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From: ImageAnalyst <imageanalyst@mailinator.com>
Newsgroups: comp.soft-sys.matlab
Subject: Re: Help with image processing
Date: Tue, 3 Nov 2009 05:26:23 -0800 (PST)
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I'm not sure what code you used.  Did you try some sort of edge filter
like Sobel, Canny, or Difference of Gaussians?  You might have to
combine an edge detected image with other kinds of images, such as the
intensity image or a texture image (such as a variance filter or
something like that).  You can use imclose to do a morphological
closing to smooth and connect ragged boundaries.

You can get size if you know your field of view.  You will not be able
to get color unless you have a standard in your field of view, such as
the xrite Color Checker Chart.(http://www.xrite.com/
product_overview.aspx?ID=820).  This will enable you to compensate for
changes from picture to picture in illumination level and the "color
temperature" of your illumination (hopefully you know what that is).
Otherwise you're just using arbitrary units - you're just using the
"book formulas" which is no better than Photoshop.  It's totally
arbitrary and not accurate.  That is, if you got an CIE LAB color from
your MATLAB routine, it would not match the values that you would get
if you measured the actual fish via a spectrophotometer or
colorimeter.  Your "color reference card" doesn't appear to have any
colors in it so the best you can do is to compensate for overall
intensity level.  Even if it were color, there's only 3 patches and
this is not enough to do color correction (picture-to-picture rgb
correction) or color standardization (calibration, or rgb to CIE LAB
conversion).

You might also ask for algorithmic advice in sci.image.processing.
Regards,
ImageAnalyst