Great Image Quality--That Lasts
The industry has made tremendous progress over the last five years in the
performance of inkjet inks and media. There is now a host of wide-format printer
systems capable of delivering photographic-image quality and color, and many
specialty inks capable of achieving photographic lightfastness/fade resistance.
The dilemma, however, has been that in order to provide great color,
lightfastness had to be compromised – or vice versa.
Service providers have had to select inks for specific jobs based on the
application, and a trade-off had to be made between initial image quality and
durability over time. As a result, a different ink set may have to be loaded
into the printer to run a subsequent job, costing valuable production time and
labor – and wasting media and ink in the process.
An additional issue facing the industry has been agreement on a common way of
assessing product performance. Kodak has long advocated a complete view of
performance that includes ambient environmental effects such as temperature,
relative humidity, and airborne pollutants in addition to light fade data.
Although not a complete picture, we believe that in instances where light
intensity is a dominant factor to overall performance a limited "light-only"
view of product performance can be a useful reference point when making
A Single Solution
In the commercial segment, few end users need or see value in display prints
that last for tens or hundreds of years. In the midst of all the claims and
confusion about fade resistance and lightfastness, most professional /
commercial customers simply want to be sure that the materials they specify last
as long as possible without unnecessarily forcing trade-offs in color density,
cost or productivity. At Kodak Professional, we believe we have achieved the
solution – a single, affordable solution – to this dilemma.
Kodak Professional Enhanced Imaging Lightfast-Plus inks and media provide
a single solution that delivers both color equal to the best competitive inks
and industry leading lightfastness. These new inks and media effectively
eliminate need for constant ink changeovers and time-consuming printer
calibration. The service provider does not have to compromise one desired trait
for another, and now can achieve great image quality and color that lasts. Data
from our research indicate that Kodak Professional EI Lightfast-Plus inks
last two and a half times as long as the acknowledged leader for color fastness,
yet retains the highest image quality.
The Technology Behind the Performance
Traditionally, printer manufacturers have provided hardware-based
image-quality solutions that excelled in terms of color reproduction. Ink
companies experienced in dyes have principally focused on providing lightfast
solutions. But Kodak scientists, with their detailed understanding of color and
image science, have combined more than 70 years of experience in innovative
colorant technology with the knowledge gained over 100 years of making
As a result, Kodak Professional’s newest inks employ patented dyes that
provide great color and offer world-class performance in terms of
lightfastness/fade resistance. Kodak has invented more than 30,000 dyes just for
imaging over the years. We invent, develop, and manufacture these inkjet dyes
the same way we do the dyes for our world-class film products – with both
color and light stability in mind. Components are created and calibrated to
provide a complete system/solution, not merely a collection of products, to
provide the best available option for professional imaging labs and service
Color Gamut vs Lightfastness
As noted previously, until now, ink and paper combinations have been
optimized either for color reproduction or lightfastness. Traditionally,
manufacturers of inks with a high level of lightfastness have been required to
trade off superior color gamut. Therefore, it’s important to understand the
differences and interrelationship of these two attributes.
In achieving their results – Kodak Professional EI Lightfast-Plus
inks deliver both lightfastness and color gamut without compromise – Kodak
scientists made two critical breakthroughs in developing these new inks and
media. They also have been awarded patents (U.S. Patents 5,997,622 and
6,001,161) in recognition of their efforts. When used in combination with the Kodak
Professional 4700 series wide-format inkjet printers, these inks and media
provide a unique, top-performing combination of lightfastness and color gamut.
Measuring Color Gamut
Color gamut represents the breadth of colors and the number of discrete
colors that a particular combination of printer, ink, media, and RIP (Raster
Image Processor) can achieve. End users sometimes complain about "out of
gamut" errors. These occur when a given color is simply not available from
the selected "system." The RIP compensates by printing another color
that the system can achieve, but this substitute may have lower density
or the wrong hue.
Measuring color gamut is not simple, and expressing the results can be even
more challenging. Color gamut can be expressed in several different ways (Appendix
1). It can be measured in terms of two-dimensional a*b* color space
(as an area that represents the scope of gamut covered), or in three-dimensional
CIE L*a*b* space. Kodak created a proprietary three-dimensional measure in this
space,which uniquely factors in lightness as well as a* (green-magenta axis) and
b* (yellow-blue axis).
We are confident this three-dimensional approach defines gamut more
precisely, and we will refer to it in this presentation. But because of the
confidential nature of this proprietary methodology, we will express color gamut
in terms of the two-dimensional a*b* color space that is more familiar to most
readers. Although these two-dimensional plots can be misleading at times (in
that they ignore lightness), they offer a more simple expression of color gamut
and reflect how most people in the industry view and interpret it.
Color Gamut Comparisons
Examination of the color gamut comparison graph in Figure 1 clearly shows
that Kodak Professional EI Lightfast-Plus inks offer a larger gamut over
the leading competitor. In addition, the plots show these inks to have enhanced
reds, purples, and blues as indicated by the additional gamut areas in the lower
right-hand portion of the plots.
