<title>Parallel error diffusion</title>

The effects of interstimulus and stimulus-specific factors on central (vs. peripheral) oblique effects were examined using classification, focusing, discrimination, and sequential same-different tasks. Classification results showed that grouping the vertical with the horizontal line and the two diagonal lines with each other facilitated performance. Discrimination results revealed that the two diagonal lines were more confusable with each other than were the members of any other stimulus pair. Focusing results indicated that the vertical and horizontal lines served as better focusing stimuli. A set of sequential same-different tasks, each using only two alternative stimuli, allowed for the examination of stimulus-specific factors in focusing; the effects of similarity relations between all stimuli in the total set were greatly reduced by the constrained context. The two diagonal lines were the most difficult to compare and proved to be the worst foci in these tasks as well. In conclusion, there are two factors operating in the central oblique effect: greater confusability between the two diagonal lines and more favorable stimulus-specific properties of vertical and horizontal lines.

Dot diffusion is an efficient approach which utilizes concepts of block-wise and parallel-oriented processing to generate halftones. However, the block-wise nature of processing reduces image quality much more significantly as compared to error diffusion. In this work, four types of filters with various sizes are employed in co-optimization procedures with class matrices of size 8 n 8 and 16 x 16 to improve the image quality. The optimal diffused weighting and area are determined through simulations. Many well-known halftoning methods, some of which includes direct binary search (DBS), error diffusion, ordered dithering, and prior dot diffusion methods, are also included for comparisons. Experimental results show that the proposed dot diffusion achieved quality close to some forms of error diffusion, and additionally, superior to the well-known Jarvis and Stucki error diffusion and Mese's dot diffusion. Moreover, the inherent parallel processing advantage of dot diffusion is preserved, allowing us to reap higher executing efficiency than both DBS and error diffusion.

This study explored the mechanisms that underlie asymmetries for the horizontal vertical illusion (HVI), which deceives length perception, so that a vertical line is perceived as longer than a horizontal line of equivalent length. In Experiment 1, university students (n=14) made length judgements for vertical and horizontal lines. The vertical line was shifted in eight steps from the far left of the horizontal line (⌊) to the far right (⌋). An HVI was observed for the medial positions (⊥), which diminished towards the lateral positions. The HVI was also stronger when the vertical line was on the left. Because the left/right asymmetry changed as a function of lateral/medial position, the asymmetry within the HVI stimulus is most likely the result of pseudoneglect, which affects judgements of horizontal length. In Experiment 2, participants (n=15) made judgements for HVI stimuli presented to the left- and right-hemispace and the midline. The HVI was stronger in the left hemispace. Because the asymmetry between the left- and right-hemispaces did not interact with the asymmetry within the stimuli, it was concluded that the asymmetry between hemispatial positions was the result of right hemisphere susceptibility to illusory geometrical effects whereas the asymmetry within the stimulus is related to an object-centred attentional asymmetry. The HVI is affected by asymmetries in length judgements and susceptibility to illusions and may provide interesting insights into attentional disorders in clinical populations, such as neglect.

Yorùbá language is one of the three main languages that is been spoken in Nigeria. It is a tonal language that carries an accent on the vowel alphabets. There are twenty-five (25) alphabets in Yorùbá language with one of the alphabets a digraph (GB). Due to the difficulty in typing handwritten Yorùbá documents, there is a need to develop a handwritten recognition system that can convert the handwritten texts to digital format. This study discusses the offline Yorùbá handwritten word recognition system (OYHWR) that recognizes Yorùbá uppercase alphabets. Handwritten characters and words were obtained from different writers using the paint application and M708 graphics tablets. The characters were used for training and the words were used for testing. Pre-processing was done on the images and the geometric features of the images were extracted using zoning and gradient-based feature extraction. Geometric features are the different line types that form a particular character such as the vertical, horizontal, and diagonal lines. The geometric features used are the number of horizontal lines, number of vertical lines, number of right diagonal lines, number of left diagonal lines, total length of all horizontal lines, total length of all vertical lines, total length of all right slanting lines, total length of all left-slanting lines and the area of the skeleton. The characters are divided into 9 zones and gradient feature extraction was used to extract the horizontal and vertical components and geometric features in each zone. The words were fed into the support vector machine classifier and the performance was evaluated based on recognition accuracy. Support vector machine is a two-class classifier, hence a multiclass SVM classifier least square support vector machine (LSSVM) was used for word recognition. The one vs one strategy and RBF kernel were used and the recognition accuracy obtained from the tested words ranges between 66.7%, 83.3%, 85.7%, 87.5%, and 100%. The low recognition rate for some of the words could be as a result of the similarity in the extracted features.

