OK, thank you Wagner!<br>Well, my suggestion is in fact a correction. <br>In fact, it is a rather theoretical correction that I am sure it is not central to the purpose of this list,<br>so I think anyone who is not the guy who wrote the part of the ITK Guide of which I am about to talk
<br>can safely ignore the rest of the message.<br><br>Please take this as a humble attempt to contribute.<br><br>On to the subject: I am a teacher and researcher working in both image processing and information theory. While zapping through the guide I found a small section on Information Theory operators (page 663).
<br>The referred section is wrong in many ways, and I humbly think that being this package so popular among researchers, it is not good that it remains that way as it can bias the research direction of many people who happen to read it.
<br>This is what the section says:<br>--------------<br>Computing Image Entropy<br><br>The concept of Entropy has been introduced into image processing as a crude mapping from<br>its application in Communications. The notions of Information Theory can be deceiving and
<br>misleading when applied to images because their language from Communication Theory does<br>not necessarily maps to what people in the Imaging Community use.<br><br>For example, it is commonly said that<br>"The Entropy of an image is a measure of the amount of information contained in an image".
<br>This statement is fundamentally incorrect.<br><br>The way the notion of Entropy is commonly measured in images is by first assuming that the<br>spatial location of a pixel in an image is irrelevant! That is, we simply take the statistical
<br>distribution of the pixel values as it can be evaluated in a histogram and from that histogram we<br>estimate the frequency of the value associated to each bin. In other words, we simply assume<br>that the image is a set of pixels that are passing through a channel, just as things are commonly
<br>considered for communication purposes.<br>--------------<br><br>The first confusion is to say that a "zero order empirical entropy" is "the definition of entropy".<br>To be more specific: in Info Theory, Entropy is defined in terms of a *probabilistic model* for the data at hand. To consider pixels regardless of their position and relation to other pixels within the image is the simplest possible model and is widely known and accepted in both Info Theory and Image Processing fields that is highly innefective for almost any kind of image class. (*)
<br>"zero order" refers to the fact that the influence of "zero other pixels" is taken into account to *model* the probability of a given other pixel. *empirical* entropy refers to the fact that the entropy calculated is based on a probabilistic model fitted to empirical data, not a *real* probability, which is generally not available when modeling any kind of signal.
<br><br>It is also misleading to say that the ideas were "mapped" from "communications" to "image processing". The current theoretical framework of Info. Theory has long departed from its communication origins, and it is formulated as a general problem over any kind of data. The concept of "channel" is often used to model certain distortion processes that can modify images.
<br><br>It is also not true that the applications of information theory to image processing are in their early infancy. There is a lot of work to do, but algorithms such as the ones in the JPEG2000 or JPEG-LS image compression formats make heavy and effective use of advanced information theory concepts.
<br><br>There are also many effective applications of modern IT in segmentation (see <a href="http://citeseer.ist.psu.edu/leclerc94constructing.html">http://citeseer.ist.psu.edu/leclerc94constructing.html</a> for an example), texture simulation, restoration and denoising (which is what I have been doing as a researcher in the last two years) and many more areas.
<br><br><br>(*) Later in the next page there is a discussion of how the real concepts of IT should be used in image processing. The suggested directions, which are right, are being used since the 80's.<br><br><br>Thank you,
<br>Ignacio.<br><br><br><div><span class="gmail_quote">
2007/2/13, Wagner Sales <<a href="mailto:wsalles2003@yahoo.com.br" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">wsalles2003@yahoo.com.br</a>>:</span><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
-----BEGIN PGP SIGNED MESSAGE-----<br>Hash: SHA1<br><br>Ignacio,<br><br>First of all, take my answer just a suggestion ( I'm not a ITK<br>developer and not from Kitware ), but like experienced user, just try<br>to put the question here and may be someone can help you.
<br><br>Regards,<br><br>Wagner Sales<br><br><br>Ignacio Ramirez Paulino wrote:<br>> Hi, I am new to this list. Hi have a very specific suggestion<br>> regarding the ITK documentation. Should I post it here? I don't
<br>> want to subscribe to the developers list just for this.<br>><br>> -- --------------------------------------------------------------<br>> Ignacio Francisco Ramírez Paulino Magister en Ingeniería Eléctrica
<br>> --------------------------------------------------------------<br>> Instituto de Ingeniería Eléctrica Facultad de Ingeniería -<br>> Universidad de la República Tel: 598 2 7110974 x 117<br>> <a href="mailto:MSN:ignacio_francisco_ramirez_paulino@hotmail.com" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">
MSN:ignacio_francisco_ramirez_paulino@hotmail.com</a><br>> <mailto:<a href="mailto:MSN" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">MSN</a>:<a href="mailto:ignacio_francisco_ramirez_paulino@hotmail.com" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">
ignacio_francisco_ramirez_paulino@hotmail.com</a>> jabber:
<br>> <a href="mailto:ignacio_ramirez@jabber.org" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">ignacio_ramirez@jabber.org</a> <mailto:<a href="mailto:ignacio_ramirez@jabber.org" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">
ignacio_ramirez@jabber.org</a>><br>> Skype: ignacio_ramirez_paulino<br>> --------------------------------------------------------------
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http://www.itk.org/mailman/listinfo/insight-users</a><br></blockquote></div><br><br clear="all"><br>-- <br>--------------------------------------------------------------<br>Ignacio Francisco Ramírez Paulino<br>Magister en Ingeniería Eléctrica
<br>--------------------------------------------------------------<br>Instituto de Ingeniería Eléctrica<br>Facultad de Ingeniería - Universidad de la República<br>Tel: 598 2 7110974 x 117<br><a href="mailto:MSN:ignacio_francisco_ramirez_paulino@hotmail.com" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">
MSN:ignacio_francisco_ramirez_paulino@hotmail.com</a><br>jabber: <a href="mailto:ignacio_ramirez@jabber.org" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">ignacio_ramirez@jabber.org</a><br>Skype: ignacio_ramirez_paulino
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