The stationarity of a texture can be considered a fundamental property of images, although the property of stationarity is difficult to define precisely. We propose a stationarity test based on multiscale, locally stationary, 2D wavelets. Three separate experiments were performed to evaluate the capabilities and the limitations of this test. The experiments comprised a chessboard stationarity analysis, two classification tasks, and a psychophysical experiment. The classification tasks were performed on 110 texture images from a texture database. In one subtask, five texture feature vectors were extracted from each image and the classification accuracy of two classical methods compared, whereas in the second subtask, the classification accuracy of several methods was compared to the descriptors defined for each image within the database. In the psychophysical experiment, the correlation between the classification results and observer judgements of texture similarity were determined. It was found that a combination of wavelet shrinkage and rotation-invariant local binary pattern best predicted the observer response. The results show that the proposed stationarity test is able to provide relevant information for texture analysis.
KEYWORDS: Real time imaging, Visualization, Medical equipment, Contamination, Environmental sensing, Fluctuations and noise, Video, Cooling equipment, Microscopes, Navigation systems
To prevent contaminations and infections, various precautions are taken in an OR environment. Personnel wear masks and special clothing and a laminar flow of clean air is created within the sterile operating field. However, this controlled environment can easily be disturbed by the movements of personnel and medical equipment with internal cooling fans. In progress of a previous study, a special large field air flow visualization technique has been adapted to study and quantify the air flow around equipment used in the OR in real-time.
Optical distortions induced by small density gradients in flowing air can be visualized with high contrast and sensitivity in real time by subtraction of the fine line pattern in the background of the field of interest from the live video signal.
This technique was used to study the effectiveness of surgical masks, the disturbance of the laminar flow by the exhaust of cooling air from equipment like an operating microscope and surgical navigation system. Due to the real-time visualization, it is possible to focus on the region of interest and the instant effect of e.g. repositioning of equipment. Recording can be analyzed later to quantification.
Real time large field air flow imaging shows to be a sensitive and qualitative technique to study air flows. The awareness of the disturbance of the clean laminar air flow should lead to guidelines to improve the design and positioning of medical equipment in the OR to reduce infections.
ICC has announced a preliminary specification for iccMAX, a next-generation colour management system that expands
the existing ICC profile format and architecture to overcome the limitation of the fixed colorimetric Profile Connection
Space and support a much wider range of functionality. New features introduced in iccMAX include spectral processing,
material identification and visualization, BRDF, new data types, an improved gamut boundary descriptor and support for
arbitrary and programmable transforms. The iccMAX preliminary specification is accompanied by a reference
implementation, and will undergo a period of public review before being finalized.
A need for a baseline algorithm for mapping from the Perceptual Reference Medium Gamut to destination media in
ICC output profiles has been identified. Before such a baseline algorithm can be recommended, it requires careful
evaluation by the user community. A framework for encoding the gamut boundary and computing intersections with
the PRMG and output gamuts respectively is described. This framework provides a basis for comparing different
gamut mapping algorithms, and a candidate algorithm is also described.
A map is an information design object for which canonical colors for the most common elements are well established. For
a CVD observer, it may be difficult to discriminate between such elements - for example, it may be hard to distinguish a
red road from a green landscape on the basis of color alone. We address this problem through an adaptive color schema in
which the conspicuity of elements in a map to the individual user is maximized. This paper outlines a method to perform
adaptive color rendering of map information for users with color vision deficiencies. The palette selection method is based
on a pseudo-color palette generation technique which constrains colors to those which lie on the boundary of a reference
object color gamut. A user performs a color vision discrimination task, and based on the results of the test, a palette of
colors is selected using the pseudo-color palette generation method. This ensures that the perceived difference between
palette elements is high but which retains the canonical color of well-known elements as far as possible. We show examples
of color palettes computed for a selection of normal and CVD observers, together with maps rendered using these palettes.
