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Kaida Xiao, Chenyang Fu, Dimosthenis Karatzas and Sophie Wuerger. 2011. Visual Gamma Correction for LCD Displays. DIS, 32(1), 17–23.
Abstract: An improved method for visual gamma correction is developed for LCD displays to increase the accuracy of digital colour reproduction. Rather than utilising a photometric measurement device, we use observ- ers’ visual luminance judgements for gamma correction. Eight half tone patterns were designed to gen- erate relative luminances from 1/9 to 8/9 for each colour channel. A psychophysical experiment was conducted on an LCD display to find the digital signals corresponding to each relative luminance by visually matching the half-tone background to a uniform colour patch. Both inter- and intra-observer vari- ability for the eight luminance matches in each channel were assessed and the luminance matches proved to be consistent across observers (DE00 < 3.5) and repeatable (DE00 < 2.2). Based on the individual observer judgements, the display opto-electronic transfer function (OETF) was estimated by using either a 3rd order polynomial regression or linear interpolation for each colour channel. The performance of the proposed method is evaluated by predicting the CIE tristimulus values of a set of coloured patches (using the observer-based OETFs) and comparing them to the expected CIE tristimulus values (using the OETF obtained from spectro-radiometric luminance measurements). The resulting colour differences range from 2 to 4.6 DE00. We conclude that this observer-based method of visual gamma correction is useful to estimate the OETF for LCD displays. Its major advantage is that no particular functional relationship between digital inputs and luminance outputs has to be assumed.
Keywords: Display calibration; Psychophysics ; Perceptual; Visual gamma correction; Luminance matching; Observer-based calibration
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C. Alejandro Parraga, Jordi Roca, Dimosthenis Karatzas and Sophie Wuerger. 2014. Limitations of visual gamma corrections in LCD displays. Dis, 35(5), 227–239.
Abstract: A method for estimating the non-linear gamma transfer function of liquid–crystal displays (LCDs) without the need of a photometric measurement device was described by Xiao et al. (2011) [1]. It relies on observer’s judgments of visual luminance by presenting eight half-tone patterns with luminances from 1/9 to 8/9 of the maximum value of each colour channel. These half-tone patterns were distributed over the screen both over the vertical and horizontal viewing axes. We conducted a series of photometric and psychophysical measurements (consisting in the simultaneous presentation of half-tone patterns in each trial) to evaluate whether the angular dependency of the light generated by three different LCD technologies would bias the results of these gamma transfer function estimations. Our results show that there are significant differences between the gamma transfer functions measured and produced by observers at different viewing angles. We suggest appropriate modifications to the Xiao et al. paradigm to counterbalance these artefacts which also have the advantage of shortening the amount of time spent in collecting the psychophysical measurements.
Keywords: Display calibration; Psychophysics; Perceptual; Visual gamma correction; Luminance matching; Observer-based calibration
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Alicia Fornes, Beata Megyesi and Joan Mas. 2017. Transcription of Encoded Manuscripts with Image Processing Techniques. Digital Humanities Conference.441–443.
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Oriol Vicente, Alicia Fornes and Ramon Valdes. 2016. The Digital Humanities Network of the UABCie: a smart structure of research and social transference for the digital humanities. Digital Humanities Centres: Experiences and Perspectives.
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Josep Llados. 2007. Advances in Graphics Recognition. Digital Document Processing, Major Directions and Recent Advances, Advances in Pattern Recognition, B.B. Chaudhuri, ed., 281–304.
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Alicia Fornes, Josep Llados, Joan Mas, Joana Maria Pujadas-Mora and Anna Cabre. 2014. A Bimodal Crowdsourcing Platform for Demographic Historical Manuscripts. Digital Access to Textual Cultural Heritage Conference.103–108.
Abstract: In this paper we present a crowdsourcing web-based application for extracting information from demographic handwritten document images. The proposed application integrates two points of view: the semantic information for demographic research, and the ground-truthing for document analysis research. Concretely, the application has the contents view, where the information is recorded into forms, and the labeling view, with the word labels for evaluating document analysis techniques. The crowdsourcing architecture allows to accelerate the information extraction (many users can work simultaneously), validate the information, and easily provide feedback to the users. We finally show how the proposed application can be extended to other kind of demographic historical manuscripts.
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Jaime Lopez-Krahe, Josep Llados and Enric Marti. 2000. Architectural Floor Plan Analysis. University of Edinburgh.
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Marçal Rusiñol. 2006. A Model of Vectorial Signatures in Terms of Expressive Sub-Shapes: Symbol Indexation in Technical Documents.
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Jaume Rodriguez, S. Yacoub, Gemma Sanchez and Josep Llados. 2006. Performance Evaluation, Comparison and Combination of Commercial Handwriting Recognition Engines.
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Joan Mas. 2005. Syntactic approaches to recognize bi-dimensional shapes in graphics recognition. Application to sketching interfaces.
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