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Code Editor : Pixels.html

<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Magick++ API: Working with Pixels </title>
<link rel="stylesheet" href="magick.css" type="text/css" />
</head>
<body>
<div class="doc-section">
<h1 align="center">Magick::Pixels</h1>
The Pixels class provides efficient access to raw image
pixels. Image pixels (of type <a href="Quantum.html">Quantum</a>)
may be accessed directly via the Image Pixel Cache. The image
pixel cache is a rectangular window (a view) into the actual image
pixels (which may be in memory, memory-mapped from a disk file, or
entirely on disk). Obtain existing image pixels via get().
Create a new pixel region using set(). 
Depending on the capabilities of the operating system, and the
relationship of the window to the image, the pixel cache may be a copy
of the pixels in the selected window, or it may be the actual image
pixels. In any case calling sync() insures that the base image
is updated with the contents of the modified pixel cache. The method decode()supports
copying foreign pixel data formats into the pixel cache according to
the QuantumTypes. The method encode() supports copying
the pixels in the cache to a foreign pixel representation according to
the format specified by QuantumTypes. 
Setting a view using the Pixels class does not cause the number of
references to the underlying image to be reduced to one. Therefore, in
order to ensure that only the current generation of the image is
modified, the Image's <a href="Image++.html#modifyImage">modifyImage()</a>
method should be invoked to reduce the reference count on the underlying
image to one. If this is not done, then it is possible for a previous
generation of the image to be modified due to the use of reference
counting when copying or constructing an Image. 
The Quantum* returned by the set and get
methods, and the void* returned by the indexes
method point to pixel data managed by the Pixels class. The Pixels
class is responsible for releasing resources associated with the pixel
view. This means that the pointer should never be passed to delete() or
free(). 
The pixel view is a small image in which
the pixels may be accessed, addressed, and updated, as shown in the
following example, which produces an image similar to the one on the
right (minus lines and text): 
<img class="icon" src="Cache.png" name="Graphic1" align="bottom" width="254" border="0" />
<div class="viewport">
#include &lt;Magick++.h> 
#include &lt;iostream>

using namespace std; 
using namespace Magick; 
int main(int argc,char **argv) 
{ 
  InitializeMagick(*argv);

// Create base image 
  Image image(Geometry(254,218), "white");

// Set the image type to TrueColor DirectClass representation.
  image.type(TrueColorType);
  // Ensure that there is only one reference to underlying image 
  // If this is not done, then image pixels will not be modified.
  image.modifyImage();

// Allocate pixel view 
  Pixels view(image);

// Set all pixels in region anchored at 38x36, with size 160x230 to green. 
  size_t columns = 196; size_t rows = 162; 
  Color green("green"); 
  Quantum *pixels = view.get(38,36,columns,rows); 
  for ( ssize_t row = 0; row &lt; rows ; ++row ) 
    for ( ssize_t column = 0; column &lt; columns ; ++column ) 
    {
      *pixels++=QuantumRange*green.quantumRed();
      *pixels++=QuantumRange*green.quantumGreen();
      *pixels++=QuantumRange*green.quantumBlue();
    }

// Save changes to image.
  view.sync();

// Set all pixels in region anchored at 86x72, with size 108x67 to yellow. 
  columns = 108; rows = 67; 
  Color yellow("yellow"); 
  pixels = view.get(86,72,columns,rows); 
  for ( ssize_t row = 0; row &lt; rows ; ++row ) 
    for ( ssize_t column = 0; column &lt; columns ; ++column ) 
    {
      *pixels++=QuantumRange*yellow.quantumRed();
      *pixels++=QuantumRange*yellow.quantumGreen();
      *pixels++=QuantumRange*yellow.quantumBlue();
    }
   view.sync();

// Set pixel at position 108,94 to red 
  Color red("red");
  pixels = view.get(108,94,1,1);
  *pixels++=QuantumRange*red.quantumRed();
  *pixels++=QuantumRange*red.quantumGreen();
  *pixels++=QuantumRange*red.quantumBlue();