KEYWORDS: Chemical vapor deposition, Cones, Visual process modeling, Color vision, Computer simulations, Visualization, Retina, Digital image processing, RGB color model, Absorption
A common task in universal design is to create a 'simulation' of the appearance of a colour image as it appears to a
CVD observer. Although such simulations are useful in illustrating the particular problems that a CVD observer has
in discriminating between colours in an image, it may not be reasonable to assume that such a simulation accurately
conveys the experience of the CVD observer to an observer with normal vision.
Two problems with this assumption are discussed here. First, it risks confusing appearance with sensation. A colour
appearance model can more or less accurately predict the change in appearance of a colour when it is viewed under
different conditions, but does not define the actual sensation. Such a sensation cannot be directly communicated but
merely located on a scale with other related sensations. In practice we avoid this epistemological problem by asking
observers to judge colour matches, relations and differences, none of which requires examination of the sensation
itself. Since we do not truly know what sensation a normal observer experiences, it seems unscientific to suppose
that we can do so for CVD observers.
Secondly, and following from the above, the relation between stimulus and corresponding sensation is established as
part of neural development during infancy, and while we can determine the stimulus we cannot readily determine
what sensation the stimulus is mapped to, or what the available range of sensations is for a given observer. It is
suggested that a similar range of sensations could be available to CVD observers as to normal observers.
KEYWORDS: RGB color model, Computer programming, Visualization, Brain, Color vision, Magnetic resonance imaging, Classification systems, Image classification, Tissues, Color imaging
Monochrome images are often converted to false-colour images, in which arbitrary colours are assigned to regions
of the image to aid recognition of features within the image. Criteria for selection of colour palettes vary according
to the application, but may include distinctiveness, extensibility, consistency, preference, meaningfulness and
universality. A method for defining a palette from colours on the surface of a reference gamut is described, which
ensures that all colours in the palette have the maximum chroma available for the given hue angle in the reference
gamut. The palette can be re-targeted to a reproduction medium as needed using colour management, and this
method ensures consistency between cross-media colour reproductions using the palette.
The perceived colour of a stimulus depends on the conditions under which it is viewed. For colours employed as an
important cue or identifier, such as signage and brand colours, colour reproduction tolerances are critically important.
Typically, such stimuli would be judged using a known level of illumination but, in the target environment, the level of
illumination used to view the samples may be entirely different. The effect of changes in the viewing condition on the
perceptibility and acceptability of small colour differences should be understood when such tolerances and associated
viewing conditions, are specified.
A series of psychophysical experiments was conducted to determine whether changes in illumination level significantly
alter acceptability and perceptibility thresholds of uniform colour stimuli. It was found that perceived colour
discrimination thresholds varied by up to 2.0 ΔE00. For the perceptual correlate of hue however, this value could be of
significance if the accepted error of colour difference was at the threshold, thereby yielding the possibility of rejection
with changes in illumination level. Lightness and chroma on the other hand, exhibited greater tolerance and were less
likely to be rejected with illuminance changes.
Paper Fluorescent Whitening Agent combined with differences in relative Ultra Violet levels between
instrument Illuminants, and real world viewing Illuminants, can be a significant source of error in characterising
a printing process, and hence in the ability to accurately reproduce coloured images in print and proof. The
appearance and measurement of fluorescent substrates depends strongly on the UV-amount in the source
illuminating a fluorescent sample which varies in the different viewing booths available.
The appearance of colours printed on substrates with optical brightening agents has been studied with help of a
colour matching experiment where the observers matched a colour patch displayed on a LCD monitor, by
adjusting its L*a*b* values, to another color patch printed out on paper viewed under varying amount of UV
content in lighting condition in the viewing booth. A customised viewing booth was built for this purpose and
substrates with varying amount of optical brightners were considered for the study.