Figure 2 shows a comparison of the calculation of the total color gamut
three-dimensional volumes by the proprietary method mentioned above. This method
provides a single quantitative measure of color gamut, and shows that the Kodak
Professional EI Lightfast-Plus inks have a much larger color gamut than the
Although the results in Figure 2 appear to be more straightforward, they
should be looked at in conjunction with the two-dimensional graph, which better
illustrates specific areas of strength or weakness. A more complete
understanding of color gamut requires that these measures be used together to
characterize its overall scope and nuances.
Assessment of Lightfastness/Fade Resistance
For an inkjet print, the assessment of "print life" usually
involves a highly subjective process. The life of a print can depend on any
number of factors:
color density of the original image
determining whether the print is exposed to direct sunlight or daylight
duration of that exposure
use of a filtered or unfiltered light source
measuring the loss of print density or fading the customer expects and
In addition, the effects of humidity, heat, air pollution or other
environmental factors can also degrade the realized life of customer prints.
Given this variety of conditions and applications and the subjective nature of
individual assessments, it is extremely difficult for manufacturers, service
providers, and end users to uniformly estimate and assess print life. Yet this
is precisely what service providers must know to make sound business decisions.
Kodak research scientists and the Kodak Professional product team have worked
to identify a process for evaluating and measuring inkjet print performance in
the higher-intensity, large-format commercial display market. While not an
absolute measure of print life, this approach provides a controlled way to
document the relative performance of competing technologies. 1 Rather than varying
numerous variables in terms of duration of exposure, light energy values, and
direct/indirect exposure, we used a comparative approach that applies a standard
ANSI methodology (Appendix
2) and enables a controlled test of individual
combinations of inks and media.
While there are many contrived answers to the question of print life, we
advocate employing a fact-based, objective method to produce results so that a
fair comparison can be made. Given the controlled nature of the tests, results
can be compared directly across different manufacturers’ offerings. This
approach offers a useful tool to evaluate and select appropriate technologies
without the potential for confusion in terms of variations in exposure
conditions (direct/indirect), light energy values or duration to arrive at a
desired result. A direct comparison of performance provides a legitimate way for
fabricators to make informed choices both today and over time, and to offer the
best value to the end users of these products.
Estimating Print Life
Things start to get confusing when projections are made regarding print life.
It is critical to note that there is not yet an industry standard for
lightfastness/fade resistance testing. So many of the claims that end users
encounter in the trade media have been calculated using different failure
criteria, varying test lighting conditions, and individual assumptions about
lighting conditions for a specific application.
For example, most experts assume the common commercial display conditions in
a mall, store or other retail location to be 450 lux of light exposure, for 12
hours a day, under fluorescent light. 2 Rather than waiting for the results of
lightfastness testing in real-time, manufacturers have employed accelerated
testing to speed their learning. This approach is based on the assumption that
fading is a function of exposure (E), and that exposure is the product of
intensity (I) and duration (t).
E = I x t
By increasing the intensity of the light (I), testers are able to deliver
higher exposure levels in the same amount of time, thereby accelerating the
impact of exposure. The high-intensity bulbs typically used in most accelerated
tests, and the type used in our accelerated testing, produce 50,000 lux. To
further accelerate results, images were exposed to this level of intensity for
24 hours a day. If we make the assumption that the image fades reciprocally (see
below), one day in a high-intensity test chamber under these assumed display
conditions is equal to 222 days in real life.
50,000 lux/450 lux x 24 hours/12 hours = 222 days
Taking the number of days in the high-intensity test chamber until failure,
and converting them into years as calculated above, we find that the print made
with Kodak Professional EI Lightfast-Plus inks has an estimated print
life of at least 33 years. In comparison, the leading competitor lasts only 13
years. On the basis of this direct comparison, Kodak Professional EI
Lightfast-Plus inks and media outperformed the acknowledged industry leader for
lightfastness – lasting 2.5 times as long.
But what if the light intensity at the retail location is different? Suppose
the print is in a location where the light exposure is less, or the store simply
has lower intensity bulbs or covers on the lights? Some manufacturers have
assumed indoor display conditions with a light intensity as low as 200 lux in
their calculations of print life (called "Low-Intensity Commercial
Display"). What happens to the print life under these conditions? Our
calculation from above needs to change to account for the lower daily light
450 lux/200 lux x 33+ years = 75+ years
With this modification, we now find that inkjet prints using Kodak
Professional EI Lightfast-Plus inks have an estimated life of 75 years,
while the leading lightfast competitor lasts 29 years. Figure 3 below summarizes
these results graphically.
One final consideration is the use of filtered vs unfiltered light. The test
methodology we employed used unfiltered light, exposing the inks and media to
the maximum amount of light from the high-intensity source. Many other
predictors of print life test their prints using Plexiglas™-filtered light or
under glass, which can filter out some of the light, reducing exposure and
extending the predicted life of their prints by 2-3x. 3 Using such an approach, it
may be possible to derive durability claims of 150 to more than 200 years for
the Kodak Professional EI Lightfast-Plus inks and media tested.
