originally posted by: Imagewerx
a reply to: Indigent
It's not in the background which is quite hazy,the subject in this case is nice and clear so is quite close to the camera. (in between the trees and
Yes! While I wouldn't say that this is because the subject is "nice and clear", but rather because of it's "dark aspect".
This can be shown by measuring and comparing with each other the grey level of various objects of the scene.
Directly measurable data that quantify light received by a given pixel in the digital image are its gray level (along the black to white axis) and its
respective luminance levels in the 3 primary colors axes (red, green, blue). Those values characterize the apparent luminance of corresponding points
of the scene. In silver and digital photography, one may sometimes establish a correspondence formula – more or less empirical – between luminance
and gray level, through luminance calculations. Unfortunately this becomes practically impossible with JPEG format, because of all the optimization
real-time processing performed inside the camera before storing the image (RGB demastering, delinearization with application of gamma factor,
compression, accentuation, etc.).
For lack of means to estimate absolute luminance values, only relative calculations are possible, taking advantage reading across to monotonic level
variation according to apparent luminance.
Nevertheless, these empirical interpolations or extrapolations are invaluable in many cases, for they allow definition of a range of possible
distances of an object, by comparison with other elements of the scene that are located at known distances.
This is the case here, where we have mountains located at various distances. Then, we may consider that the darkest parts of the objects of the scene
were submitted to variations of their apparent luminance mostly due to atmospheric diffusion
. Consequently, we shall concentrate on the dark
part of the unidentified object (noted "1" below), as well as that of reference landscape areas (noted "2" to "5" below).
In a quite empirical approach, we shall content ourselves with noting down the darkest pixel value in each of these five areas, using a tool dedicated
to the analysis of the radiometry of pixels within in a closed surface.
We can clearly see that the atmospheric diffusion (sometimes called "haze") has a different impact on the dark aspect of the distant hill, depending
of their respective distance from the camera.
Assuming – which is highly probable – that the object and the reference landscape areas are really dark (this is not exactly true anyway for "2",
mainly green and not affected at all by atmospheric diffusion, like the unknown object, BTW), we may conclude that the distance of the object from the
camera was short and somewhere between that of a position somewhere above the foreground field and the first row of trees; possibly a little more far
Anyway, no way it can be a big object located at a distance equal to that of "3", "4" or "5".
(right click and open in a new tab for a better view)
edit on 11-7-2016 by elevenaugust because: (no reason given)