// Save changes to image.
 view.sync();
 image.write( "logo.png" );
}
</div>
Pixels supports the following
methods: 
Pixel Cache Methods
<table width="100%" border="1" cellpadding="2" cellspacing="2">
	<tbody>
 <tr>
		<td> 			
 Method
		</td>
		<td> 			
 Returns
		</td>
		<td> 			
 Signature
		</td>
		<td> 			
 Description
		</td>
	</tr>
	<tr>
		<td> 			
 <a name="get"></a>get
		</td>
		<td> 			
 <a href="Quantum.html">Quantum</a>*
		</td>
		<td> 			
 const ssize_t x_, const ssize_t y_, const size_t
columns_, const size_t rows_
		</td>
		<td> 			
 Transfers read-write pixels from the image to
the 			pixel cache as defined by the specified rectangular region.
			Modified pixels may be subsequently transferred back to the image
			via sync. The value returned is intended for pixel access
			only. It should never be deallocated.
		</td>
	</tr>
	<tr>
		<td> 			
 <a name="getConst"></a>getConst
		</td>
		<td> 			
 const <a href="Quantum.html">Quantum</a>*
		</td>
		<td> 			
 const ssize_t x_, const ssize_t y_, const size_t
			columns_, const size_t rows_
		</td>
		<td> 			
 Transfers read-only pixels from the image to
the 			pixel cache as defined by the specified rectangular region.
		</td>
	</tr>
	<tr>
		<td> 			
 <a name="set"></a>set
		</td>
		<td> 			
 <a href="Quantum.html">Quantum</a>*
		</td>
		<td> 			
 const ssize_t x_, const ssize_t y_, const size_t
			columns_, const size_t rows_
		</td>
		<td> 			
 Allocates a pixel cache region to store image
			pixels as defined by the region rectangle.  This area is
			subsequently transferred from the pixel cache to the image via 			sync.
The value returned is intended for pixel access only. 			It should
never be deallocated.
		</td>
	</tr>
	<tr>
		<td> 			
 <a name="sync"></a>sync
		</td>
		<td> 			
 void
		</td>
		<td> 			
 void
		</td>
		<td> 			
 Transfers the image cache pixels to the image.
		</td>
	</tr>
	<tr>
		<td> 			
 <a name="indexes"></a>indexes
		</td>
		<td> 			
 void*
		</td>
		<td> 			
 void
		</td>
		<td> 			
 Returns the PsuedoColor pixel indexes
			corresponding to the pixel region defined by the last <a href="Pixels.html#get">get</a>
			, <a href="Pixels.html#getConst">getConst</a>, or <a href="Pixels.html#set">set</a>
			call. Only valid for PseudoColor and CMYKA images. The pixel
			indexes (an array of type void, which is typedef 			Quantum,
which is itself typedef unsigned char, or 			unsigned short,
depending on the value of the QuantumDepth 			define) provide
the colormap index 			(see <a
 href="Image++.html#colorMap">colorMap</a>) for each pixel in 			the
image. For CMYKA images, the indexes represent the black 			
channel. The value returned is intended for pixel access 			only. It
should never be deallocated.
		</td>
	</tr>
	<tr>
		<td> 			
 <a name="x"></a>x
		</td>
		<td> 			
 int
		</td>
		<td> 			
 void
		</td>
		<td> 			
 Left ordinate of view
		</td>
	</tr>
	<tr>
		<td> 			
 <a name="y"></a>y
		</td>
		<td> 			
 int
		</td>
		<td> 			
 void
		</td>
		<td> 			
 Top ordinate of view
		</td>
	</tr>
	<tr>
		<td> 			
 <a name="columns"></a>columns
		</td>
		<td> 			
 size_t
		</td>
		<td> 			
 void
		</td>
		<td> 			
 Width of view
		</td>
	</tr>
	<tr>
		<td> 			
 <a name="rows"></a>rows
		</td>
		<td> 			
 size_t
		</td>
		<td> 			
 void
		</td>
		<td> 			
 Height of view
		</td>
	</tr>
 </tbody>
</table>
</div>
</body>
</html>

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Code Editor : Pixels.html