The Tug function: A Method of context sensitive dot structuring for digital halftones

The process of digitizing images to create halftones inherently reduces sharpness through the averaging of grayness values within cell areas. Within the context of a resolution independent page description language, overcoming this reduced sharpness is conventionally addressed by adjusting the grayness values of cells to create larger or smaller halftone dots where edges are present. Such an approach does not take full advantage of the capabilities of the output device. The objective of this project was to design and implement a method of sharpening digital images by altering the shape and position, rather than the size, of halftone dots. Such a method can more accurately represent the original image and more closely emulate the characteristics of photomechanically produced halftones. Within the PostScript page description language, the generation of halftone dots is controlled by the spot function. A particular type of spot function, the Tug function, was developed to control the shape and position of halftone dots based on the grayness value of each cell and its surrounding neighbors. Because the standard PostScript imaging operators are not designed to allow halftone dot shapes to be redefined on a cell-by-cell basis, an alternate method of generating images was created. A computer program in the PostScript programming language was written to perform the requisite image analysis and halftone dot structuring to drive a laser printing device for viewing the effects of the Tug function. Three representative photographic images were processed in this manner. A panel of judges compared the resulting prints with control prints processed without the Tug function but by the same imaging method. The judges\u27 subjective preferences are presented, and the relative merits of the Tug function are discussed

Pushing the Limits of 3D Color Printing: Error Diffusion with Translucent Materials

Accurate color reproduction is important in many applications of 3D printing, from design prototypes to 3D color copies or portraits. Although full color is available via other technologies, multi-jet printers have greater potential for graphical 3D printing, in terms of reproducing complex appearance properties. However, to date these printers cannot produce full color, and doing so poses substantial technical challenges, from the shear amount of data to the translucency of the available color materials. In this paper, we propose an error diffusion halftoning approach to achieve full color with multi-jet printers, which operates on multiple isosurfaces or layers within the object. We propose a novel traversal algorithm for voxel surfaces, which allows the transfer of existing error diffusion algorithms from 2D printing. The resulting prints faithfully reproduce colors, color gradients and fine-scale details.Comment: 15 pages, 14 figures; includes supplemental figure

Clustered-dot periodic halftone screen design and ICC profile color table compression

This dissertation studies image quality problems associated with rendering images in devices like printing or displaying. It mainly includes two parts: clustered-dot periodic halftone screen design, and color table compression. Screening is a widely used halftoning method. As a consequence of the lower resolution of digital presses and printers, the number of printer-addressable dots or holes in each microcell may be too few to provide the requisite number of tone lev- els between paper white and full colorant coverage. To address this limitation, the microcells can be grouped into supercells. The challenge is then to determine the desired supercell shape and the order in which dots are added to the microcell. Using DBS to determine this order results in a very homogeneous halftone pattern. To simplify the design and implementation of supercell halftone screens, it is common to repeat the supercell to yield a periodically repeating rectangular block called the basic screen block (BSB). While applying DBS to design a dot-cluster growth order- ing for the entire BSB is simpler to implement than is the application of DBS to the single non-rectangular supercell, it is computationally very inefficient. To achieve a more efficient way to apply DBS to determine the microcell sequence, we describe a procedure for design of high-quality regular screens using the non-rectangular super- cell. A novel concept the Elementary Periodicity Set is proposed to characterize how a supercell is developed. After a supercell is set, we use DBS to determine the micro-cell sequence within the supercell. We derive the DBS equations for this situation, and show that it is more efficient to implement. Then, we mainly focus on the regular and irregular screen design. With digital printing systems, the achievable screen angles and frequencies are limited by the finite addressability of the marking engine. In order for such screens to generate dot clusters in which each cluster is identical, the elements of the periodicity matrix must be integer-valued, when expressed in units of printer-addressable pixels. Good approximation of the screen sets result in better printing quality. So to achieve a better approximation to the screen sets used for commercial offset printing, irregular screens can be used. With an irregular screen, the elements of the periodicity matrix are rational numbers. In this section, first we propose a procedure to generate regular screens starting from midtone level. And then we describe a procedure for design of high-quality irregular screens based on the regular screen design method. We then propose an algorithm to determine how to add dots from midtone to shadow and how to remove dots from midtone to highlight. We present experimental results illustrating the quality of the halftones resulting from our design procedure by comparing images halftoned with irregular screens using our approach and a template-based approach. We also present the evaluation of the smoothness and improvement of the proposed methods. In the next part, we study another quality problem: ICC profile color table compression. ICC profiles are widely used to provide transformations between different color spaces in different devices. The color look-up tables (CLUTs) in the profiles will increase the file sizes when embedded in color documents. In this chapter, we discuss compression methods that decrease the storage cost of the CLUTs. For DCT compression method, a compressed color table includes quantized DCT coefficients for the color table, the additional nodes with large color difference, and the coefficients bit assignment table. For wavelet-based compression method, a compressed color table includes output of the wavelet encoding method, and the additional nodes with large color difference. These methods support lossy table compression to minimize the network traffic and delay, and also achieves relatively small maximum color difference

