How far is something pictured from the camera?

Camera shake? No - this is an image with depth - three dimensions. It's a photograph of a train window - and what you're seeing is the reflection of the inside of the carriage. The 'trick' is that the window is double glazed - and you're seeing two images, one being the reflection in the inner pain and the other being the reflection in the outer plain - for a window is not a mirror, and the other evening it was reflecting about half of the light on the inside, and letting half pass straight through to the outer

As light travels in a straight line and reflects symmetrically, picture components further from the point of reflection will show with a greater offset.

But there aren't just two images .. there are further images, fainter, that you can see in the picture. This is where the light bounces back and forth between the two panes of glass before breaking through the inner pane to the camera lens.

I've seen this sort of thing before - way back in the early 1970s, I was involved with Seismic exploration for oil, where shock waves were generated on the surface, traveled down to the interfaces between different rock layers, where some was reflected back and some carried on through. By analyzing the returns, you can get a picture of rock interfaces deep below the surface. Once again, you see "multiples" with artificial extra returns. But actually the rock interfaces business - which looks for the shape of folds in the rock by taking a series of readings along a lines - is made very much more complex by the different speed that shock waves travel through different types of rock, and by the dampening effect of sand.

Filtering to remove multiples in seismic sections can be done through a deconvolution filter - and I don't see any reason why that couldn't be done pictures - perhaps someone has done so already. Sounds fun ... but not a project for me; I've too much plenty else to do.

(written 2011-02-15, updated 2011-02-19)

Associated topics are indexed under

G912 - Well House Consultants - Photography for the Web
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  [2224] Trowbridge - a missed opportunity? Melksham - into the breach? - (2009-06-08)
  [1895] Comparison - with and without flash - (2008-11-20)
  [1732] Old pictures and comparisons - (2008-08-01)
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  [1506] Ongoing Image Copyright Issues, PHP and MySQL solutions - (2008-01-14)
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  [1194] Drawing hands on a clock face - PHP - (2007-05-19)
  [1188] What shape is your shake? - (2007-05-15)
  [1185] Themes for the web site - (2007-05-13)
  [1114] PHP Image upload script - (2007-03-21)
  [1087] Telling a story in different ways - (2007-02-20)
  [937] Display an image from a MySQL database in a web page via PHP - (2006-11-22)
  [819] My projector has a photo-id - (2006-07-31)
  [665] PHP Image viewing application - (2006-04-01)
  [563] Merging pictures using PHP and GD - (2006-01-13)
  [553] Keep that image small - (2006-01-03)
  [546] The relevance of the hairy woodpecker - (2005-12-28)
  [194] Published Photographer - (2005-01-30)
  [97] What makes a professional photographer? - (2004-10-23)

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Train and boat journey - the passenger accommodation
How far is something pictured from the camera?
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