Changes between Version 10 and Version 11 of libpipi/research/filters


Ignore:
Timestamp:
08/22/2008 09:52:07 PM (16 years ago)
Author:
Sam Hocevar
Comment:

more stuff about the median

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  • libpipi/research/filters

    v10 v11  
    3131The third way to optimise a median filter is by accounting for the size of neighbourhood changes in raster scan order: usually only a few values are removed from and added to the list of neighbours. This becomes promising with large kernel sizes, and efficient algorithms exist that handle this case in 1D at least ![2].
    3232
    33 Methods for O(r) or O(log(r)) median filters have been commonly used so far. Even an O(1) method has recently been discovered [3]. However, they all seem to rely on histograms, which only works well when the input data consists of 8-bit integers. Since libpipi does most of its computations using 32-bit floats, such techniques are of limited usefulness.
     33Today, median filtering methods use O(r) techniques, but O(log(r)) ones exist, too [4].
     34
     35There is even a method in O(1) [3]. However, like many others, it relies on histograms, which only works well when the input data consists of 8-bit integers. Since libpipi does most of its computations using 32-bit floats, such techniques are of limited usefulness (but should be proposed anyway, because we have ways to tell whether an image has fewer than 8 bits per component).
     36
     37{{{
     38#!html
     39<p><span style="background: red; color: yellow; padding: 0 3px; font-weight: bold;">TODO</span> use ANYTHING but what we currently have... bubble sort, what the fuck!
     40}}}
    3441
    3542=== References ===
     
    3845 * ![2] Juhola, M.   Katajainen, J.   Raita, T., [http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=80784  Comparison of algorithms for standard median filtering], IEEE Transactions on Signal Processing, Volume 39, Issue 1, Jan 1991 pp. 204-208
    3946 * ![3] Perreault, S. Hebert, P., [http://nomis80.org/ctmf.html Median Filtering in Constant Time], in the September 2007 issue of IEEE Transactions on Image Processing
     47 * ![4]  Gil, J.   Werman, M., [http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=211471  Computing 2-D min, median, and max filters], IEEE Transactions on Pattern Analysis and Machine Intelligence, 15, 504-507, 1993
    4048
    4149=== Code ===