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<h3 class="sectionHead"><span class="titlemark">1.4 </span> <a
id="x9-190001.4"></a>The <span
class="pcrr7t-">VMask </span>class</h3>
<!--l. 3--><p class="noindent" >The <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">VMask</span></span></span> class is an abstraction over the VIPS
<span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">DOUBLEMASK</span></span></span> and <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">INTMASK</span></span></span> types which gives convenient
and safe representation of matrices.
<!--l. 7--><p class="indent" > <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">VMask</span></span></span> has two sub-classes, <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">VIMask</span></span></span> and <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">VDMask</span></span></span>.
These represent matrices of integers and doubles
respectively.
<!--l. 10--><p class="noindent" >
<h4 class="subsectionHead"><span class="titlemark">1.4.1 </span> <a
id="x9-200001.4.1"></a>Constructors</h4>
<!--l. 12--><p class="noindent" >There are four constructors for <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">VIMask</span></span></span> and <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">VDMask</span></span></span>:
<div class="verbatim">
VIMask( int xsize, int ysize );
 <br />VIMask( int xsize, int ysize,
 <br />  int scale, int offset, ... );
 <br />VIMask( int xsize, int ysize,
 <br />  int scale, int offset,
 <br />  std::vector<int> coeff );
 <br />VIMask( const char ⋆name );
 <br />VIMask();
 <br />VDMask( int xsize, int ysize );
 <br />VDMask( int xsize, int ysize,
 <br />  double scale, double offset, ... );
 <br />VDMask( int xsize, int ysize,
 <br />  double scale, double offset,
 <br />  std::vector<double> coeff );
 <br />VDMask( const char ⋆name );
 <br />VDMask();
</div>
<!--l. 31--><p class="nopar" >
<!--l. 33--><p class="indent" > The first form creates an empty matrix, with the specified
dimensions; the second form initialises a matrix from
a varargs list; the third form sets the matrix from a
vector of coefficients; the fourth from the named file.
The final form makes a mask object with no contents
yet.
<!--l. 38--><p class="indent" > The varargs constructors are not wrapped in Python —
use the vector constructor instead. For example:
<div class="verbatim">
m = VMask.VIMask (3, 3, 1, 0,
 <br />  [-1, -1, -1,
 <br />   -1,  8, -1,
 <br />   -1, -1, -1])
</div>
<!--l. 46--><p class="nopar" >
<!--l. 48--><p class="noindent" >
<h4 class="subsectionHead"><span class="titlemark">1.4.2 </span> <a
id="x9-210001.4.2"></a>Projection functions</h4>
<!--l. 50--><p class="noindent" >A set of member functions of <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">VIMask</span></span></span> provide access to the
fields in the matrix:
<div class="verbatim">
int xsize() const;
 <br />int ysize() const;
 <br />int scale() const;
 <br />int offset() const;
 <br />const char ⋆filename() const;
</div>
<!--l. 59--><p class="nopar" >
<!--l. 61--><p class="indent" > <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">VDMask</span></span></span> is the same, except that the <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">scale()</span></span></span> and
<span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">offset()</span></span></span> members return <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">double</span></span></span>. <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">VMask</span></span></span> allows all
operations that are common to <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">VIMask</span></span></span> and <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">VDMask</span></span></span>.
<!--l. 65--><p class="noindent" >
<h4 class="subsectionHead"><span class="titlemark">1.4.3 </span> <a
id="x9-220001.4.3"></a>Assignment</h4>
<!--l. 67--><p class="noindent" ><span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">VMask</span></span></span> defines copy and assignment with pointer-style
semantics. You can write stuff like:
<div class="verbatim">
VIMask fred( "mask" );
 <br />VMask jim;
 <br />
 <br />jim = fred;
</div>
<!--l. 75--><p class="nopar" >
<!--l. 77--><p class="indent" > This reads the file <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">mask</span></span></span>, noting a pointer to the
mask in <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">fred</span></span></span>. It then makes <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">jim</span></span></span> also point to it, so
<span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">jim</span></span></span> and <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">fred</span></span></span> are sharing the same underlying matrix
values.
