzo Nobel Inks, using an 8% IPA fount system.
The ink transfer to the paper was optimised using compressive blankets with a microground surface and a
relatively high blanket-to-paper impression at 0,18 mm. The printed papers were gloss- and matt/silk-coated
papers for sheetfed offset, covering a grammage range of 90-250 g/m2.
5. Acknowledgements
We want to acknowledge valuable contributions by many colleagues, among those we want to especially
mention Anna Nicander, Sofia Thorman (ex Norstedt), Stefan Eriksson and Olle Henningsson.
6. References
Print
Kehren, K. (2008), Einfluß optischer Aufheller auf die Druckbildwiedergabe, Diplomarbeit TU Darmstadt.
Radencic, Greg; Neumann, Eric; Bohan, Mark (2008), Spectrophotometer Inter-Instrument Agreement on Standard
Reference Materials and Printed Samples, PIA/GATF Catalog No. 1646.
Smith, D. A.; Williams, D. M.; Salminen, P. J.; Welsch, G. W.; Heeschen, W. A.; Nicholas, N. R.; Arney, J. S.
(2009), Definition and Model for Primary Grey Scale Mottle as a Variation in the Yule-Nielsen Effect in Offset
Printed Coated Paper, TAPPI PaperCon ’09, St. Louis, USA.
Yule, J. A. C.; Nielsen, W. J (1951), The penetration of light into paper and its effect on halftone reproduction,
TAGA Proceedings 3:65-76.
Internet
Print Media Production Forum 2007 (bvdm/ECI): http://www.print-media-production-forum.de/eng/index.php
FOGRA Characterization data: http://www.color.org/FOGRA.xalter
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13. CV’s of the authors
Petter Kolseth is Expert Science & Communication within Stora Enso PrintNet. He is presently focusing
on the development of media in general and printed media in particular. He worked for almost a quarter
of a century at the Swedish Pulp and Paper Research Institute (STFI, now Innventia), before he joined
Stora Enso in 1996. At the STFI, he took the long journey from single wood pulp fibres and wood
polymers, to the printed paper surface. At Stora Enso he started in Printing & Graphic Arts of fine paper,
and has gradually widened the scope to all printing papers.
Luc Lanat is Expert Science & Market within Stora Enso PrintNet at the Mönchengladbach Research
Centre, Germany. He deals with Product Performance Magazine paper. He started at Centre Technique du
Papier Grenoble, then served Fasson Division of Avery-Dennisson in The Netherlands and Belgium as
Technical Sales Support Manager, then Papeteries de Condat in France as Quality Manager. He integrated
Stora Enso Corbehem mill in France in 1996, as Production Manager and Process and Quality Manager
until 2005 where he joined Magazine Paper Business Area.
Örjan Sävborg is Senior Specialist Microscopy within Stora Enso Publication Paper R&D. He has a PhD
in inorganic chemistry from the Stockholm University and joined Stora Enso in 1985 after a post-doc
period at Arizona State University. He has a background in trouble shooting work but also in the use of
image analysis methods for evaluation of print quality and sheet structure characterization.
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