25. Halftoning_screen - 2011

25. Halftoning_screen - 2011 - 4. Screening Advanced...

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Unformatted text preview: 4. Screening Advanced Digital Halftoning – 2 October 2011 4.1 Synopsis •  •  •  •  •  •  •  Screening architecture Screen taxonomy Screen descriptors Analysis of tone and detail Stochastic screens Periodic, clustered-dot screens (hybrid screen) Moire-free conditions for screen design Advanced Digital Halftoning – 2 October 2011 4.2 Screening is a Thresholding Process •  Simple point-to-point transformation of each pixel in the continuous-tone image to a binary value. •  Process requires no memory or neighborhood information. 1 1 1 1 111 331 331 11 Compare 1 ContinuousTone Image Halftone Image Threshold 0.5 3.5 2.5 1.5 Threshold Matrix Advanced Digital Halftoning – 2 October 2011 4.3 Why Not Use a Single Threshold? •  A single threshold yields only a silhouette representation of the image. •  No gray levels intermediate to white or black are rendered. •  To generate additional gray levels, the threshold must be dithered, i.e. perturbed about the constant value. Continuous-tone original image Advanced Digital Halftoning – 2 October 2011 Result of applying a fixed threshold at midtone 4.4 Basic Structure of Screening Algorithm 1 1 1 1 111 331 331 11 Compare 1 Halftone Image ContinuousTone Image 0.5 3.5 2.5 1.5 Threshold Matrix The threshold matrix is periodically tiled over the entire continuous-tone image. Advanced Digital Halftoning – 2 October 2011 4.5 Terminology •  The screening process is also called dithering. •  However, the term dithering is sometimes applied to any digital halftoning process, not just that consisting of a pixelto-pixel comparision with thresholds in a matrix. •  The following are equivalent terms for the threshold matrix: –  screen –  dither matrix –  mask Advanced Digital Halftoning – 2 October 2011 4.6 How Tone is Rendered •  If we threshold the screen against a constant gray value, we obtain the binary texture used to represent that constant level of absorptance. Advanced Digital Halftoning – 2 October 2011 4.7 Dot Profile Function •  The family of binary textures used to render each level of constant tone is called the dot profile function. •  There is a one-to-one relationship between the dot profile and the screen. Advanced Digital Halftoning – 2 October 2011 4.8 Selection of Threshold Values •  For an MxN halftone cell,can print 0, 1, 2, …, MN dots, yielding average absorptances 0, 1/MN, 2/MN, …, 1, respectively. •  As the input gray level increases, each time a threshold is exceeded, we add a new dot, thereby increasing the rendered absorptance by 1/MN. •  It follows that the threshold levels should be uniformly spaced over the range of gray values of the input image. Advanced Digital Halftoning – 2 October 2011 4.9 Rendering of Detail - Partial Dotting Advanced Digital Halftoning – 2 October 2011 4.10 Partial Dotting - Example Advanced Digital Halftoning – 2 October 2011 4.11 Spatial Arrangement of Thresholds •  For clustered dot textures, thresholds that are close in value are located close together in the threshold matrix Advanced Digital Halftoning – 2 October 2011 4.12 Spatial Arrangement of Thresholds (cont.) •  For dispersed dot textures, thresholds that are close in value are located far apart in the threshold matrix. Advanced Digital Halftoning – 2 October 2011 4.13 Detail Rendition with Dispersed Dot Screens •  Since the thresholds in any local neighborhood tend to be uniformly spread over the full range of gray levels, the gray level in that local neighborhood is rendered more accurately. Advanced Digital Halftoning – 2 October 2011 4.14 Clustered vs. Dispersed Dots Attribute Texture Visibility Detail Rendering Stability Clustered Dot High Fair High Dispersed Dot Low Good Low •  Note that these assessments are relative. •  For example, at sufficiently high resolution, clustered dot textures will also have low visibility and good detail rendition. Advanced Digital Halftoning – 2 October 2011 4.15 Macroscreen Design •  For a 128x128 screen, each threshold value between 0 and 255 occurs approximately 64 times in the matrix. •  Macroscreens are designed using search-based optimization strategies. •  The screen design is computationally intensive; but once