ausblenden:
Schlagwörter:
-
Zusammenfassung:
This thesis focuses on tone mapping operators and the perceptual differences
between them when the tone mapped images are compared with their corresponding
real-world views. To achieve this goal, two tone reproductions were implemented
within the scope of this thesis. High dynamic range (HDR) images were acquired
using the camera response curve recovery function of Robertson et al. for the
perceptual experiment. After the perceptual experiment, multivariate
statistical methods were used to analyze the set of data from the
psychophysical experiment.
Two tone reproductions, the Ashikhmin method and fast bilateral filtering
introduced by Durand and Dorsey were implemented. Both of them are classified
as local tone mapping techniques. Ashikhmin's method deals with the local
adaptation level and local contrast separately. The bilateral filtering method
is based upon the work of Tomasi and Manduchi and sped up by piece-wise linear
and subsampling strategies. This algorithm divides an image into two layers (a
base layer and a detail layer) in order to reduce contrast but preserve details.
In order to create HDR images, the camera response curve was recovered by using
the method of Robertson et al. Each HDR image was constructed from 15 images
with different exposures and saved in the Radiance RGBE format.
A psychophysical experiment was held with 14 human observers over seven tone
mapped images on two scenes.
The tone mapping operators are the followings: the linear tone mapping, the
fast bilateral filtering by Durand and Dorsey, Pattanaik et al.'s method, the
Ashikhmin method, the Ward method, the photographic tone reproduction of
Reinhard et al., and the adaptive logarithmic mapping of Drago et al.
In the psychophysical experiment, subjects were asked to compare each of the
images to its corresponding real-world view and rate its overall brightness,
contrast, detail reproduction in dark and bright regions, and naturalness. The
set of data was analyzed by using multivariate statistical analyses for the
main effect of the tone mapping operators.
The result shows that those tone mapping operators are perceived very
differently when compared with the corresponding real-world views.
The multivariate analysis of variance (MANOVA) shows that means of the set of
data are in a three-dimensional space but neither along a line nor on a plane.
An interesting result shown by this experiment is that those operators are
divided into global and local categories by Mahalanobis distances.
The main effects of the tone mapping operators to each of the attributes were
quite significant.
Overall brightness provides the biggest difference among the tone mapping
operators. The linear tone mapping operator was perceived with the highest
brightness and Pattanaik, Ward, and Drago also had a higher amount of overall
brightness than the others. Additionally, the result shows that although the
main effect of the tone mapping operators for the details in bright regions is
highly significant, for the details in dark regions is not.
Correlations of all of possible combination of the attributes were tested.
Regarding the naturalness, this research shows that none of the other
attributes has a strong influence by itself. This may suggest that naturalness
is influenced by a combination of the other attributes.