Media processor implementations of image rendering algorithms

Demands for fast execution of image processing are a driving force for today\u27s computing market. Many image processing applications require intense numeric calculations to be done on large sets of data with minimal overhead time. To meet this challenge, several approaches have been used. Custom-designed hardware devices are very fast implementations used in many systems today. However, these devices are very expensive and inflexible. General purpose computers with enhanced multimedia instructions offer much greater flexibility but process data at a much slower rate than the custom-hardware devices. Digital signal processors (DSP\u27s) and media processors, such as the MAP-CA created by Equator Technologies, Inc., may be an efficient alternative that provides a low-cost combination of speed and flexibility. Today, DSP\u27s and media processors are commonly used in image and video encoding and decoding, including JPEG and MPEG processing techniques. Little work has been done to determine how well these processors can perform other image process ing techniques, specifically image rendering for printing. This project explores various image rendering algorithms and the performance achieved by running them on a me dia processor to determine if this type of processor is a viable competitor in the image rendering domain. Performance measurements obtained when implementing rendering algorithms on the MAP-CA show that a 4.1 speedup can be achieved with neighborhood-type processes, while point-type processes achieve an average speedup of 21.7 as compared to general purpose processor implementations

Virtual electro-photographic printer model

A halftone image in the computer is a bitmap matrix that contains either 0 or 1 , where 0 means the printer will not deposit any toner onto a paper and 1 means the printer will deposit some amount of toner onto a paper. The amount of toner that is put by the printer onto a paper for a given input signal pattern is characterized. The hypothesis was that the distribution of toner mass on the paper for a given input matrix pattern can be modeled with a toner point spread function, a toner transfer efficiency function, and a noise function. In order to study toner mass distribution printed on paper, it is necessary to develop an analytical technique for measuring the distribution of toner mass. The analytical technique used in this thesis is an optical analysis based on light transmitted through the printed sample. This analytical technique was calibrated against a gravimetric analysis. Linear relation between the optical analysis and gravimetric analysis indicates that the technique can be used for measuring spatial distribution of printed toner mass on a micro-scale. Guided by experimental measurements of toner mass distribution, a quantitative model of the three printer functions, the spread function, the toner delivery function, and the noise function, were characterized. These functions were used to construct a printer function that was used to compare the efficiency of different halftone patterns. The result of the printer model was extended to include the optical point spread function of the paper. This provided a complete printing model that simulated both physical and optical dot gain

Digital Color Imaging

This paper surveys current technology and research in the area of digital color imaging. In order to establish the background and lay down terminology, fundamental concepts of color perception and measurement are first presented us-ing vector-space notation and terminology. Present-day color recording and reproduction systems are reviewed along with the common mathematical models used for representing these devices. Algorithms for processing color images for display and communication are surveyed, and a forecast of research trends is attempted. An extensive bibliography is provided