A model based on CIECAM02 and a scaling technique has been developed to predict the perceived colour
match on a LCD display, of colours printed on substrates with optical brightners and viewed under the viewing
booth with varying amount of UV content in the viewing illumination. According to the obtained results, the
appearance of the colours printed on substrates containing optical brightners varied with variation in the amount
of UV content in the viewing illumination. The developed model gave good prediction of the XYZ tristimulus
values for the perceived match on the LCD display from the XYZ tristimulus values of the printed colours on
the substrate with acceptable ▵Eab . This shows that CIECAM02 can be effectively used for soft proofing.
Where an illumination source includes flux in the UV region, an estimate of the total flux in the UV can be derived from
the fluorescent efficacy of a reference material and the fluorescent emission from the material. A correlate of fluorescent
efficiency was derived using a triangular weighting function in the fluorescent emission region and the flux in the
fluorescent excitation region. This was found to be constant at different flux intensities, and was used to estimate the UV
content of a test illumination. The method gave good results but requires further verification using other materials and
illumination intensities.
In a late binding workflow, data is commonly prepared in an output-referred state based on a reference intermediate RGB
colour encoding. Such encodings may have a larger gamut than the target printing condition, and so there is some
ambiguity over how to preview the data before it has been converted to the target printing condition.
Here we propose an additional intermediate encoding, referred to as a 'virtual printer' which bridges the gap between
three-component reference RGB or PCS encodings, and reference CMYK printing conditions.
The virtual printer has a large colour gamut which represents a superset of most available print gamuts. It is defined here
in terms of the reflectance and colorimetric coordinates of the virtual colorants, and associated colour mixing model.
When used in a colour reproduction workflow, documents can be initially rendered to the printer-like gamut of the
virtual printer, and channel preferences (such as black generation) can be defined. Re-rendering to a reference printing
condition and associated colour gamut is deferred, thus supporting re-purposing of the document.
Metrics are proposed which allow the evaluation of the intrinsic smoothness of an output colour transform. One metric is based on taking the second derivative of the transform. The second method computes a series of smooth gradients and evaluates the differences between these gradients and the actual output values. A psychophysical experiment was performed to evaluate the proposed metrics, and both were found to be highly correlated with the observers' visual scale
values.
Printing with white ink plays an important role in many printing processes, but white is difficult to integrate into colour
management processes since conventional measurements are uncorrelated with the ink amount.
A control method for white ink is proposed in which white is printed and measured over black. The resulting
colorimetric densities can be modelled by polynomial regression, allowing accurate prediction of tonal value. The model
can readily be inverted to predict the colorant amount required to match a given colorimetric density, and hence is a
suitable method of measurement that can support process control and colour management.
KEYWORDS: Printing, Transform theory, Color management, Visualization, Data modeling, Calibration, Colorimetry, Standards development, Color imaging, Process control
A colour management strategy based on a reference printer and reference medium is described. Additional printers and
media are then defined in terms of this reference printer. This makes it possible to estimate new transforms for a given a
printer and media with no new measurements, even when there is no characterization data available for this combination
of printer and media. A simple method of estimating the new transform was implemented and evaluated, and it was
found to give good results when the target printing condition was similar in gamut and colorant primaries to the
reference printer. This approach can be extended by applying more complex empirical models.
Judgments of complex images differ from those of uniform color samples in several important respects. One such difference is that a complex image is formed of a large number of discrete color elements. Observer judgments are based not on assessment of each discrete element but of a much smaller number of salient features. The judgment process can be considered as the selection of such features followed by the judgment of particular quality attributes for these features. Modeling the judgment process thus requires a set of well-defined quality attributes together with a methodology for the selection of salient features and their relative importance. In this project, a method of selecting colors within an image was considered. A number of measurement locations within a complex image were selected, and the color of these locations was measured on a series of reproductions. The reproductions were judged by a panel of expert observers for their match to a proof, using a category scaling of several image quality attributes. By comparing the measured color differences with the visual judgments it was possible to determine which locations carried the greatest weight in the assessments. It was also possible to make a limited prediction of the visual judgments from the measurements.
Colour management systems need to be accurate and repeatable, particularly in graphic arts applications such as converting image data to proofing systems and to final print processes.
