Artifex
Imaging Science Technologies
EvenArtifex
is pleased to offer outstanding imaging science
technologies in the areas of screening and color
management. Please download our datasheet for more
information:
Imaging
Science datasheet
Screening
Artifex
offers two high-performance screening technologies,
Well Tempered Screening (WTS) and Even Toned Screening
(ETS).
Even
Toned Screening
Even
Toned Screening controls undesirable halftone patterns
and textures, a form of error diffusion screening
optimized for inkjet printers, using a technique
known as Output-Dependent Feedback Screening.
Error
diffusion is a technique for breaking a continuous
tone image into a dot structure suitable for ink-on-paper
printing. Error diffusion produces a very finely
dispersed dot structure, which is particularly well
suited to inkjet printers. Most other printing technologies,
including laser and offset printing have difficulty
reproducing such fine structure.
The
earliest error diffusion algorithm was invented
by Floyd and Steinberg in 1975, and is still considered
one of the best. However, many error diffusion algorithms
produce visually noticeable artifacts as a result
of the dot placement choices. Techniques to reduce
these artifacts are an active area of research.
Exceptional
features of error diffusion screening include total
freedom from moire, as well as unparalleled fidelity
in reproducing fine detail. These features have
helped ensure error diffusion's dominant role in
halftoning for inkjet printers.
Overall
quality
Producing
high quality output with any screening technique
requires custom-tuned color profiling targeted for
that screen. The smooth response of ETS makes it
more convenient to make a superior color profile,
and therefore an overall superior quality output.
This
high quality screening technique adds output-dependent
feedback to the conventional error diffusion halftone,
improving these halftones significantly.
with
Even Toned Screening - - - with Floyd-Steinberg
``Wormy''
Textures in Highlights and Shadows
Error
diffusion halftones are plagued by a ``wormy'' texture
in highlights and shadows. This undesirable effect
is caused by limitations in the logic used by error
diffusion to place dots. With Even Toned Screening,
the visual texture of highlight and shadow tones
are made more uniform, eliminating the wormy textures
that can occur with conventional error diffusion
halftones.
This
screening technique is effectively identical to
placing each halftone dot in the center of a circle
and packing the circles tightly together. The resulting
texture appears very homogeneous, and is visually
pleasing to the eye.
While
Even Toned Screening can be applied to both highlight
and shadow dots, on inkjet printers only the highlights
cause visually noticeable patterns, because of the
ink spread. Thus, applying the output dependent
feedback to highlight textures only can speed processing.
``Tearing''
Adjacent to High-Contrast Areas
With
the smooth highlight areas created with Even Toned
Screening, ``tearing'' is also avoided. Tearing
refers to a screening artifact where the halftone
dots drop out next to high-contrast areas, creating
a hole or "tear" in the halftone image.
This
``tearing'' effect is particularly severe for mixed
pages containing images and line art or colored
text. The use of Even Toned Screening ensures excellent
results for all types of source images.
Availability
Even
Toned Screening is available in two forms. First,
it is a complete error diffusion algorithm using
a tuned version of Floyd-Steinberg to achieve excellent
smoothness for all tone values. Second, it is available
as a modification to existing error diffusion algorithms,
placing the highlight (and optionally shadow) dots
more smoothly while leaving the midtones unchanged.
The second option is desirable when work has already
been done tuning an error diffusion algorithm to
a particular device.
The
final result is a halftone with exceptionally smooth
highlight regions, free of "worming" and "tearing,"
with modest computational cost. The speed of Even
Toned Screening is within a factor of two of simple
error diffusion techniques such as basic Floyd-Steinberg,
the earliest and most well-known error diffusion
technique.
ETS
"Green Screen"
Green
Screen is a second-order FM screening that uses
variable dot placement and noise. This not only
eliminates moiré, but also improves the reproduction
of flesh tones. In addition Green Screen gives excellent
rendition of fine detail and produces smooth tints
and vignettes with no noise.
-
Exceptional reproduction of fine detail
- Smooth
multi-color vignettes with no noise
- No
visible dot structure in skin tones
- Increased
color gamut gives greater visual impact and wider
range of process colors
- Screened
type is sharp and legible
- Flat
tints are smooth
First-order
Stochastic Screening
First-order
stochastic screening uses fixed spot sizes, and
adjusts their frequency and proximity as needed
for midtones, highlights, and shadows. Also known
as FM (frequency modulated) screening, it prevents
moire and rosette patterns and allows textiles,
metal products, flesh-tones, and complex images
to render with amazing detail and clarity.
Second-order
Stochastic Screening
A
less desirable trait of first-order FM screening
is graininess. Green Screen corrects this deficiency
by using a fixed spot size only in the highlights
and shadows while allowing the midtones to vary
slightly. Green Screen produces visual density by
increasing both the size and frequency of spots,
enabling better tonal control and smoother, more
natural reproduction.
Unlike
other stochastic technologies, Green Screen does
not use tiles for dot placement, which can cause
repetition artifacts. Instead, Green Screen uses
error diffusion placement. Additionally, advanced
algorithms virtually eliminate the worm-like patterns
inherent to diffusion screening. The implementation
of Green Screen is in standard C, with additional
SSE2 (Pentium 4) optimizations to achieve blazing
performance on modern platforms.
Argyll
Color Management SystemTM
Argyll
is an ICC compatible color management system. It
supports accurate ICC profile creation for scanners,
RGB or CMYK printers, film recorders and display
monitors. Spectral sample data is supported, allowing
a selection of illuminants observer types, and paper
fluorescent whitener additive compensation. Profiles
can also incorporate source specific gamut mappings
for perceptual and saturation intents. Gamut mapping
and profile linking uses the CIECAM02 appearance
model, a unique gamut mapping algorithm, and a wide
selection of rendering intents. It also includes
code for the fastest portable 8 bit raster color
conversion engine available anywhere, as well as
support for fast, fully accurate 16 bit conversion.
Device color gamuts can also be viewed and compared
using a VRML viewer. Argyll also includes a general
purpose ICC profile format access library, icclib,
and a general purpose CGATS file format I/O library.
One
of the most compelling aspects of the Argyll Color
Management System is that we provide full source
code. This allows users in mission-critical projects
to tune and customize color handling to meet their
specific needs. This is one of the reasons that
Argyll was chosen as the color management system
for the DreamWorks animated movie "Shrek 2".
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Awards
In
partnership with RIPit, Even Toned Screening won
the 2003 "PDF Shootout" at Seybold San Francisco
for best quality PDF output, besting far more expensive
solutions.
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Publications
Levien,
R. ``Output Dependent Feedback in Error Diffusion
Halftoning'', IS&T 46th Annual Conference, Cambridge,
Massachusetts, May 1993. (also reprinted in ``Recent
progress in digital halftoning'', Reiner Eschbach,
ed., IS&T, 1995)
Levien,
R. ``Method and apparatus for error diffusion screening
of images with improved smoothness in highlight
and shadow regions'', US Patent 5,917,614, June
29, 1999.
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Obtaining
the freely available versions:
An
evaluation version of Even Toned Screening is
available under the Gnu GPL license for free download:
ets-1.1.tar.gz
- To
obtain the latest freely-available version of
Ghostscript PostScript and PDF, please download
from the following URL: http://www.cs.wisc.edu/~ghost/
To
obtain the latest freely-available version of
GhostPCL and Ghostprinter, please download from
the following URL: http://www.artifex.com/downloads/
