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Solarisation (or solarization) is a phenomenon in photography in which the image recorded on a negative or on a photographic print is wholly or partially reversed in tone. Dark areas appear light or light areas appear dark. The term is synonymous with the Sabattier effect when referring to negatives, but is technically incorrect when used to refer to prints. In short, the mechanism is due to halogen ions released within the halide grain by exposure diffusing to the grain surface in amounts sufficient to destroy the latent image. ==The Sabattier effect== Initially, the term ''solarisation'' was used to describe the effect observed in cases of extreme overexposure of the negative in the camera. Most likely, the effect was first observed in scenery photographs including the sun (e.q. sol, sun). The sun, instead of being the whitest spot in the image, turned black or grey. See Minor White's: (The Black Sun 1955 ) The solarisation effect was already known to Daguerre and is one of the earliest known effects in photography. John William Draper was the first to call the overexposure effect solarisation. J.W.F. Herschel already observed the reversal of the image from negative to positive by extreme overexposure in 1840. ''L. Moser'' reported in 1843:"....., that the light in the camera obscura produces at first the well known negative image; with continued action of the light the image turns into a positive image.... and recently I have obtained in fact on occasion a third image which is negative". 〔Die Grundlagen der photographischen Prozesse mit Silberhalogeniden, Dr. Tomamichel ETH Zurich, Band 3, Akademischer Verlagsgesellschaft Frankfurt am Main 1968, page 1218〕 The effect generated in the dark room was then called ''pseudo-solarisation''. Spencer defines the Sabattier effect as: "Partial image reversal produced by brief exposure to white light of a partly developed silver halide image". Many other ways of chemical and actinic radiation "exposure" can be utilised for the partial image reversal. The use of chemicals for image reversal is also known as 'chemical fogging'. The ''pseudo-solarisation'' effect or ''Sabattier'' effect was described in print by ''H. de la Blanchere'' in 1859 in ''L’Art du Photographe''. It was described again in 1860 by ''L.M. Rutherford'' and ''C.A. Seely'',〔American Journal of Photography and the Allied Arts and Science. New Series, New York II (1860), page 251〕 separately, in successive issues of The ''American Journal of Photography'', and in the same year by ''Count Schouwaloff'' in the French publication ''Cosmos''. Sabatier published near the end of 1860 a process of obtaining direct positives, but according to the description, this process did not seem to have any connection with the Sabattier effect as no mentioning was made of any exposure of the Kollodium plates after development had started.〔Bulletin Societé Francaise de Photographie 6 (1860), page 312〕 The phenomenon should have been christened the Blanchere Effect, for it was not described by Sabatier correctly until 1862.〔Bulletin Societé Francaise de Photographie 8 (1862), page 175, 289〕〔Le Moniteur de la Photographie 2 (1862), pages 27, 45, 50〕 However, Sabatier could not find an explanation for the phenomena.〔Die Grundlagen der photographischen Prozesse mit Silberhalogeniden, Dr. Tomamichel ETH Zurich, Band 3, Akademischer Verlagsgesellschaft Frankfurt am Main 1968, page 1201〕 The effect was usually caused by accidentally exposing an exposed plate or film to light during developing. The artist Man Ray perfected the technique which was accidentally discovered in his darkroom by his assistant Lee Miller. It is evident from publications in the 19th century that this phenomenon was ''invented'' very many times by many photographers as it tends to occur whenever a light is switched on inadvertently in the darkroom while a film or print is being developed. In modern film photography, this effect can be emulated for artistic effect by briefly exposing the film to actinic light during chemical development. However, because of the speed of modern films, the effect is much more commonly seen in printing. There is a further characteristic effect: a narrow band or rim of low density, called the Mackie line, is formed at the boundaries between adjacent highlight and shadow areas. If the film negative is treated, the line is light, which produces a dark line in the print; when the print itself is processed it produces a white or light line around areas of high contrast. It is therefore always possible to determine whether the negative or print has been used to produce the solarisation effect.〔The Focal Encyclopedia of Photography, Revised Desk Edition 1969, page 1415〕 However, researchers have shown that ''Mackie lines'' are not part of the Sabattier effect itself. In scientific photography it was soon observed that when using photographic films with very high contrast (also known as lith films), the image produced by the Sabattier effect exhibited a multitude of lines of various width, representing a specific amount of exposure within a certain range. This led to the use of the Sabattier effect for obtaining first and second order equidensities for photogrametry and equidensitometry. Interpretation or measurement of an image is sometimes aided by simplification of the density pattern. By use of tone separation or equidensitometry a continuous-tone image can be converted into a single iso-density line delineating a contour of equal density.〔Applied Photography, Arnold et all, Focal Press, page 426〕 This results in data reduction and enables keying (areas or lines with iso-densities to unique patterns, grey values or colours). This keying to singular grey- or colour values is known in modern image processing as using L.U.T.s. Some applications for equidensitometry are: * Interferometry * Photoelastic Stress Analysis, using polarised light and birefringent models of the object under test.〔Applied Photography, Arnold et all, Focal Press, page 422〕 As said above, it is very difficult to manage all parameters for yielding consistent results when using the Sabattier effect and therefore other means of obtaining equidensities have been pursued.〔Applied Photography, Arnold et all, Focal Press, page 428〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Solarisation」の詳細全文を読む スポンサード リンク
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