Modelling and computation errors were analyzed for a number of characterization data sets including single press sheet measurements and reference printing conditions based on SWOP and ISO 12647-3. Errors were calculated at double precision and compared with the AToB, BToA and round trip errors found in ICC profiles generated from the same data sets.
Data sets which are averaged from measurements of multiple press sheets consistently performed better than transforms built from single-sheet measurements. A significant part of the transform error lies in the limited precision of computation. BToA transform errors averaging 1 ΔE*ab appear to be a reasonable expectation for well-formed data sets. This needs to be placed in the context of errors arising from measurement uncertainty and the variation in colour reproduction systems, which are considerably larger.
The ability of gamut mapping algorithms to handle a wide range of relative gamut volumes was evaluated. Five gamut mapping algorithms were tested on reproduction media ranging from glossy, coated paper to newsprint. Original media were photographic transparency and print, and CRT.
The psychophysical results indicate that the performance of gamut mapping algorithms is not greatly dependent on gamut volume of either original or reproduction media. Those algorithms which apply a linear scaling of lightness between original and reproduction are more consistent in their performance across different image types and reproduction media. The methods which performed best tend to be those that give more emphasis to preserving lightness over chroma.
Printing images on coloured substrates is an interesting challenge, since observers are partially adapted to the colour of the substrate. Existing colour management methods are not appropriate for coloured papers, since they ignore this partial adaptation and also experience problems in compressing the coordinates of the original to the gamut that can be reproduced on the substrate.
In the first two experiments, it was found that the degree of adaptation to a background colour was not dependent on the lightness or chroma of the background, and could thus be modelled with a constant degree of adaptation.
In the second experiment, different methods of determining the coordinates to print on coloured substrates were compared. A method in which the coordinates for printing on white, adjusted by a partial adaptation model using a degree of adaptation of 0.66, gave better results than the other methods tested. The method works best on papers of low colour strength, since as the colour strength of the substrate increases, the available colour gamut is reduced and the performance of different methods becomes more similar.
Reproducing a transparency original on a hard copy print is a cross-media reproduction task, and for the two to match when viewed simultaneously the different viewing conditions for the two media must be taken into account. When CIECAM97s is used to predict the appearance of the transparency using the cut-sheet surround parameters, the impact of the viewing condition is over-predicted for this simultaneous viewing task.
New values for the c and Nc surround parameters were derived for simultaneous viewing, where both print and transparency conditions are defined by ISO 3664.
In a second phase, a background luminance factor Yb was calculated from the luminance of the image, border and background fields, assuming that the effect of the background decays exponentially with distance. New values for c and Nc were also calculated which assume that the transparency surround when viewed simultaneously with a print is a weighted combination of the surround conditions for the two media.
When evaluated in a psychophysical experiment, reproductions made according to the optimised surround parameters found in phase 1, and the modified surround and background parameters found in phase 2, were judged to give a better match in the appearance of the two media than the CIECAM97s parameters.
KEYWORDS: Visualization, Colorimetry, Graphic arts, Data modeling, Printing, Tolerancing, Visual process modeling, Color imaging, Process control, Optics manufacturing
Visually neutral colours on three different graphic arts substrates were chosen in a psychophysical experiment. Observers selected the most neutral patch from 49 patches of similar lightness, where the substrate was allowed to provide an adapting field.
The results showed that the colours seen as visually neutral tend to have CIELAB a*, b* coordinates of 0 at the black point and to approach the a*, b* coordinates of the substrate at higher lightnesses. The adaptation to the substrate could be considered complete for a white substrate, but incomplete in non-white substrates.
The results were modelled by transforming the achromatic axis in CIELAB by two methods - one by normalizing to the XYZ of the paper white, and the other by the chromatic adaptation transform CMCCAT2000. The best results were obtained when the adopted white point was taken as the substrate XYZ, with the chroma scaled by a factor of 0.6. Chroma scaling had more impact on the results for normalization than for CMCCAT2000.
