Halftone Dots Research Articles

604 オプティカルドットゲインの影響を排除した網点抽出アルゴリズムの構築(潤滑・情報・知能)

604 オプティカルドットゲインの影響を排除した網点抽出アルゴリズムの構築(潤滑・情報・知能)

Experimental Results on Human Visual Sensitivity for Spatial Frequency of Digital Halftone Images

In this paper we add some new experimental results to our recent work and discuss them with respect to human visual sensitivity for spatial frequency. In our experiment, several dot pattern images and sinusoidal gratings are used to probe the capabilities of the visual system.We can see some characteristics of human perceptual system when we analyze our experimental results from the viewpoint of halftone dot size, shape and frequency.

Suppression of Automoiré in Multi-Level Supercell Halftone Screen Designs

An optimization approach is proposed for suppressing the automoiré, also known as internal moiré, in multi-level periodic screen designs. This artifact can appear when the halftone dots of a rational tangent screen do not have integer offsets in pixels. Starting with an ideal continuous space halftone pattern for a given level, a bounded, constrained convex optimization problem is solved to obtain the best discrete space halftone pattern values on the pixels of the supercell tile. The optimization minimizes a least-squares spatial frequency weighted difference between the pattern when first reconstructed to continuous space by the printing system (e.g. exposure) and the ideal pattern. The resulting halftone pattern has been found to typically contain very little energy outside of the screen's fundamental frequencies and harmonics while preserving the original ideal dot shape reasonably well. A series of such patterns so derived can be converted to multi-level threshold arrays if the pattern values are quantized and the stacking constraint is enforced during optimization.

A Novel Hybrid Amplitude Modulated/Frequency Modulated Halftoning Based on Multilevel Halftoning

A digital gray scale image generally consists of 256 different gray tones. Printers and image setters normally generate much fewer levels and mostly only two levels. Therefore, in order to be able to display a digital cone-tone image by a multilevel device it has to be transformed into an image with fewer levels. The technique doing this transformation is called multi-level halftoning, and in the case of bilevel devices it is simply called halftoning. In this paper we propose a novel (bilevel) halftoning technique that is based on multilevel halftoning. The proposed method can also be categorized as belonging to hybrid amplitude modulated (AM)/ frequency modulated (FM) techniques. In this method the original digital image is firstly halftoned by a multilevel FM halftoning. Each level in the multilevel halftoned image is then replaced by a halftone table (microcell). An approach for extending any bilevel FM halftoning method to a multilevel method is also presented in this paper. The performance of the proposed method is examined by a number of illustrations where nonmodified error diffusion and our FM method are used. The problem with maze-like artifacts that occur when our FM halftoning, or similar methods such as DBS, are used as the macroscreen is discussed and a simple solution is introduced. An approach for extending the proposed method to be used in situations where the halftone dots cannot be produced smaller than a specific size is also proposed and examined. This modified version of the method can be useful for flexography where the dots normally cannot be produced smaller than a critical size.

Contour perception of half-toned density step image

Contour is important elements of image and is usually expressed by the density jump between two areas of image. Recognition of object is usually carried out from the contour. In some cases, emerging of false contour is problem in image coding and de-cording process. Half-toning is essential processing for digital printing of continuous tone. Contour perception conditions are studied experimentally on various half-toning conditions, observation distances, and illumination conditions. It is found that the contour perception become easy as the stimulus of the halftone dot decreases in human visual system.

Gravitational Re-allocation of Halftone Dots for Moiré-Free Color Proofing

Gravitational Re-allocation of Halftone Dots for Moiré-Free Color Proofing

Some Characteristics on Human Visual Sensitivity for Spatial Frequency of Digital Halftone Images

In this paper we show some experimental results of image recognition, and discuss them from the viewpoint of human visual sensitivity for spatial frequency. We have been interested in how we see digital halftone images which consists of halftone dots.

Low-complexity comprehensive labeling and enhancement algorithm for compound documents

We present a multiresolutional algorithm that segments a compound document and uses the results of the segmentation for document enhancement in copier applications. The document is initially segmented into halftone and nonhalftone areas. Based on this segmentation the location of the edges due to text, graphics, and images (and not due to halftone dots) are detected on halftone as well as on nonhalftone portions. We further detect constant-tone regions within nonhalftone areas for subsequent bleed-through removal applications. Edge enhancement on detected edges and descreening on detected halftones are carried out. The algorithm can detect general halftones over regions of arbitrary sizes and shapes, and it can be straightforwardly adjusted for operation at various dpi resolutions. We obtain high detection probabilities on compound multilingual documents containing halftones and fine text. The proposed enhancement stage is tolerant of segmentation errors providing robust performance for the remaining problem cases. Our main contribution is the accomplishment of these tasks with a single pass algorithm that is computationally very simple and that requires less than 1% of full page memory, with active memory requirements less than 0.02% of full page memory. The operation of the algorithm can be imagined as a very thin line (of thickness the size of a full-stop in 11 pt text) that rapidly scans an input page while simultaneously producing an output page.