the screen is obtained, images are still halftoned with one comparison/pixel. •  Macroscreens can be designed to have blue noise or green noise characteristics. •  These terms refer to the characteristics of the halftone textures generated by these screens, not the screens themselves. Advanced Digital Halftoning – 2 October 2011 4.16 Spectral Properties of Blue Noise Mask Highlight Texture Halftone texture Advanced Digital Halftoning – 2 October 2011 Fourier spectrum 4.17 Spectral Properties of Blue Noise Masks Midtone Texture Halftone texture Advanced Digital Halftoning – 2 October 2011 Fourier spectrum 4.18 Spectral Properties of Green Noise Masks Highlight Texture Halftone texture Advanced Digital Halftoning – 2 October 2011 Fourier spectrum 4.19 Spectral Properties of Green Noise Masks Midtone Texture Halftone texture Advanced Digital Halftoning – 2 October 2011 Fourier spectrum 4.20 Synopsis •  •  •  •  •  •  •  Screening architecture Screen taxonomy Screen descriptors Analysis of tone and detail Stochastic screens Periodic, clustered-dot screens (hybrid screen) Moire-free conditions for screen design Advanced Digital Halftoning – 2 October 2011 4.21 Iterative/Search-Based Methods for Screen Design •  Iterative/search-based methods for screen design may be categorized according to the domain and objective of the search: –  search domain »  dither(threshold) matrix »  dot profile function –  search objective »  minimize a cost function »  satisfy constraints •  The screen design methods that we will describe may be divided into four groups according to these descriptors. •  The intent of all these methods is to either directly or indirectly push the energy in the spectra of the binary textures away from the origin in the frequency domain, thus yielding a blue noise-like characteristic. •  [Spaulding, Miller, and Schildkraut, 1997] contains a good overview of some, but not all, of the screen designs discussed here. Advanced Digital Halftoning – 2 October 2011 4.22 Categorization of Methods for Screen Design Cost Function Constraints Search Objective Search Domain Dither Matrix Dot Profile Rolleston & Cohen, 1992 Mitsa & Parker, 1992 Dalton, 1989 Sullivan & Allebach & Ray, 1991 Stradling, 1979 Ulichney, 1993 Allebach & Lin, 1996 Advanced Digital Halftoning – 2 October 2011 4.23 Search Domains •  Dither matrix – we directly look for the best spatial arrangement of the thresholds. –  In this way, we simultaneously optimize the entire dot profile function. This suggests a greater liklihood of finding a global optimum. –  In practice, however, these algorithms do not perform as well as those based on level-by-level design of the dot profile function. •  Dot profile function – We design the levels in the dot profile function one at a time. –  Each new level must satisfy the stacking constraint with respect to the patterns that already have been designed. –  The design is greedy, since each successive level is more highly constrained. –  Several different sequences of levels have been tried. Advanced Digital Halftoning – 2 October 2011 4.24 Increasing absorptance Stacking Constraint Upper constraint level Level to be designed Lower constraint level Unconstrained pixels Advanced Digital Halftoning – 2 October 2011 4.25 Impact of order in which levels are designed for dot profile-based methods 0 255 128 64 32 192 96 160 224 When any given level is to be designed, the next lower and next higher levels that have already been designed serve as constraint levels for application of the stacking constraint. Advanced Digital Halftoning – 2 October 2011 4.26 Mitsa and Parker Screen •  [Mitsa and Parker, 1992] •  This algorithm employs a level-by-level iteration similar to that of Rolleston and Cohen algorithm to design a mask that satisfies constraints. •  The spatial domain constraint is that the texture at each level must be binary. The frequency domain constraint is that the radially averaged power spectrum have the prescribed blue noise shape as postulated by Ulichney, including the correct principal frequency. •  They determined empirically that scaling the principal frequency from that specified by Ulichney for a rectangular dot arrangement by a factor of K = 1 / 2 yielded improved textures. Advanced Digital Halftoning – 2 October 2011 4.27 Void and Cluster Screen •  [Ulichney, 1993] •  The algorithm employs a level-by-level search to minimize a cost function. •  It is based entirely in the spatial domain. •  Cost function is approximately C = max h[ m, n ] ∗ ∗ p( m, n; b ) − b m, n circ –  The filter h[m,n] can be interpreted as the point spread function of the human visual system; Ulichney used a Gaussian filter with s = 1.5 pixels. –  Convolution is circular to account for the periodicity of the dither matrix Advanced Digital Halftoning – 2 October 2011 4.28 Swapping pixels Location of tightest cluster Location of largest void c. swap hole closest to center of largest void with dot closest to center of tightest cluster. Before Move Advanced Digital Halftoning – 2 October 2011 After Move 4.29 Green Noise Screen Design Using spatial statistics (Lau et al.) Iterative manipulation of the halftone to attain desired pair-correlation statistics Modeled as Typical Pair Correlation curve for green noise halftones • If we construct a halftone with these characteristics, it will be green noise •  For the purpose of implementation, the pair correlation curve is modeled as a shaping function Advanced Digital Halftoning – 2 October 2011 Shaping function: Standard form K(r) •  Independent of λg •  λg ~ input parameter that controls coarseness of clusters •  During the design of halftone for any level, K(r) is scaled by λg to obtain the specific pair correlation that we want to attain 4.30 Impact of Dispersed Macroscreen Size •  As size of screen increases, visibility of fundamental period diminishes. •  Generally, a size between 128x128 and 256x256 is adequate. 16x16 pattern repeated 16x16 times Advanced Digital Halftoning – 2 October 2011 32x32 pattern repeated 8x8 times 4.31 Impact of Dispersed Macroscreen Size (cont.) 64x64 pattern repeated 4x4 times 128x128 pattern repeated 2x2 times Advanced Digital Halftoning – 2 October 2011 4.32 Importance of incorporating wrap-around in screen design Level: 15/255 No wraparound DBS Level: 90/255 Advanced Digital Halftoning – 2 October 2011 Level: 15/255 Level: 90/255 Wraparound DBS 4.33 Synopsis •  •  •  •  •  •  •  Screening architecture Screen taxonomy Screen descriptors Analysis of tone and detail Stochastic screens Periodic, clustered-dot screens (hybrid screen) Moire-free conditions for screen design Advanced Digital Halftoning – 2 October 2011 4.34 Hybrid Screen Topics [Lee and Allebach, 2007] •  Introduction To Hybrid Screen •  Bilevel Hybrid Screen Design •  Multilevel Hybrid Screen Design •  Experimental Results •  Color Hybrid Screen Design Advanced Digital Halftoning – 2 October 2011 4.35 Clustered-Dot Screen •  Gray levels are realized by changing the clustered-dot size (AM halftoning) •  Advantage –  Cluster is stable, robust to dot gain widely used for electrophotographic (EP) process •  Disadvantage –  Poor rendering details –  Limited gray levels contouring artifact Clustered-dot screen Dispersed-dot screen Advanced Digital Halftoning – 2 October 2011 4.36 Simple Clustered-Dot Screen a=127/255 a=16/255 a=0 Continuous-tone input Contouring Halftone using simple clustered-dot screen Advanced Digital Halftoning – 2 October 2011 4.37 Supercell Approach •  •  Supercell is a set of microcells together as a single screen Supercell is used To increase the number of gray levels To create more accurately angled screen microcell 02 with macrocell growing sequence 3 1 01 2 01 2 04 8 26 01 2 01 2 37 15 9 11 10 Increasing the gray levels Advanced Digital Halftoning – 2 October 2011 15.9° 14.93° Creating more accurately angled screen 4.38 Limitation on Supercell Periodic dot withdrawal pattern Abrupt texture change - Bayer structure Clustered-dot microcell with Bayer macrocell growing sequence Stochastic dot withdrawal pattern Homogeneous dot distribution Maze-like artifact Clustered-dot microscreen with stochastic-dispersed macrocell growing sequence Advanced Digital Halftoning – 2 October 2011 4.39 The Hybrid Screen •  The hybrid screen is a screening algorithm which generates stochastic dispersed-dot textures in highlights and shadows, and periodic clustereddot textures in midtones. Dispersed-dot Clustered-dot recursive ordering pattern regularly nucleated clusters blue noise green noise Periodic Stochastic Advanced Digital Halftoning – 2 October 2011 4.40 The Hybrid Screen (cont.) •  