Gamut mapping algorithms were tested in a transparency-to- newsprint workflow, using features derived from studies of empirical mappings in high-quality color reproductions. The experiment compared different methods of determining the achromatic convergence point in simulations lightness-chroma compression, and compared linear compression against a non- linear distance-weighted compression. Algorithms whose convergence points were dependent on the lightness and chroma of the cusp and of the color being mapping performed better than those with fixed convergence points. The models using non-linear compression were strongly preferred over one using linear compression.
KEYWORDS: Data modeling, Instrument modeling, CMYK color model, Associative arrays, RGB color model, Data conversion, Performance modeling, Reverse modeling, Solids, 3D metrology
A new target for defining media gamut boundaries is described. The use of measured gamut boundary data using provided by this target is capable of improving the accuracy of gamut boundary predictions in both device model and gamut mapping computations. The accuracy of existing methods of calculating gamut boundaries can be improved by use of an enlarged gamut boundary training set to derive the gamut boundary descriptor. An alternate, computationally simple, method of calculating gamut boundary intersections is described, and its performance in calculating such intersections and in media mapping is described. There is good agreement between this method and FSLGB in predicting boundary intersections if the same data is used to derive the gamut boundary descriptor. The gamut boundary target described in this paper is thus proposed as a means of obtaining greater information about media gamut boundaries.
Color difference acceptability judgments in the graphic arts were investigated using 26 observers and 7 color centers with approximately 20 samples in each color center. In comparison with (Delta) Eab, CIE94 color difference (Delta) E94 was found to reduce the relatively high acceptability thresholds found in high-chroma yellows. It only partially corrected the low significance that (Delta) Eab gives to greys.
KEYWORDS: Networks, Graphic arts, Databases, Visualization, Telecommunications, Java, Printing, Data communications, Information assurance, Software development
The graphic arts industry is increasingly reliant on telecommunications for the transfer of digital data for media production. There are, however, many other aspects of the business process between customers and supplies that are suited to network-based interaction. The transaction between customer and producer can be separated into four data streams; briefing, content creation and production, and approval. Each of these data streams has specific requirements which lead to a matrix of needs for the different parties in the transaction. Proposals were made for meeting these needs through a network service dedicated to the graphic arts. British Telecom and Scitex are currently offering a service based on these proposals, known as Vio. A network service of this kind can be extended to include a range of other services and third-party interactions, such as automated transfer of media production objects from third-party content providers. The opportunities for users and third-party developers to develop a custom network applications and interfaces between the network and internal production processes and monitoring systems using open IP-based methods are described.
The graphic arts industry is increasingly reliant on telecommunications for the transfer of digital data for media production. There are, however, many other aspects of the business process between customers and suppliers that are suited to network-based interaction. The transaction between customer and producer can be separated into four data streams: briefing, content creation and production, and approval. Each of these data streams has specific requirements which lead to a matrix of needs for the different parties in the transaction. These needs are reviewed and proposals made for meeting them through a network service dedicated to the graphic arts. British Telecom, MCI and Scitex are currently beta-testing a service based on these proposals, known as the Digital Graphic Network. Once a managed network service is in place, it is possible to extend it to include a range of other services and third-party interactions, such as automated transfer of media production objects such as high-resolution images, fonts, color profiles, etc. from third-party content providers. The opportunities for users and third-party developers to develop a custom interface between the network and internal production processes and monitoring systems using open systems based on the Java language is described.
This paper describes the issues associated with digital files and high-end color reproduction. It highlights some industry experiences related to the use of digital files and considers what the Adobe AcrobatTM PDF format may contribute to meeting the needs of high-end color reproduction. The purpose of the project was to determine whether the PDF 1.2 format is capable of achieving the high-end color requirements of today's pre-press industry. The methods used to test the PDF 1.2 format are described, and the results discussed. For all the features tested it was found that the results were equivalent to using PostScript, and the suitability of the format for high-end color reproduction was confirmed.
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