Sunday, 19 July 2009

Alexandra Palace (crop) - Visibility Study

Viewing instructions: This video is best viewed in ‘full screen’ mode by clicking the ‘+’ icon in the bottom right of the image. You can use the time bar to speed up or slow down the video.

The visibility and appearance of buildings at a distance changes as a result of atmospheric effects. Factors include air moisture/relative humidity, particulate matter, wind direction, sun angle and elevation. The 10 second film above demonstrates the same scene viewed under different conditions.

The film starts with a photo taken in January: The contrast between foreground and background is less than in other conditions - due to low relative humidity, low particulate count, and winds from north. More definition and detail can be perceived on distant buildings in these conditions.

The film ends on a photo taken in July: Maximum contrast effect between foreground and background (i.e. perceived as least clear, objects at distance reading lighter) due to high relative humidity, high particulate count and winds from south east. High relative humidity results in extra moisture content in air and reduces the tonal range of buildings / landmarks viewed at distance.

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