Two major idea for the hybrid screen: supercell + core •  To remove the maze-like artifact, a small region is defined as a “core” in each microcell. •  Inside the core, the original microcell growing sequence is ignored and the sequence can be randomized the first dot can move around within the core creates blue-noise-like texture No noticeable dot withdrawal pattern Blue-noise-like texture The hybrid screen – clustered-dot microcell with 2x2 core with DBS macrocell growing sequence Advanced Digital Halftoning – 2 October 2011 4.41 Parameter Specifications w w _ j _1 j _2 z z i i Orthogonal Screen Advanced Digital Halftoning – 2 October 2011 Nonorthogonal Screen 4.42 Microcell Design •  •  Microcell Design Procedure Continuous Parameter Halftone Cell Line Quantization Copy Boundaries Number of pixels in the microcell: Nmicro = |det N| = 17 w C C O C O O z B A B A (a) Advanced Digital Halftoning – 2 October 2011 B A (b) (c) 4.43 Supercell Design Basic screen block (BSB): Smallest rectangle tiled in vertical and horizontal directions Core size and shape: 4-pixel core when f ~ 140 to 190 lpi Microcell growing sequence 17 14 12 10 13 7 9 4 5 15 2 8 16 16 3 11 Cyan 15 5 94 17 14 Advanced Digital Halftoning – 2 October 2011 6 11 12 7 13 Magenta Highlight core pixels Midtone pixels Shadow core pixels ( a) 16 8 3 10 12 ( b) 4.44 Highlight and Shadow Design •  •  Highlight generation –  FM seeding: place one dot per core –  AM growing: grow each seed dot in the core Designing a level of the dot profile function •  Random toggle ( ~ Nmacro/Lmacro dots) Constrained DBS swap Index matrix for highlight •  Index matrix for shadows when the core shape is the same Advanced Digital Halftoning – 2 October 2011 After random toggle After swap (1 iteration) Final (5 iterations) 4.45 Hybrid Screen Generation •  Determining the macrocell growing sequence dmacro[m,n] –  Use the first dot-on sequence from FM seeding •  The index matrix for midtone: use composite screen index for supercell approach •  Index matrix generation 02 with macrocell growing sequence 3 1 microcell •  Screen generation 01 2 01 2 04 8 26 •  Halftoning operation 01 2 01 2 37 15 9 11 e.g. 9 = 4 X 2 + 1 Advanced Digital Halftoning – 2 October 2011 4.46 10 Multilevel Hybrid Screen Design •  Two approaches for creating multilevel hybrid screens Tile vectors are all integer-valued screen design by bilevel screen extension Tile vector contains non-integer value that corresponds to high resolution grid multilevel hybrid screen design using high resolution grid w Construct bilevel hybrid screen j z Extension to multilevel screen i 1. Multilevel hybrid screen by bilevel hybrid screen extension Advanced Digital Halftoning – 2 October 2011 2. Multilevel hybrid screen design using high resolution grid 4.47 Multilevel Hybrid Screen Design by Bilevel Hybrid Screen Extension •  Screen design by bilevel screen extension: tile vectors must be all integer-valued so that bilevel hybrid screen can be built Extension is done using the concept of anchor levels –  Anchor levels: Selected halftone patterns chosen from among the dot profile function of the bilevel hybrid screen Select 5 anchor levels: {pa0, pa1, pa2, pa3, pa4} = {p0, p1, p4, p6, p9} •  •  p0 p1 p2 p3 p4 p5 p6 p7 p8 p9 p0 p1 p4 p6 p9 •  Partial dot growing sequence p0 p1 Advanced Digital Halftoning – 2 October 2011 p4 p6 p9 4.48 Relation between bit depth and core size - 1 bpp Periodic texture Noticeable dot withdrawal pattern Supercell with Bayer macroscreen Hybrid screen with 1x1 core Blue-noise-like texture Dot withdrawal pattern removed Hybrid screen with 2x2 core Advanced Digital Halftoning – 2 October 2011 4.49 Relation between bit depth and core size - 2 bpp Texture is reduced, but still visible Comparable, but 2x2 is a little bit noisier than others Supercell with Bayer macroscreen Supercell with Bayer macroscreen Hybrid screen with 1x1 core Hybrid screen with 1x1 core Hybrid screen with 2x2 core Hybrid screen with 2x2 core 3 Levels 4 Levels Advanced Digital Halftoning – 2 October 2011 4.50 Relation between bit depth and core size - 4 bpp Supercell with Bayer macroscreen Clean texture No visible patterns Hybrid screen with 1x1 core Noisy texture Hybrid screen with 2x2 core Advanced Digital Halftoning – 2 October 2011 4.51 Rules of Thumb •  •  •  •  In bilevel hybrid screen, the hybrid screen with 2x2 core shows the best results in both smooth and detail mode. In multilevel hybrid screen, the extreme highlight pattern is greatly improved in Bayer and 1x1 core hybrid screen. On the other hand, the hybrid screen with 2x2 core appears noisier while growing from highlight to midtone due to stochastic texture As a conclusion, the core size should be decreased (stochastic pattern must be restricted) when 1.  