75 Years of Unfiltered Light x Filtered Light Factor of
2-3x = 150 to 225 Years
So how many years do prints last? It all depends. As we’ve noted, the
variables it depends upon are highly subjective and extremely sensitive. Given
the leverage provided by the high-intensity test light, which may be greater
than 100x the actual environmental conditions, even modest changes in individual
variables or assumptions can greatly skew projected lifetime results. This
latitude can lead to performance claims that are at best confusing and at worst
misleading to end users.
The Effect of High-Intensity Accelerated Fading
An additional issue is the underlying assumption that the relationship of
light exposure and fading is reciprocal and, therefore, the results of
accelerated tests are easily projected to actual use conditions. If the print
reacts reciprocally, that means the amount of fade the print undergoes is
related only to the total amount of light that reaches its surface, and not to
the intensity of the light source or the duration of exposure. Deviation from
this behavior is called reciprocity failure in the literature. 4 If
reciprocity holds, then these accelerated tests will accurately predict the
print life. If not, then these tests can produce erroneous
results when converting the amount of fading to actual years.
In addition, in the lower-intensity extrapolations, there has been no
accounting for the effects of thermal degradation, which become increasingly
important, and could become more limiting than lightfastness as ambient
illumination intensity is reduced.
So claiming a print life in years is difficult and potentially misleading.
Estimated life statements are "all over the board." Manufacturers seem
able to justify these differences by pointing to "concrete" test
results without satisfactorily acknowledging the sensitivity of these
projections to the formulae they are using to calculate their estimates. (Appendix
A Case for Relative Comparison
An alternative approach to judging print life that avoids the issues of
converting accelerated data into print-life estimates in years is to simply
compare prints exposed to the same conditions. Such a controlled test provides a
direct, objective comparison of fade resistance. Because these results are not
factored in any way and a standard measure of density is used to assess
"failure," there is little or no room for subjectivity in the results.
Kodak Professional supports testing inkjet prints using test conditions that
most closely match the way customers actually display prints, and advocates
using failure criteria that are common in the industry. A leading independent
testing service 5 has evaluated Kodak Professional’s combination of
inks and glossy inkjet papers, following the guidelines set forth in ANSI/NAPM
IT9.9, 1996. We believe this is a method that will ultimately prevail, as it
provides a legitimate basis for industry-wide indoor light fade testing in the
higher intensity, large-format commercial market.
Using the same methodology, results of our "relative comparison"
testing include those of the leading competitor, long considered the benchmark
for lightfastness in inkjet prints. The failure criteria used standard measures
explained in Appendix
2. They were applied consistently to both samples and
include a combination of primary color and secondary color fade. Total exposure
was measured until a predetermined color-density end point was achieved. The
data supporting Figure 4 show the relative results of these tests: Kodak
Professional EI Lightfast-Plus inkjet prints last 2.5 times longer than the
leading competitor, the previous de facto standard for inkjet durability
– and delivered best-in-class color gamut as well.
We have reviewed various methods for measuring color gamut and
lightfastness, and have pointed out those methods we feel best provide
customers with a legitimate way to compare product performance.
This paper has demonstrated some of the ways in which it is possible to
derive print-life claims in excess of 100 years, essentially by adjusting test
conditions and environmental assumptions. Many of the values for assumptions
used to support claims in the trade press fall outside of expected values for
typical applications. Such examples include the use of filtered light, light
under glass or "low intensity" light sources of 200 lux. These
assumptions could misrepresent the actual performance of the product to end
Based on side-by-side controlled testing and direct comparisons, Kodak
Professional demonstrates first-in-class performance in terms of
lightfastness, and delivers color gamut that is at least equivalent to the
most colorful inks in the industry (inkjet prints produced on a Kodak
Professional 4700 series inkjet printer using EI Lightfast-Plus inks).
We have discussed in creating these products, how Kodak Professional has
leveraged Kodak’s proprietary knowledge and experience in image science to
the benefit of our customers.
We have demonstrated that Kodak Professional can save imaging labs and
service providers time and money – and most importantly deliver
best-in-class inkjet prints that will far exceed end user requirements for
image quality and durability.
Finally, we have established that there is no longer a need to trade off
color gamut for lightfastness. Imaging labs, service providers, and end users
no longer have to compromise if they use Kodak Professional Enhanced
Imaging Lightfast inks and media in a Kodak Professional 4700 Series
1 Kodak scientists continue to work on better methods of defining print life encompassing all of these variables, and we intend to work with industry bodies to standardize those definitions.
2 Consumer storage and display conditions could be dramatically different.
3 Bugner and Suminski, Proc. IS&Ts NIP 16, 2000; and Carmody, Evans, and Robinson, Proc. IS&Ts NIP 16, 2000.
4 James, The Theory of the Photographic Process, 4th Ed., p133.
5 Data from independent tests performed at the Image Permanence Institute at Rochester Institute of Technology.