Brightness of Fine Detail in Ground Photography

Carman, P. D.; Brown, H. M.

doi:10.1364/josa.49.000629

Cited by 7 publications

(6 citation statements)

References 4 publications

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“…In their experiments, Carman and Carruthers (1951) set out to measure the various brightnesses throughout the brightness range of a particular target and also the brightness differences which occur in small detail at about the size which is just resolved by a metric camera with a 152 mm focal length lens. In order to do this, they employed opto-electrical devices and it is clear from their paper that difficulties in analysing the results were present (difficulties which do not occur in reading directly through the Hurter and Driffield curve when using real aerial photographs) and probably the extremely narrow angle telephotometer which they used recorded very low levels of brightness which do not break the threshold sensitivity of photographic emulsions and therefore do not appear in the negative.…”

Section: Discussion Of Resultsmentioning

confidence: 86%

“…The scene brightness range for a city, found in practical experiments by Carman and Carruthers (1951) and quoted by Eden (1964), is 1 : 9.5. This corresponds only at the lower end of the ranges found in these flight tests.…”

Section: Discussion Of Resultsmentioning

confidence: 99%

“…This difficulty is, to some extent, alleviated by the inverse feedback electronic printer and the density levels and contrasts suggested by Smith and Worton (1964) seem as valid now as when they were written. The brightness range of 1 : 9.5 found by Carman and Carruthers (1951) for the city of Halifax, Nova Scotia, seems to many workers in the field to be on the short side, while the range for shaded forested mountain of 1 : 99 seems to be on the long side. The measuring technique was different from that employed in these tests, as was the aircraft height and the solar altitude.…”

Section: Discussion Of Resultsmentioning

confidence: 99%

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Processing Aerial Films to Obtain Optimum Speed With Reduced Contrast

Worton

1980

The Photogrammetric Record

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Currently available black and white films are inherently too contrasty for medium scale and large scale urban area survey photography. Processing long lengths of 240 mm wide film in rewind spool tanks to establish suitable film/developer combinations and the subsequent analysis is a long, expensive and somewhat tedious procedure. A quick look method to establish suitable combinations is described using air exposed 70 mm wide film in a metric camera. Two films and three developers have been evaluated in this test. Most survey film negatives are accepted by their visual appearance and the opportunity has been taken to compare this subjective assessment with sensitometric measurement of film negative quality. The scene brightness range of survey target areas and the accommodation of long brightness ranges on available film is discussed briefly. Résumé Souvent les films noir et blancs sont de par nature trop contrastés pour prises de vue à moyenne ou grande échelle en milieu urbain. Plutôt que d'étudier la question pour les films 240 mm, ce qui seraitfort long et coûteux, on l'en fait pour des films 70 mm. On a étudié deux films et trots dévélateurs, la plupart des négatifs sont à l'oeil acceptables, et nous avons vérifié cette impression subjective par des measures sensitométriques. On discute le problème de la brillance du milieu et celui de la gamme de brillances sur les films acfuels. Zusammenfassung Die gegenwärtig verfügbaren Schwarz‐weiss‐Filme sind für Stadtaufnahmen in mittleren und grossen Massstäben zu hart. Die Verarbeitung sehr longer 240 mm breiter Filmbahnen in Umspulgeräten zur Ermittlung geeigneter Film‐Entwicklerkombinationen und die anschliessende Analyse ist ein langwieriges, teures und ermüdendes Verfahren. Beschreibung eines Schnellverfahrens zur Ermittlung passender Kombinationen, wobei ein in einer Messkammer belichteter Film benutzt wird. Insgesamt wurden zwei Filme und drei Entwickler untersucht. Die meisten Filmnegative wurden visuell bewertet, wobei diese subjektive Einschätzung mil der sensitometrischen Qu Messung der Qualität der Filmnegative verglichen wurde. Kurze Diskussion des Helligkeitsumfangs von Testgebieten und der en Wiedergabe auf den verfügbaren Filmen.

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Section: Discussion Of Resultsmentioning

confidence: 86%

Section: Discussion Of Resultsmentioning

confidence: 99%

Section: Discussion Of Resultsmentioning

confidence: 99%

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Processing Aerial Films to Obtain Optimum Speed With Reduced Contrast

Worton

1980

The Photogrammetric Record

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“…Unfortunately in the visual environment of the 'real world' object detail is typically at reduced contrast (see Carman & Brown 1959), with vision often being further adversely affected by a variety of factors ranging from intraocular light scatter to misty external (meteorological) conditions.…”

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confidence: 99%

The influence of level and polarity of figure‐ground contrast on vision

Pointer¹

2001

Acta Ophthalmologica Scandinavica

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ABSTRACT.Purpose: To document the effect upon human foveal vision of changes in the level and polarity of figure-ground contrast under photopic controlled test conditions, with particular emphasis on performance at low contrast levels. Methods: Using a forced-choice psychophysical paradigm, threshold acuity estimates were derived at 9 discrete levels over a near-3 octave contrast range for Landolt ring-type stimuli of either positive or negative polarity. Data were obtained under binocular conditions from 10 young adults, each wearing their optimum low myopic spectacle correction. Results: Visual acuity declined linearly with reducing stimulus contrast, the deterioration increasing substantially at ∞10% figure-ground contrast regardless of stimulus polarity. Performance was slightly (but not statistically significantly) better for positive contrast stimuli. Conclusion: Irrespective of contrast polarity, a reduction in stimulus figureground contrast ∞10% produces an accelerated decrement in photopic foveal vision compared to the performance at levels Ͼ10%. Some clinical and practical implications of this outcome are considered with regard to the examination of patients with normal and compromised visual function.

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“…Since, too, most detail in the normal visual environment is of low contrast (e.g. Carman and Brown, 1959), low-contrast letter acuity may well give a more useful indication of the visual problems suffered outside the consulting room by some patients. sensitivity is the reciprocal of the contrast threshold, so that the curves as plotted give the monocular contrast sensitivity function (CSF) of each eye.…”

mentioning

confidence: 99%

Visual assessment with low-contrast letter charts

1986

Ophthalmic and Physiological Optics

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Brightness of Fine Detail in Ground Photography

Cited by 7 publications

References 4 publications

Processing Aerial Films to Obtain Optimum Speed With Reduced Contrast

Processing Aerial Films to Obtain Optimum Speed With Reduced Contrast

The influence of level and polarity of figure‐ground contrast on vision

Visual assessment with low-contrast letter charts

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