Bit depth become higher 2.  The screen frequency become higher Advanced Digital Halftoning – 2 October 2011 4.52 Color Hybrid Screen Design •  To further improve the color texture, we jointly optimize color screens which has been separately designed. •  For the hybrid screen design, we can improve the highlight parts by developing the error metric for joint screens. •  Among four primary colorants (C, M, Y, K), we focus on two major colorants, C and M, because –  The joint optimization of these two colorants give as good a result as a design based on the joint optimization of CMY screens –  This two colorants are critical for skin tone Advanced Digital Halftoning – 2 October 2011 4.53 Color Hybrid Screen Framework C f [m , n ] Ra ndom T oggl e C l −1 p [m , n ] f M M [m , n ] Ra ndom T oggl e pl −1 [m , n ] e C MY [ m, n ] C _ p lM [m , n ] = g M [m , n ] p [m , n ] = g C [ m, n ] T T eMy [ m, n ] Y e [m , n ] D BS Sw a p T L um i na nc e Fi l t e r L um i na nc e Fi l t e r L um i na nc e Fi l t e r Chrom i na nc e Fi l t e r CM eC z [ m, n ] Chrom i na nc e Fi l t e r Advanced Digital Halftoning – 2 October 2011 1 Cha nne l 3 Cha nne l s Col or e rror i m a ge c re a t i on + CM eC x [m , n ] M e [m , n ] C eYy [m , n ] CM Yy e C MY [ m, n ] CM + _ C l M e C MY [ m, n ] D BS Sw a p e C [ m, n] C e Yy [m , n ] M e Yy [m , n ] CM Yy [ m, n ] e C M [m , n ] e Cx CM Yy [ m, n ] e || . || || . || || . || 2 EC 2 E 2 E YC M y 2 EC x 2 CM EC z + CM || . || || . || + M ∑ E= + α iE i i= C , , M MC + E CM = ∑ CM CM αj Ej j =Yy , x , z CC 4.54 Joint Screen Design Results Ramp halftoned with separately designed cyan screen Ramp halftoned with jointly designed cyan screen Advanced Digital Halftoning – 2 October 2011 4.55 Joint Screen Design Results Ramp halftoned with separately designed magenta screen Ramp halftoned with jointly designed magenta screen Advanced Digital Halftoning – 2 October 2011 4.56 Joint Screen Design Results CM ramp halftoned with separately designed screens CM ramp halftoned with jointly designed screens †Colors are modified to make cyan dots visible on the projector Advanced Digital Halftoning – 2 October 2011 4.57 Synopsis •  •  •  •  •  •  •  Screening architecture Screen taxonomy Screen descriptors Analysis of tone and detail Stochastic screens Periodic, clustered-dot screens (hybrid screen) Moire-free conditions for screen design Advanced Digital Halftoning – 2 October 2011 4.58 Most Common 4-Color CMYK Halftoning   Separately halftone each color with a different screen matrix   Overall Procedure: C Continuous-tone image M Continuous-tone image RGB Continuous-tone image Halftoning Halftoning ⊕ Y Continuous-tone image Halftoning K Continuous-tone image CMYK Halftone Halftoning superposed Example: http://en.wikipedia.org/wiki/Halftone separate halftones superposed color halftone Advanced Digital Halftoning – 2 October 2011 4.59 Halftone Representations in Spatial/Frequency Domains Using Periodic Clustered-Dot Screens   Continuous Space Fourier Transform (CSFT): the spectral representation of periodic clustereddot is “halftone spectral lattice” in the frequency domain. (as shown in the lower right figure) ~ tile vectors ~ periodicity matrix Periodic Clustered-Dot ~ fundamental frequencies ~ frequency matrix screen angle ~ intrascreen angle dot-per-inch, dpi Halftone spectral lattice Advanced Digital Halftoning – 2 October 2011 4.60 What is the Moiré Formation?   Amidror, 1994: •  (It is clear to describe moiré in the frequency domain) if the new frequency component that arrives from the superposition of two colorant planes locates in low-frequency region, there will be moiré. spatial domain + (d) frequency domain (c) (b) (a) = (e) + (f) = (unit: cycles/inch) : new frequency component Advanced Digital Halftoning – 2 October 2011 Isaac Amidror , Roger D. Hersch , Victor Ostromoukhov ,” Spectral analysis and minimization of moiré patterns in color separation ,” JEI, 1994. 