Degree of quantization and spatial addressability tradeoffs in perceived quality of color images

The objective of this thesis research was to investigate the tradeoffs between the number of quantization levels and spatial addressability of printed color images. Image quantization was done by employing the error-diffusion algorithm. The diffusion of error was performed in CMYK color space. The resulting images were printed on a color output device simulating different spatial addressabilities. To evaluate the perceived image quality, a psychophysical experiment was conducted followed by a statistical analysis of the experimental data. Based on the results of this analysis, the conclusions on the tradeoffs between the number of quantization levels and spatial addressability were drawn. It was determined that the tradeoffs were scene dependent with photographic scenes being able to sustain greater reduction in addressability without perceived image quality being decreased than graphics. The experiment showed that photographic scenes were sufficient to be printed with 5 bits per pixel per color at 100 dots per inch, and graphics with 3 bits per pixel per color at 300 dots per inch. If a single bits per color / dots per inch combination is to be named as the optimum combination equivalent to the best possible image for the given system (8bpc/300dpi), it would have to be 3bpc/300dpi. This combination was found to be equivalent to the quality of the best possible image at the normal viewing distance for all scenes in the experiment

Minimization of Halftone Noise in FLAT Regions for Improved Print Quality

The work in this thesis proposes a novel algorithm for enhancing the quality of flat regions in printed color image documents. The algorithm is designed to identify the flat regions based on certain criteria and filter these regions to minimize the noise prior and post Halftoning so as to make the hard copy look visibly pleasing. Noise prior to halftone process is removed using a spatial Gaussian filter together with a Hamming window, concluded from results after implementing various filtering techniques. A clustered dithering is applied in each channel of the image as Halftoning process. Furthermore, to minimize the post halftone noise, the halftone structure of the image is manipulated according to the neighboring sub-cells in their respective channels. This is done to reduce the brightness variation (a cause for noise) between the neighboring subcells. Experimental results show that the proposed algorithm efficiently minimizes noise in flat regions of mirumal gradient change in color images

Structure-aware halftoning

our result faithfully preserves the texture details as well as the local tone. All images have the same resolution of 445×377. This paper presents an optimization-based halftoning technique that preserves the structure and tone similarities between the original and the halftone images. By optimizing an objective function consisting of both the structure and the tone metrics, the generated halftone images preserve visually sensitive texture details as well as the local tone. It possesses the blue-noise property and does not introduce annoying patterns. Unlike the existing edge-enhancement halftoning, the proposed method does not suffer from the deficiencies of edge detector. Our method is tested on various types of images. In multiple experiments and the user study, our method consistently obtains the best scores among all tested methods.

Test Targets 6.0: A Collaborative effort exploring the use of scientific methods for color imaging and process control

Test Targets is a collection of scholarly papers contributed by faculty, students, and alumni of Rochester Institute of Technology. We realize the importance of having faculty set examples as authors for students to follow. We have a three-course sequence over a time span of a year to prepare students to publish their first articles when completing Tone and Color Analysis, Printing Process Control, and Advanced Color Management. In this instance, Test Targets 6.0 is a part of the course content in the Advanced Color Management course

Test Targets 3.1: A Collaborative effort exploring the use of scientific methods for color imaging and process control.

In general, test targets represent known values from an object or in a digital file, e.g., color patches, digital dots, lines with known dimensions, etc. The Macbeth ColorChecker is an analog target with 24 physical color patches. When captured by an input device and reproduced by an imaging system, we can compare tone and color relationships between the source target and its reproduction. On the other hand, the IT8.7/3 target is a digital file consisting of hundreds of patches with known CMYK digital values. When printed along side a signature, we can assess print quality quantitatively with the use of optical instruments and associated analysis techniques. - p. ii

FPGA BASED PARALLEL IMPLEMENTATION OF STACKED ERROR DIFFUSION ALGORITHM

Digital halftoning is a crucial technique used in digital printers to convert a continuoustone image into a pattern of black and white dots. Halftoning is used since printers have a limited availability of inks and cannot reproduce all the color intensities in a continuous image. Error Diffusion is an algorithm in halftoning that iteratively quantizes pixels in a neighborhood dependent fashion. This thesis focuses on the development and design of a parallel scalable hardware architecture for high performance implementation of a high quality Stacked Error Diffusion algorithm. The algorithm is described in ‘C’ and requires a significant processing time when implemented on a conventional CPU. Thus, a new hardware processor architecture is developed to implement the algorithm and is implemented to and tested on a Xilinx Virtex 5 FPGA chip. There is an extraordinary decrease in the run time of the algorithm when run on the newly proposed parallel architecture implemented to FPGA technology compared to execution on a single CPU. The new parallel architecture is described using the Verilog Hardware Description Language. Post-synthesis and post-implementation, performance based Hardware Description Language (HDL), simulation validation of the new parallel architecture is achieved via use of the ModelSim CAD simulation tool

A multiscale color error diffusion algorithm for color quantization

Centre for Multimedia Signal Processing, Department of Electronic and Information EngineeringRefereed conference paper2005-2006 > Academic research: refereed > Refereed conference paperVersion of RecordPublishe

Digital decoration of polymers : innovations in the dye sublimation process

There are numerous techniques that can be used for the decoration of polymeric substrates, dye sublimation, self-colouring, paint spraying, granular injection paint technology, pad printing, in-mould decoration and hot foil stamping. Dye sublimation was selected for this research as it was found to be both the most relevant technology area for IDT Systems Limited and the least understood. It is a customisable digital process which uses specialist Cyan, Magenta, Yellow and Black (CMYK) inkjet-able dyes that are transferred into a substrate via a carrier. During the process heat is applied which transforms the dyes from a solid into a gas phase. Analysis of literature identified a number of knowledge gaps, which are addressed during this research and detailed in this report. Initial experimentation concluded that the sublimation dyes can penetrate a range of commercially available amorphous polymers, comparably to semi-crystalline types. These findings dispute previously published work, but these also lacked rigorously recorded methodologies to confirm comparable data. All of the materials, equipment and methodologies used throughout this research were therefore developed in this report. Further detailed experimentation was completed, using amorphous polycarbonate, (PC) and semi-crystalline polybutylene terephthalate, (PBT) focusing on the process time and temperature to understand their influence on the level of dye penetration. The results revealed that increasing the process temperature and time improves the level of dye penetration and that comparable penetration levels were noted at 140-180 oC. Further research identified the importance of free volume in the polymer, this increases in size and connectivity as temperature increases above the glass transition points. Additional experimentation confirms that the free volume enables the dyes to penetrate into the polymer. Characterisation of the CMYK sublimation dyes was completed using Differential Scanning Calorimetry enabling the thermal transitions to be identified. Visual experimentation confirmed that the dyes start and finish sublimation between 145-210 oC. As no software tool existed to visualise the dye penetration, one was developed using MatLab. The tool imports and then interpolates the data and graphically outputs it for the user. This allows a quicker set up time of the process and reduces the number of samples to be destroyed. As a direct result of the innovations described in this report, the industrial sponsor has benefited with an increase in commercial exploitation. Aspects of this research have been published, presented and a patent has been published, details are provided within

Restoration of halftoned color-quantized images using linear estimator

Centre for Multimedia Signal Processing, Department of Electronic and Information EngineeringRefereed conference paper2006-2007 > Academic research: refereed > Refereed conference paperVersion of RecordPublishe