Introducing a Model of Saliency Level, Based On Visual Complexity and Luminance Contrast with Implication in Urban Lighting

Dr. Steve Fotios Navaz Davoudian

Lecturer, Research in lighting and perception PhD candidate, Research in lighting and perception

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School of Architecture, University of Sheffield June 2007

New Tendencies in Urban Lighting in the Last Decades of 20^th Century Onward

• During last three decades, changes in people’s life styles enhanced the need to have more active nocturnal life. The modern style of life demands to extend the day life into the night atmosphere. As a result the city needs to be prepared to assure the same quality of life at day during the night besides solutions to fulfil the night life demands as well.
• Urban lighting is assumed as one of the most effective means to perform the above objectives. Lighting masterplans during last few decades, beside their functional view towards lighting, have been trying to generate pleasant night image and ambiance in cities. To achieve this goal one of their main objectives are to select the important urban objects and landmarks to be highlighted in the nocturnal image of the city.

School of Architecture, University of Sheffield June 2007

Light War and Visual Anarchy in Urban Areas

• In a study by Davoudian & Fotios (2006), they pointed the inadequacy of lighting masterplans in prevention of light war and visual anarchy in nightscape of the city by merely technical guidelines in urban lighting.

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• Traditionally, increasing luminance has been the main tool used to improve the saliency of a particular object. The studies and guidelines in this regards also are recommendations in about the luminance ratio between the object and its background to achieve different levels of conspicuity (saliency).

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• One of the reference guide books in this regard is ILE “Outdoor Lighting Guide” which has defined rules in terms of luminance ratio between object and background.

School of Architecture, University of Sheffield June 2007

Inadequacy of the Recommended Ratios Between Object and Background in Terms of Saliency

These recommendations are usually based on the conspicuity of the objects in front of the plane background. However, this is not exactly the same case when it comes to urban lighting in real situations.

School of Architecture, University of Sheffield June 2007

Background lighting patterns and visual complexity

• How Does Background Lighting Impact Saliency of Illuminated Objects?�
• How Does Background Complexity Impact Objects Saliency?

School of Architecture, University of Sheffield June 2007

Analysis of Visual Complexity

Structural Composition

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Analysis the Structural composition of the image

studies the scene without concerning about the meaning that the scene might carry for the observer and just considers the visual properties of the image.

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Having said this and look at the lighting of the scene as a composition of patterns, lead us to the question of how these patterns could influence our initial question of saliency. Several studies show that the background characteristics of the scene impacts the conspicuity of objects presented in the scene

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School of Architecture, University of Sheffield June 2007

Influential Factors in the Complexity of Background in Psychophysics Literature

Density Of Background Patterns

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• The number of the objects in the background reduces the observer ability to see the target.
• Increasing background density… has a significant effect for target detection by luminance contrast.

School of Architecture, University of Sheffield June 2007

Influential Factors in the Complexity of Background in Psychophysics Literature

Proximity of Background Patterns to the Target

• The interference from the distracters was only found when they were close to the target; beyond about 1°, they had little or no effect.
• But in the same time… distracters that share the target’s colour produce more interference than those that do not, and the effects of colour can be sufficiently strong to override those of proximity under some circumstances.

School of Architecture, University of Sheffield June 2007

Whether

• Salience of an Urban Object Varies with the Density of Background Lighting Patterns
• Salience of an Urban Object Varies with its Distance to Surrounding Lighting Patterns

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Research Questions

School of Architecture, University of Sheffield June 2007

Effect Of The Density Of Background Patterns of Light On The Conspicuity Of Urban Objects

• Independant Variables

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• Density of Background Patterns of Light

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• Luminance Contrast of Target to the Background

(CL = (LB-LT)/LB)

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School of Architecture, University of Sheffield June 2007

Effects Of Proximity of Background Patterns of Light to the Target

• Independant Variables

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• Proximity to the target object (degree visual angle)

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• Luminance Contrast of Target to the Background

(CL = (LB-LT)/LB)

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School of Architecture, University of Sheffield June 2007

Experimental Method 1: �Spatial Two-interval-forced Choice

Next Image

Next Image

Left or Right?

School of Architecture, University of Sheffield June 2007

Experimental Method 2: �Temporal Two-interval-forced Choice

Next Image

First or Second?

School of Architecture, University of Sheffield June 2007

Expected Outcomes

It is Expected to Introduce a Model of Saliency Level, Based On Level of Background Density of Light Patterns, Proximity of Background Patterns to the Urban Object and Luminance Contrast.

Saliency (%) = F(C_L) F(BGD)

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Saliency (%) = F(C_L) F(Prox.)

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School of Architecture, University of Sheffield June 2007

Who Would Benefit from This Study?

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• Lighting Masterplan Designers

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• Lighting Designers

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• Environmental Planners

School of Architecture, University of Sheffield June 2007

Navaz Davoudian

PhD candidate, School of Architecture, University of Sheffield

Western Bank,

Sheffield, UK

S10 2TN

E-Mail: N.Davoudian@shef.ac.uk

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Dr. Steve Fotios

Lecturer of Environmental Design & Sustainability

School of Architecture, University of Sheffield

Western Bank,

Sheffield, UK

S10 2TN

E-Mail: Steve.Fotios@shef.ac.uk

Lighting Research Group, University of Sheffield