4.61 When We Superpose Two Colorant Planes •  Moiré: the new low-frequency component that arrives from superposition One example of possible first-order moiré Advanced Digital Halftoning – 2 October 2011 4.62 How About High-Order Moiré in 2-Color Case? •  Moiré: the new low-frequency component that arrives from superposition One example of possible high-order moiré Advanced Digital Halftoning – 2 October 2011 4.63 First-Order Moiré-Free Conditions in 2-Color Case (check 8 new frequency components)   Moiré comes from low-frequency components.   First-order moiré-free condition in 2-color case: First-order moiré-free condition: 1 We need to check 8 composite frequencies. (blue arrows) 3 8 Periodic Clustered-Dot 2 5 4 7 6 : Fundamental frequencies Frequency Components : Sums and differences of fundamental frequencies Advanced Digital Halftoning – 2 October 2011 first-order case 4.64 Possible High-Order Moiré in 2-Color Case   First-order moiré-free condition checks: (Check 8 composite frequencies, shown as red lines)   Possible high-order moiré : (More than 8 composite frequencies) (First-order moiré: Frequency domain: ( an example of high-order moiré) Possible first-order moiré Possible high-order moiré : High-order frequency components : Fundamental frequencies : Sums and differences of fundamental frequencies : Linear combination of high-order fundamental frequencies Advanced Digital Halftoning – 2 October 2011 4.65 First-Order Moiré-Free Condition in 3-Color Case   In the 3-color case, we need to check: (moiré comes from superimposing 2 color separations) (a) First-order 2-color moiré-free condition: (any 2 different colors) (moiré comes from superimposing 3 color separations) (b) First-order 3-color moiré-free condition: (all 3 colors) Advanced Digital Halftoning – 2 October 2011 Example of 3-color case (shown in frequency domain) 4.66 Previous Approaches to Minimizing Visible Moiré in Color Printing   Traditional graphic arts industry (screen set of rotating identical, square screens):   Use set of 75°, 15°, 0°, and 45° for C,M,Y, and K   Amidror, 1994   Analyze moiré formation in the frequency domain   Propose idea of “first-order moiré”       Consider first-order moiré Baqai and Allebach, 2002 (3-color screen set)   Provide a framework to search for non-orthogonal moiré-free screens   Apply HVS to account for human viewer Search for non-orthogonal screens Shen-Ge Wang, 2003 (3-color screen set)   Derive conventional 3-color moiré-free conditions   Propose a 3-color moiré-free screen set First-order moiré-free condition Akira Ishii, 2003 (4-color screen set)   Propose idea of “sharing screen frequency”   4-color screen set which prevents moiré “sufficiently” (under 200 lpi)   Shen-Ge Wang, 2007 (3-color screen set)   Propose uniform hexagon moiré-free 3-color printing   Address high-order moiré-free case as “uniform hexagon”   Sharing screen frequency Shen-Ge Wang and Robert Loce, 2008 (N-color screen set)   Propose uniform hexagon moiré-free N-color printing Advanced Digital Halftoning – 2 October 2011 High-order moiré-free condition 4.67 Idea of Frequency Lattice-Based Screen [4]   We can solve N-color high-order moiré problems by using “frequency basis spectral lattice”: each time we select two lattice points (gray points) as one pair of fundamental frequency vectors of a colorant plane. Repeat this procedure until N-colorant (N pairs). One example of “frequency basis spectral lattice” (hexagonal frequency lattice): Frequency basis spectral lattice (frequency domain) :   Minimum frequency distance between any 2 lattice points: (predefined minimum permissible moiré frequency λ) Advanced Digital Halftoning – 2 October 2011 Shen-Ge Wang and R. P. Loce, “Uniform-rosette color halftoning for N-color moiré-free printing,” JEI, Apr. 2008. 4.68 Uniform Rosette Configuration C,M,K Screens Frequency Representation Moiré-free condition Uniform rosette configuration Advanced Digital Halftoning – 2 October 2011 4.69 Uniform Rosette Configuration – Digital Halftone CK CMK CM MK Advanced Digital Halftoning – 2 October 2011 4.70 70 ...
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25. Halftoning_screen - 2011 - 4. Screening Advanced...

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