A Study on High Efficiency Image Coding for Binary Images with Halftone Dots Using Vector Representation

A Study on High Efficiency Image Coding for Binary Images with Halftone Dots Using Vector Representation

Empirically Based Printer Model of Halftone Structure

A number of image quality metrics depend on the structure of the printed halftone dot. The dot structure depends in a complex way on the individual processes in a xerographic marking engine. This paper describes a model which reduces this complexity into a set of key parameters. The parameters are derived from microscopic optical measurements of the dot structure in the halftoned print on paper. The halftone printer model is written specifically for a single color separation, fast calculation, and physically based parameters. Given a fill pattern and a threshold value, it calculates the local image density as a function of position in a halftone supercell. The model has been applied to the appearance of partial pixels and to high frequency banding caused by irregularities in the raster optical scanner (ROS) beam spacing.

Separation model of colour regions in a halftone print

To evaluate print characteristics on the basis of scanned microsamples of printing sheets, it is necessary to carry out the segmentation of particular colour regions, printed with process inks. The accuracy of the evaluation of print characteristics strongly depends on the successful segmentation of the colour regions involved in a print sample. The first step of segmentation must be the separation of the specific colour from a multicolour sample. This paper describes the method of colour separation based on the evaluation of differences between the colours involved in the print sample. The result of the separation process is a monochromatic image, which is further processed by segmentation methods to gain accurate regions of specific colour or regions of halftone dots.

Application of Ink Jet Printer Model to Evaluate the Sharpness of Printed Images

Image sharpness is an important factor for image quality evaluation. This paper investigates the effect of dot misregistration to the sharpness of ink jet image on various type of papers. The printed one-pixel line images are simulated using the proposed ink jet printer model. The model simulates each digital halftone dot in a high resolution grid using ink spread function and optical point spread function of paper. The variables in the experiment are the degree of dot misregistration and optical point spread function of paper. Fourier analysis is applied to those simulated images and the sharpness parameter is evaluated and compared. The results show that when dot misregistration is about 1/3 of dot diameter off its intent location, the MTF at 6 cy/mm is lower than 0.5 therefore poor sharpness is observed.

An investigation into screen printing using UV process colour inks

This paper presents the results from a comprehensive exploration of printing sequence based on dot gain, colour gamut and grey balance characteristics for screen printing. The tests involved designing a test image and this included the successful incorporation of a novel feature to explore grey balance. This allowed the three process colours, cyan, magenta and yellow, to be varied independently. The results confirmed the excellent repeatability of the process when printing a conventional UV ink. The results also showed the small impact of increasing the ink base up to 30% on tone gain and the colour range was not affected by the printing sequence. The results showed that print sequence had a major effect on the grey balance, and this was traced to the effect of a gasket on the stencil, and that half-tone dots from the first print effectively generated a rough surface that affects the gasket formed by the stencil. The results show that tonal reproduction and colour range measurements are not appropriate quality indicators. For precision screen printing, quality measurement should be made on the image, and that separation and screen preparation needs to account for process settings and the printing sequence used.

Does the Halftone Print Still Need a Photographic Quality?

Many patented screening techniques were brought to the market during the last decade as a challenge to the conventional ones. The “photographic quality” prevailed in their advertised advantages to indicate on a higher definition of prints thereby produced. However, for example, in FM and error diffusion screening the increase of spatial resolution is accompanied by the structural non-uniformity and loss of tone rendition. Lower printability has to be compensated by reduction the NSR of a printing system, i.e. by the use of a finer, hence costly, consumables and plate-ink-paper interaction. That resulted in poor practical implementation of these techniques in spite of their availability in the prepress software and equipment of the most vendors.To the contrary, resolution and sharpness are improved in the Adaptive Screening technology with no effect on the printability of a halftone structure. For the stationary image area it stays exactly the same as in a widely used conventional methods. At the same time, the halftone dots or the parts thereof no more exist at contour and fine detail and don't destroy the latter. As our experimental printing shows, the effect of an improvement is different for various kinds of jobs and printing conditions. So, this effect is to be discussed with taking into account:- the sampling factor (SF);- screen ruling value;- dot pattern geometry for the stationary image area.

