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<title>IM_STDIF(3) manual page</title>
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<a href='#toc'>Table of Contents</a><p>
<h2><a name='sect0' href='#toc0'>Name</a></h2>
im_stdif, im_stdif_raw - statistical differentiation of an image
<h2><a name='sect1' href='#toc1'>Synopsis</a></h2>
<b>#include
<vips/vips.h></b>
<p> int im_stdif(in, out, a, m0, b, s0, xw, yw) <br>
IMAGE *in, *out; <br>
double a, m0, b, s0; <br>
int xw, yw;
<p> int im_stdif_raw(in, out, a, m0, b, s0, xw, yw) <br>
IMAGE *in, *out; <br>
double a, m0, b, s0; <br>
int xw, yw;
<p>
<h2><a name='sect2' href='#toc2'>Description</a></h2>
im_stdif() preforms statistical differencing according
to the formula given in page 45 of the book "An Introduction to Digital
Image Processing" by Wayne Niblack. This transformation emphasises the way
in which a pel differs statistically from its neighbours. It is useful for
enhancing low-contrast images with lots of detail, such as X-ray plates.
<p>
At point (i,j) the output is given by the eqn:
<p> vout(i,j) = a*m0 + (1-a)*meanv
+ <br>
(vin(i,j) - meanv) * (b*s0) / (s0+b*stdv)<br>
<p> Values a, m0, b and s0 are entered, while meanv and stdv are the values
calculated over a moving window of size xw, yw centred on pixel (i,j). m0
is the new mean, a is the weight given to it. s0 is the new standard deviation,
b is the weight given to it. Try:
<p> im_stdif $VIPSHOME/pics/huysum.v fred.v
0.5 128 0.5 50 11 11<br>
<p> The opreation works on one-band UCHAR images only, and writes a one-band
UCHAR image as its result. The output image has the same size as the input
- a black border is added to mark uncomputable pixels.
<p> im_stdif_raw() behaves
exactly as im_stdif(), but does not add the border of black pixels.
<p>
<h2><a name='sect3' href='#toc3'>Return
Value</a></h2>
All functions returns 0 on success and -1 on error.
<h2><a name='sect4' href='#toc4'>See Also</a></h2>
<a href='im_lhisteq.3.html'>im_lhisteq(3)</a>
,
<a href='im_histgr.3.html'>im_histgr(3)</a>
, <a href='im_hsp.3.html'>im_hsp(3)</a>
, <a href='im_heq.3.html'>im_heq(3)</a>
.
<h2><a name='sect5' href='#toc5'>Copyright</a></h2>
1991-1996, The National Gallery
and Birkbeck College <p>
<hr><p>
<a name='toc'><b>Table of Contents</b></a><p>
<ul>
<li><a name='toc0' href='#sect0'>Name</a></li>
<li><a name='toc1' href='#sect1'>Synopsis</a></li>
<li><a name='toc2' href='#sect2'>Description</a></li>
<li><a name='toc3' href='#sect3'>Return Value</a></li>
<li><a name='toc4' href='#sect4'>See Also</a></li>
<li><a name='toc5' href='#sect5'>Copyright</a></li>
</ul>
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