[ITK-users] [ITK] itk vector Image pixel value

[Timothee Evain]

Hello Stefano

In this case, each pixel have multiples values, not only one, so to represent this, each pixel have for value a vector with multiples components.
Each component of the vector is an individual value.

Maybe an example is easier to understand. Think of a RGB image. You have three colors to represent, namely Red/Green/Blue.
You could represent it with 3 differents images, each with the value of Red, Green or Blue channel, or you could do it with only one image, where each pixel contain a vector. In this vector you will set the value of the Red/Green/Blue channel for the pixel. So you will have the "Red" component, the "Green" one, and the "Blue" at last.

A vector image is just the generalization of this.

HTH 

Tim

----- Mail original -----
De: "stefano serviddio" <s.serviddio at gmail.com>
À: insight-users at itk.org
Envoyé: Jeudi 24 Septembre 2015 13:36:27
Objet: [ITK] [ITK-users] itk vector Image pixel value

I have found this itk vector image example, I don't understand the meaning of each component of Vector Pixel type. 
For example the code line pixelValue[0] = 1.345; component X refers to a grayscale value or distance from next pixel inside the matrix of Image??? 


#include "itkVector.h"
// Software Guide : EndCodeSnippet
#include "itkImage.h"
int main(int, char *[])
{
  // Software Guide : BeginLatex
  //
  // The Vector class is templated over the type used to represent
  // the coordinate in space and over the dimension of the space.  In this example,
  // we want the vector dimension to match the image dimension, but this is by
  // no means a requirement. We could have defined a four-dimensional image
  // with three-dimensional vectors as pixels.
  //
  // \index{itk::Vector!Instantiation}
  // \index{itk::Vector!itk::Image}
  // \index{itk::Image!Vector pixel}
  //
  // Software Guide : EndLatex
  // Software Guide : BeginCodeSnippet
  typedef itk::Vector< float, 3 >       PixelType;
  typedef itk::Image< PixelType, 3 >    ImageType;
  // Software Guide : EndCodeSnippet
  // Then the image object can be created
  ImageType::Pointer image = ImageType::New();
  // The image region should be initialized
  const ImageType::IndexType start = {{0,0,0}}; //First index at {X,Y,Z}
  const ImageType::SizeType  size = {{200,200,200}}; //Size of {X,Y,Z}
  ImageType::RegionType region;
  region.SetSize( size );
  region.SetIndex( start );
  // Pixel data is allocated
  image->SetRegions( region );
  image->Allocate();
  // The image buffer is initialized to a particular value
  ImageType::PixelType  initialValue;
  // A vector can initialize all its components to the
  // same value by using the Fill() method.
  initialValue.Fill( 0.0 );
  // Now the image buffer can be initialized with this
  // vector value.
  image->FillBuffer( initialValue );
  const ImageType::IndexType pixelIndex = {{27,29,37}}; //Position {X,Y,Z}
  // Software Guide : BeginLatex
  //
  // The Vector class inherits the operator \code{[]} from the
  // \doxygen{FixedArray} class. This makes it possible to access the
  // Vector's components using index notation.
  //
  // Software Guide : EndLatex
  // Software Guide : BeginCodeSnippet
  ImageType::PixelType   pixelValue;
  pixelValue[0] =  1.345;   // x component
  pixelValue[1] =  6.841;   // y component
  pixelValue[2] =  3.295;   // x component
  // Software Guide : EndCodeSnippet
  // Software Guide : BeginLatex
  //
  // We can now store this vector in one of the image pixels by defining an
  // index and invoking the \code{SetPixel()} method.
  //
  // Software Guide : EndLatex
  // Software Guide : BeginCodeSnippet
  image->SetPixel(   pixelIndex,   pixelValue  );
  // Software Guide : EndCodeSnippet
  // The GetPixel method can also be used to read Vectors
  // pixels from the image
  ImageType::PixelType value = image->GetPixel( pixelIndex );
  std::cout << value << std::endl;
  // Lets repeat that both \code{SetPixel()} and \code{GetPixel()} are
  // inefficient and should only be used for debugging purposes or for
  // implementing interactions with a graphical user interface such as
  // querying pixel value by clicking with the mouse.
  return EXIT_SUCCESS;
} 

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