A digital micromirror device (DMD) provides 2D- and 3D-scene reconstruction by displaying diffractive and holographic optical elements. The highest frame rates (tens of thousands of Hz) can be achieved if the displayed optical elements are binarized. Except for DMD applications, hologram binarization is useful for display creation, image encryption, information compression and storage, fast 3D printing, etc. Error diffusion is one of the most qualitative implementations of hologram binarization. In this paper, three group's weighting matrices of error diffusion are analyzed: 16 standard, eight dot and six diagonal matrices. Thus, 30 error diffusion methods were used for optically recorded off-axis digital hologram binarization. The quality of the image reconstruction from the binarized holograms was compared. Direct applications of error diffusion with large weighting matrices and dot diffusion provide the highest reconstruction quality. Seven metrics were used as the error diffusion threshold. Twelve bypass directions of error diffusion were analyzed. In addition, the joint application of Otsu threshold and complex bypass directions allows us to improve the quality of hologram binarization by 15%.

This paper proposes an adaptive error diffusion algorithm for text enhancement followed by an efficient text segmentation that uses the maximum gradient difference (MGD). The gradients are calculated along with scan lines, then the MGD values are filled within a local window to merge text segments. If the value is above a threshold, the pixel is considered as potential text. Isolated segments are then eliminated in a non-text region filtering process. After the text segmentation, a conventional error diffusion method is applied to the background, while edge enhancement error diffusion is used for the text. Since it is inevitable that visually objectionable artifacts are generated when using two different halftoning algorithms, gradual dilation is proposed to minimize the boundary artifacts in the segmented text blocks before halftoning. Sharpening based on the gradually dilated text region (GDTR) then prevents the printing of successive dots around the text region boundaries. The method is extended to halftone color images to sharpen the text regions. The proposed adaptive error diffusion algorithm involves color halftoning that controls the amount of edge enhancement using a general error filter. However, edge enhancement unfortunately produces color distortion, as edge enhancement and color difference are trade-offs. The multiplicative edge enhancement parameters are selected based on the amount of edge sharpening and color difference. Plus, an additional error factor is introduced to reduce the dot elimination artifact generated by the edge enhancement error diffusion. In experiments, the text of a scanned image was sharper when using the proposed algorithm than with conventional error diffusion without changing the background.

The Neural Basis of Vertical and Horizontal Line Bisection Judgments: An fMRI Study of Normal Volunteers

The variation of individual synaptic transmission impacts the dynamics of complex neural circuits. We performed whole-cell recordings from monosynaptically connected hippocampal neurons in rat organotypic slice cultures using a synapse mapping method. The amplitude of unitary excitatory postsynaptic current (uEPSC) varied from trial to trial and was independent of the physical distance between cell pairs. To investigate the source of the transmission variability, we obtained patch-clamp recordings from intact axons. Axonal action potentials (APs) were reliably transmitted throughout the axonal arbour and showed modest changes in width. In contrast, calcium imaging from presynaptic boutons revealed that the amplitude of AP-evoked calcium transients exhibited large variations both among different boutons at a given trial and among trials in a given bouton. These results suggest that a factor contributing to the uEPSC fluctuations is the variability in calcium dynamics at presynaptic terminals. Finally, we acquired triple whole-cell recordings from divergent circuit motifs with one presynaptic neuron projecting to two postsynaptic neurons. Consistent with the independency of calcium dynamics among axonal boutons, a series of uEPSC fluctuations was not correlated between the two postsynaptic cells, indicating that different synapses even from the same neuron act independently.We conclude that the intra-bouton and inter-bouton variability in AP-induced calcium dynamics determine the heterogeneity and independency of uEPSCs.