The Fundamentals of HP Indigo's Digital Offset Color Printing Process and How It Rivals Mechanical Offset Printing

In recent print shows, the Indigo Division of HP has introduced new presses based on the new BID development system, the fastest digital color printing products in the industry and with photographic quality capabilities for the high end photo market. “Digital Offset Color” is a process combining HP's unique electrically-responsive ink, “ElectroInk”, with a specially-developed thermal transfer process and a fast color switching technique. These are complemented by an ultra-high performance multi-beam laser scanner and unique image processing software. Pumping through the heart of HP's Indigo digital press is its propriety ElectroInk. ElectroInk enables these liquid electrophotographic printing presses to deliver prints of true offset quality. Only one to two microns in size, charged ElectroInk particles form highly defined characters, line work and halftone dot patterns. The “look and feel” of offset is achieved by a combination of ElectroInk's high saturation and extended color gamut and its unique ability to replicate the surface gloss of the underlying paper stock. The very small particles form extremely thin ink layers, less than one micron thick, enabling both high quality and low cost. Latent image formation, Binary Ink Development, and thermal offset transfer are discussed.

Hidden images in halftone pictures

A method of concealing an image in a different halftone image is proposed. Continuous-tone levels of the visible images are represented by the area of the halftone dots. However, the hidden image is encoded by the dots' positions inside their cells. Only a spatial correlator with a unique filter function can reveal the hidden image from the halftone picture. The technique and its robustness to noise and distortions are demonstrated.

Reducing Multi-Separation Color Moiré by a Variable Undercolor Removal and Gray Component Replacement Strategy

One common artifact in color printing is the moiré caused by the superposition of the different color separations. This problem is well known and a common approach to minimize the moiré is the use of rotated halftone dots of precise frequency and angle for the different separations. In low resolution devices, the precise relationship between the different separations is commonly hard to satisfy and compromises have to be made. This paper describes a method to vary the undercolor removal (UCR) and gray component replacement (GCR) schemes employed as a function of the predicted inter-separation moiré in order to allow for a better trade-off in the halftone design.

Irrational Halftoning for Electronic Registration

As xerography moves to intercept offset printing, image quality becomes a key ingredient of success. Classic halftoning methods, which generally deliver good, low noise halftone dots, have fixed positions in the scan field that hinder several possible improvements to these printing systems.First, exact halftone frequencies and angles would result if dot positions could be adjusted with arbitrary precision. This would improve the design of screen-sets that limit or reduce multiseparation moiré, or allow screen-sets that exhibit the classic rosette structure associated with offset printing.Second, electronic registration systems could emerge if the halftone dot positions could be adjusted in response to actuation commands from the printer. Such systems would automatically compensate for mechanical distortions caused by bent mirrors, elliptical rollers, and tandem color print stations, for instance, and thus save manufacturing costs for the mechanical system.Normally, the dot positions are fixed to small integer offsets (the angle corresponds to a “rational tangent”) in the scan field, thus preventing the occurrence of single separation moiré. When fractional dot positions are allowed (irrational tangent), moiré can result. Thus, if the moiré problem can be eliminated for irrational halftoning, the frequency and angle restrictions associated with rational tangent halftoning disappear.I will present one solution to this problem that subsamples a halftone cluster function stored in a look-up table to produce reduced moiré separations while printing. Halftone dot locations are computed by hardware, and dot cluster shapes typically do not repeat. I will show a simulation of a three-separation image printed on a 600 spi digital printer that uses irrational offsets (m30°, c75°, and k45°) designed to produce a classic rosette structure. I will also show a simulation of these same dots being electronically registered, or warped.

Extracting color halftones from printed documents using texture analysis

Printed documents often contain text and halftones on the same page. When processing these documents electronically, it is important to separate halftones from text and other illustrations, since their processing requirements differ. We present an algorithm that extracts both grayscale and color halftones from other information on a page. Halftones are commonly produced as a pattern of dots on a uniform lattice. The halftone dot pattern forms an “invisible texture”, producing a spectral component distinct from other information on the page. We show that a single circularly symmetric bandpass filter, tuned to this spectral component, can be used to segment halftones having arbitrary shape and size, even in the presence of image rotations.

The Near Ultraviolet and Infrared Light Dye-Sensitized Systems and Application to The Photoimaging.

Diphenyliodonium hexafluorophosphate can be sensitized efficiently by the dyes Michael Ketone and NK-2204 and produced H+ which can catalyzed the crossing reaction of the HMMA resin and the m-cresol resin. Therefore, the system composed of Diphenyl iodonium, sensitizer, Michael Ketone or NK-2204, and the HMMA resin and the m-cresol resin can be used in the photoimaging study. The effects of the molar ration of the HMMA resin and the m-cresol resin, the heated temperature and times on the resolution and the halftone dot repetition of the printing plate were carried out.