<!--l. 81--><p class="indent" > Internally, a <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">VMask</span></span></span> object is just a pointer to a
reference-counting block, which in turn holds a pointer to
the underlying VIPS <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">MASK</span></span></span> type. You can therefore
efficiently pass <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">VMask</span></span></span> objects to functions by value, and
return <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">VMask</span></span></span> objects as function results.
<!--l. 86--><p class="noindent" >
<h4 class="subsectionHead"><span class="titlemark">1.4.4 </span> <a
id="x9-230001.4.4"></a>Computing with <span
class="pcrr7t-">VMask</span></h4>
<!--l. 88--><p class="noindent" >You can use <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">[]</span></span></span> to get at matrix elements, numbered
left-to-right, top-to-bottom. Alternatively, use <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">()</span></span></span> to address
elements by <span
class="cmmi-10">x,y </span>position. For example:
<div class="verbatim">
VIMask fred( "mask" );
 <br />
 <br />for( int i = 0; i < fred.xsize(); i++ )
 <br />    fred[i] = 12;
</div>
<!--l. 97--><p class="nopar" >
<!--l. 99--><p class="noindent" >will set the first line of the matrix to 12, and:
<div class="verbatim">
VDMask fred( "mask" );
 <br />
 <br />for( int x = 0; x < fred.xsize(); x++ )
 <br />    fred(x, x) = 12.0;
</div>
<!--l. 107--><p class="nopar" >
<!--l. 109--><p class="noindent" >will set the leading diagonal to 12.
<!--l. 112--><p class="indent" > These don’t work well in Python, so there’s an extra
member, <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">get()</span></span></span>, which will get an element by <span
class="cmmi-10">x,y</span>
position.
<div class="verbatim">
x = mat.get (2, 4)
</div>
<!--l. 117--><p class="nopar" >
<!--l. 119--><p class="indent" > See the member functions below for other operations on
<span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">VMask</span></span></span>.
<!--l. 121--><p class="noindent" >
<h4 class="subsectionHead"><span class="titlemark">1.4.5 </span> <a
id="x9-240001.4.5"></a><span
class="pcrr7t-">VIMask </span>operations</h4>
<!--l. 123--><p class="noindent" >The following operations are defined for <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">VIMask</span></span></span>:
<div class="verbatim">
// Cast to VDMask and VImage
 <br />operator VDMask();
 <br />operator VImage();
 <br />
 <br />// Build gaussian and log masks
 <br />static VIMask gauss( double, double );
 <br />static VIMask gauss_sep( double, double );
 <br />static VIMask log( double, double );
 <br />
 <br />// Rotate
 <br />VIMask rotate45();
 <br />VIMask rotate90();
 <br />
 <br />// Transpose, invert, join and multiply
 <br />VDMask trn() ;
 <br />VDMask inv();
 <br />VDMask cat( VDMask );
 <br />VDMask mul( VDMask );
</div>
<!--l. 144--><p class="nopar" >
<!--l. 146--><p class="noindent" >
<h4 class="subsectionHead"><span class="titlemark">1.4.6 </span> <a
id="x9-250001.4.6"></a><span
class="pcrr7t-">VDMask </span>operations</h4>
<!--l. 148--><p class="noindent" >The following operations are defined for <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">VDMask</span></span></span>:
<div class="verbatim">
// Cast to VIMask and VImage
 <br />operator VIMask();
 <br />operator VImage();
 <br />
 <br />// Build gauss and log masks
 <br />static VDMask gauss( double, double );
 <br />static VDMask log( double, double );
 <br />
 <br />// Rotate
 <br />VDMask rotate45();
 <br />VDMask rotate90();
 <br />
 <br />// Scale to intmask
 <br />VIMask scalei();
 <br />
 <br />// Transpose, invert, join and multiply
 <br />VDMask trn();
 <br />VDMask inv();
 <br />VDMask cat( VDMask );
 <br />VDMask mul( VDMask );
</div>
<!--l. 171--><p class="nopar" >
<!--l. 173--><p class="noindent" >
<h4 class="subsectionHead"><span class="titlemark">1.4.7 </span> <a
id="x9-260001.4.7"></a>Output of masks</h4>
<!--l. 175--><p class="noindent" >You can output masks with the usual <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-"><<</span></span></span> operator.
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