Halftoning is a crucial part of image reproduction in print. For large format prints, especially at higher resolutions, it is important to have very fast and computationally feasible halftoning methods of good quality. The authors have already introduced an approach to obtain image-independent threshold matrices generating both first- and second-order frequency modulated (FM) halftones with different clustered dot sizes. Predetermined and image-independent threshold matrices make the proposed halftoning method a point-by-point process and thereby very fast. In this article, they report a comprehensive quality evaluation of first-and second-order FM halftones generated by this technique and compare them with each other, employing several quality metrics. These generated halftones are also compared with error diffusion (ED) halftones employing two different error filters. The results indicate that the second-order FM halftoning with small clustered dot size performs best in almost all studied quality aspects than the first-and second-order FM halftoning with larger clustered dot size. It is also shown that the first- and second-order FM halftones with small clustered dot sizes are of almost the same quality as ED halftones using Floyd–Steinberg error filter and of higher quality than halftones generated by ED employing Jarvis, Judice, and Ninke error filter.

A square composed of horizontal lines appears taller and narrower than an identical square made up of vertical lines. Reporting this illusion, Hermann von Helmholtz noted that such illusions, in which filled space seems to be larger than unfilled space, were common in everyday life, adding the observation that ladies' frocks with horizontal stripes make the figure look taller. As this assertion runs counter to modern popular belief, we have investigated whether vertical or horizontal stripes on clothing should make the wearer appear taller or fatter. We find that a rectangle of vertical stripes needs to be extended by 7.1% vertically to match the height of a square of horizontal stripes and that a rectangle of horizontal stripes must be made 4.5% wider than a square of vertical stripes to match its perceived width. This illusion holds when the horizontal or vertical lines are on the dress of a line drawing of a woman. We have examined the claim that these effects apply only for 2-dimensional figures in an experiment with 3-D cylinders and find no support for the notion that horizontal lines would be ‘fattening’ on clothes. Significantly, the illusion persists when the horizontal or vertical lines are on pictures of a real half-body mannequin viewed stereoscopically. All the evidence supports Helmholtz's original assertion.

We have previously developed a two-dimensional monochromatic halftoning with error diffusion neural networks (EDNs). We showed that EDNs find local minima of frequency-weighted error between a binary halftone output and corresponding smoothly varying input, an ideal framework for solving halftone problems. The advantage of the neural algorithm is that all pixel quantization decisions are computed in parallel and therefore the error diffusion process becomes un-directional and symmetric. Thus eliminates the artifacts caused by the traditional error diffusion method. This paper casts color halftoning as four related sub-problems: the first three are to compute good binary halftones for each primary color and the fourth is to simultaneously minimize frequency-weighted error in the luminosity of the composite result. We show that an EDN with a three-dimensional interconnect scheme can solve all four problems in parallel with user-adjustable emphasis on the relative importance of weighted error in luminosity. Our results show that the three-dimensional EDN matrix not only shapes the error to frequencies that human visual system (HVS) is least sensitive but also shapes the error in colors to which the HVS is least sensitive - namely it satisfies the minimum brightness variation criterion.

