Halftone to continuous-tone conversion of error-diffusion coded images

Abstract Digital halftoning is a technique for converting a continuous-tone image into a quantized image to reproduce it on a digital printing device. Error diffusion (ED) is an algorithm that has proven to be effective for the halftoning process, and it has been widely applied to digital printing tasks. However, in images reproduced using conventional ED algorithms based on the signal processing theory, the texture of objects is often lost. In this study, we propose a texture-aware ED algorithm for multi-level digital halftoning. First, we generate multiple mapped images with different brightness levels through nonlinear transformation. For each mapped image, we adopt a texture-aware binary error diffusion method to obtain multiple halftone images. Finally, we generate a multi-level halftone image from the multiple halftone images. We test the algorithm on an actual printer, compare the results with those of the current raster image processor software and classical ED algorithms, and observe that our algorithm outputs better results.

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Effects of Dot Configuration on Color Reproduction and Anti-counterfeiting Features

Journal of Imaging Science and Technology ◽

10.2352/j.imagingsci.technol.2021.65.2.020502 ◽

2020 ◽

Author(s):

Raymond Chiang ◽

Pei-Li Sun

Keyword(s):

Screening Method ◽

Error Diffusion ◽

Color Management ◽

Shape Error ◽

Color Reproduction ◽

Two Stage ◽

Color Quality ◽

Raster Image ◽

Color Differences ◽

Continuous Tone

This study represents an attempt to solve the problem of color reproduction and identification for the prevention of stamp forgery. Generally, printed images are converted to halftone dot patterns by using a raster image processor. The amplitude-modulated dots of each separated color plane have a consistent shape such as conventional round, square, ellipse, or diamond shape; error diffusion occurs in frequency-modulated dots. To achieve anti-counterfeiting properties for stamp reproduction, two methods are proposed to obtain difficult-to-replicate dot structures and to provide corresponding color management methods. The first method involves arranging different dot shapes in different areas of an image. Color consistency is achieved using a virtual gray balance method. However, color differences are visible when two dot types are assigned to adjacent areas with similar colors. The second method is a two-stage screening method. The first screening stage defines different micro-regions in the image, which are then combined with the continuous-tone image again in the second screening step to assign different dot patterns to different micro-regions. This approach not only provides anti-counterfeiting ability but also ensures color consistency and allows controlling color quality using one ICC profile.

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Towards High-Resolution Copy-Evident Ceramic Tiles: A Deep Learning Framework for Halftoning and Watermarking

Electronics ◽

10.3390/electronics10151833 ◽

2021 ◽

Vol 10 (15) ◽

pp. 1833

Author(s):

Jianfeng Lu ◽

Zhiwen Wang ◽

Li Li ◽

Ching-Chun Chang ◽

Ting Luo ◽

...

Keyword(s):

High Resolution ◽

Interior Design ◽

Inkjet Printing ◽

Ad Hoc ◽

Error Diffusion ◽

Ceramic Tiles ◽

Invisible Watermarking ◽

Intractable Problems ◽

Continuous Tone ◽

Halftone Images

Ceramic art is essential in interior design and decoration, and making exquisite ceramic tiles imposes strict requirements for inkjet printing technology. High-resolution ceramic tiles are often produced through inkjet printing, in which the input images are converted into a halftone format. However, traditional binary halftoning techniques cannot produce high-resolution images for the ensuing printing process. Given that the processes of inkjet printing and high-temperature firing of ceramic tiles are a highly complex nonlinear system, and existing halftoning methods pose intractable problems, including inconsistent textures and color deviations. Based on a modified U-Net model and a modified error diffusion algorithm, we propose a multilevel halftoning method, which is capable of converting color-separation images of ceramic tiles into high-resolution halftone images. To deter copyright infringement, we further apply an ad hoc invisible watermarking method for halftone images. In this paper, we propose a four-stage framework: (1) A self-built dataset is used to solve non-convergence and overfitting problems caused by the unbalanced samples and non-uniqueness of halftone images. (2) A modified U-Net model is trained on the self-built dataset and applied to the ceramic-tile images. (3) An improved error diffusion algorithm is used to calibrate and convert the predicted continuous-tone transition images into multilevel halftone images for inkjet printing. (4) A invisible and robust watermark is embedding algorithm towards halftone images is proposed for copyright protection. Experimental results show that our methodology is effective for performing the color-to-halftone transformation and identifying the copyright.

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