NICE : A Computational solution to close the gap from colour perception to colour categorization

The segmentation of visible electromagnetic radiation into chromatic categories by the human visual system has been extensively studied from a perceptual point of view, resulting in several colour appearance models. However, there is currently a void when it comes to relate these results to the physiological mechanisms that are known to shape the pre-cortical and cortical visual pathway. This work intends to begin to fill this void by proposing a new physiologically plausible model of colour categorization based on Neural Isoresponsive Colour Ellipsoids (NICE) in the cone-contrast space defined by the main directions of the visual signals entering the visual cortex. The model was adjusted to fit psychophysical measures that concentrate on the categorical boundaries and are consistent with the ellipsoidal isoresponse surfaces of visual cortical neurons. By revealing the shape of such categorical colour regions, our measures allow for a more precise and parsimonious description, connecting well-known early visual processing mechanisms to the less understood phenomenon of colour categorization. To test the feasibility of our method we applied it to exemplary images and a popular ground-truth chart obtaining labelling results that are better than those of current state-of-the-art algorithms

Reduction of visual acuity decreases capacity to evaluate radiographic image quality

Aim: To determine the impact of reduced visual acuity on the evaluation of a test object and appendicular radiographs. Methods: Visual acuity was reduced by two different magnitudes using simulation glasses and compared to normal vision (no glasses). During phase one phantom images were produced for the purpose of counting objects by 13 observers and on phase 2 image appraisal of anatomical structures was performed on anonymized radiographic images by 7 observers. The monitors were calibrated (SMPTE RP133 test pattern) and the room lighting was maintained at 7 ±1 lux. Image display and data on grading were managed using ViewDEX (v.2.0) and the area under the visual grading characteristic (AUCVGC) was calculated using VGC Analyzer (v1.0.2). Inferential statistics were calculated using SPSS. Results: For the evaluation of appendicular radiographs the total interpretation time was longer when visual acuity was reduced with 2 pairs of simulation glasses (15.4 versus 8.9 min). Visual grading analysis showed that observers can lose the ability to detect anatomical and contrast differences when they have a simulated visual acuity reduction, being more challenging to differentiate low contrast details. No simulation glasses, compared to 1 pair gives an AUCVGC of 0.302 (0.280, 0.333), that decreases to 0.197 (0.175, 0.223) when using 2 pairs of glasses. Conclusions: Reduced visual acuity has a significant negative impact on the evaluation of test objects and clinical images. Further work is required to test the impact of reduced visual acuity on visual search, technical evaluation of a wider range of images as well as pathology detection/characterization performance

E. Delacroix and J.M.W. Turner - The masters of the sublime, colour, and light during the first half of the 19th-century

Mellan Delacroix´s och Turners verk finns ibland en släktskap trots de stora skillnaderna i stil. Syftet med denna uppsats har varit att försöka fånga den känsla av likhet, som finns mellan några av deras verk, som uttrycker patos och kamp på liv och död mot naturens starka krafter eller människors ondska. Exempel på sådana verk är Delacroix´s Death of Sardanapalus, 1826 och Turners Slave Ship (Slavers Throwing Overboard the Dead and Dying, Thyphon Coming On), 1840 samt Delacroix´s The Lion Hunt, 1855 och Turners Whalers, 1845. Dessa verk ger uttryck för sublim storhet. Gemensamt för verken är också en högsta känsla för färgens måleriska möjligheter. Utvalda verk har analyserats med kontextuell metodik med avseende på sublimt innehåll utifrån estetiska teorier och litterära källor för det sublima enligt normerna för det akademiska måleriet i Frankrike och England under första hälften av 1800-talet. Uttryck för målerisk stil har studerats med formal metodik utifrån Ruskins och Wölfflins begrepp om det måleriska. I den formala analysen har även begrepp om komplementära färger ingått. Analysen visar att båda konstnärerna i flera avseenden inspirerats av såväl samma estetiska begrepp om det sublima, som av samma litterära klassiska och romantiska källor. Bådas stil blir alltmer expressiv med åren och deras senaste verk förebådar det moderna måleriet. Komplementära färger ingår i Delacroix´s senare stil. Släktskapet mellan Delacroix och Turner kan bäst sammanfattats utifrån Ruskins begrepp om det sublima.    Between Delacroix and Turner there is sometimes a kind of kinship as displayed in some of their works, although their great differences in style. The purpose of this thesis is an attempt to capture this feeling of similarity that can be found between some of their works expressing pathos including fights for life or death against the strong forces of Nature or the evil in Man. Examples of such works are Delacroix´s Death of Sardanapalus, 1826 and Turners Slave Ship (Slavers Throwing Overboard the Dead and Dying, Thyphon Coming On),1840 and Delacroix´s The Lion Hunt, 1855 and Turners Whalers, 1845. These work express sublime greatness. Common to the works are also the highest sense for the painterly possibilities of colour. Selected works have been analysed using a contextual method regarding contents of the sublime according to esthetical theories and literary sources of the sublime in agreement with the norms for the academic painting in France and England during the first half of the 19th century. Expressions of a painterly style have been studied using a formal method including the concepts of the painterly by John Ruskin and Heinrich Wölfflin. In the formal analysis also concepts of complementary colours have been studied. The analysis shows that both artists, in several ways, have been inspired by the same esthetical concepts of the sublime and the same literary classical and romantic sources. The painterly style of both artists becomes more expressive with age and their late works hint at the modern art to come. Complementary colours, are evident in the late style of Delacroix. The kinship between Delacroix and Turner can best be summarized by Ruskins words on the sublime