In this paper, we present a strategy and an FPGA implementation of a Connect6 player submitted to the FPT 2011 Design Competition. Connect6 is a two-player strategy board game. The winner of the game is the player who first gets six pieces of his color in a connected horizontal, vertical or diagonal line. We assign a strategic value to each potential move depending on the current board configuration. Our approach uses a minimal amount of situation dependent game logic in order to take full advantage of the available compute resources and parallelism. The FPGA implementation of this strategy always wins against the software opponent provided for the competition. Additionally, our implementation wins on average against different software AIs from [1], as long as no sophisticated game-tree search is performed by the software.

Background: To achieve accuracy and exact reproduction of prosthesis, choosing a perfect impression material is essential. Especially to make the prosthesis as accurately as possible, impression material should possess some essential properties, like; minimum dimensional changes, good flow ability and easy removal. Purpose: The aim of this study was to evaluate the accuracy and surface detail reproduction of Alginate and Addition Reaction Silicone as an impression materials. Method: This is an experimental in vitro study. In this study Impression by Alginate and Addition Reaction Silicone were made using a round stainless steel test block with three horizontal lines and two vertical lines. The horizontal lines were used for evaluating the surface detail reproduction, and vertical lines were provided for the dimensional accuracy. For dimensional accuracy the length of the middle horizontal line in between vertical lines and the distance between the top and bottom horizontal line was measured using travelling microscope. And for surface detail reproduction three horizontal line of one segment were observed under stereomicroscope. Result: According to study results Addition Reaction Silicone is better than Alginate regarding quality of impression. Conclusion: In comparison to Alginate, Addition Reaction Silicone might have better performance about accuracy and surface detail reproduction. DOI: http://dx.doi.org/10.3329/updcj.v3i2.17996 Update Dent. Coll. j: 2013; 3 (2): 28-33

Image data hiding is the hiding of invisible patterns in an image without degrading its visual quality. The hidden pattern can be visualized by overlaying the original image with watermarked ones or by applying an extraction algorithm. If the hidden pattern is visualized using the overlaying method, it can also be visualized using a simple XNOR operation. In the case that hidden data is extracted by a specific algorithm, it is commonly called steganography. In this paper we propose a method called dot diffusion with nonlinear thresholding (DDNT) to embed hidden data in halftone images, where the hidden data can be extracted by overlaying original and watermarked images or by performing the XNOR process on these two images. The main advantage of this method is that the hidden pattern's intensity can be adjusted by three parameters. The DDNT data hiding method utilizes the inherent parallelism in dot diffusion halftoning method, although it suffers from its lower visual quality than some other halftoning methods such as error diffusion

McCollough (1965) was the first to observe the visual effect that a pattern of vertical stripes on a red ground, alternating with a pattern of horizontal stripes on a green ground, has upon the subsequent perception of a test pattern of vertical and horizontal lines on a white ground. Observers usually report an apparent reddish color on the horizontal and a greenish color on the vertical portions of the neutral test pattern. This is know as the McCollough effect. Based on Hubel and Wiesel's observation (1959, 1968) that the visual system of the vertebrate contains edge detectors sensitive to line orientation, McCollough's model (1965) to explain the effect assumed that these detectors were color sensitive and subject to fatigue after successive stimulation, responding with decreased sensitivity to those wavelengths with which they had been most recently stimulated. According to McCollough, the effect was the result of a fatiguing of the verticalline detectors sensitive to red, a fatiguing such that the test pattern's vertical lines were then processed by the nonadapted vertical receptors for green and blue. Similarly, prolonged viewing of the horizontal pattern on green fatigued the horizontal-line detectors sensitive to green, so that the test pattern's horizontal lines appeared reddish. Stromeyer (1969) further observed that alternating a single pattern on a colored background with another, orthogonally oriented pattern on a neutral ground would also produce the usual McCollough effect. An inspection pattern of vertical lines on a red ground ('red verticals') alternated with an inspection pattern of horizontal lines on a white ground produced a greenish aftereffect on the verticals and a reddish aftereffect on the horizontals of a test pattern. Stromeyer explained his