[Insight-developers] Get/SetPixel() with taking an offset parameter

[Gaetan Lehmann]

Hi,

Currently, the GetPixel() and SetPixel() methods of the itk::Image class  
are taking a itk::Index parameter to know which pixel is concerned in the  
image.
The itk::Image also have the ComputeIndex() and ComputeOffset() methods to  
manipulate directly the offset in the buffer, and to convert this offset  
from/to an index.

Manipulating indexes in an algorithm (like in the current morphological  
reconstruction filters, in the component tree contribution I'm preparing  
(http://voxel.jouy.inra.fr/darcsweb/darcsweb.cgi?r=componentTree;a=summary),  
...) would be a lot more efficient, both in memory and in execution time,  
by using the offsets instead of the indexes: store an itk::Index cost 3  
long (with dim=3), while an offset is only 1, and there is no need to  
convert the offset to an index and the index to an offset.
Unfortunately, there is no Get/SetPixel() method able to work with an  
offset.

I think that it would be a good idea to implement them as follow (not  
tested yet, that's an example):



in itkImage.h:

void SetPixel(const OffsetValueType &offset, const TPixel& value)
   {
   (*m_Buffer)[offset] = value;
   }

const TPixel& GetPixel(const OffsetValueType &offset) const
   {
   return ( (*m_Buffer)[offset] );
   }

TPixel& GetPixel(const OffsetValueType &offset)
   {
   return ( (*m_Buffer)[offset] );
   }

TPixel & operator[](const OffsetValueType &offset)
   { return this->GetPixel(offset); }

const TPixel& operator[](const OffsetValueType &offset) const
   { return this->GetPixel(offset); }


void SetPixel(const IndexType &index, const TPixel& value)
   {
   typename Superclass::OffsetValueType offset = this->ComputeOffset(index);
   this->SetPixel( offset, value );
   }

const TPixel& GetPixel(const IndexType &index) const
   {
   typename Superclass::OffsetValueType offset = this->ComputeOffset(index);
   return this->GetPixel( offset );
   }

TPixel& GetPixel(const IndexType &index)
   {
   typename Superclass::OffsetValueType offset = this->ComputeOffset(index);
   return this->GetPixel( offset );
   }

TPixel & operator[](const IndexType &index)
   { return this->GetPixel(index); }

const TPixel& operator[](const IndexType &index) const
   { return this->GetPixel(index); }



in itkImageAdaptor.h:

void SetPixel(const IndexType &index, const PixelType & value)
   { m_PixelAccessor.Set( m_Image->GetPixel(index), value ); }

PixelType GetPixel(const IndexType &index) const
   { return m_PixelAccessor.Get( m_Image->GetPixel(index) ); }

PixelType operator[](const IndexType &index) const
   { return m_PixelAccessor.Get( m_Image->GetPixel(index) ); }


void SetPixel(const OffsetValueType &offset, const PixelType & value)
   { m_PixelAccessor.Set( m_Image->GetPixel(offset), value ); }

PixelType GetPixel(const OffsetValueType &offset) const
   { return m_PixelAccessor.Get( m_Image->GetPixel(offset) ); }

PixelType operator[](const OffsetValueType &offset) const
   { return m_PixelAccessor.Get( m_Image->GetPixel(offset) ); }



Does it seem reasonable to do that ?

Thanks,

Gaetan



-- 
Gaëtan Lehmann
Biologie du Développement et de la Reproduction
INRA de Jouy-en-Josas (France)
tel: +33 1 34 65 29 66    fax: 01 34 65 29 09
http://voxel.jouy.inra.fr