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Image Iterators

General image iterator definition and implementations.

General image iterator definition and implementations.

The following tables describe the general requirements for image iterators and their iterator traits. The iterator implementations provided here may be used for any image data type that stores its data as a linear array of pixels. The array will be interpreted as a row-major matrix with a particular width.

Requirements for Image Iterators

Local Types Meaning
ImageIterator::value_typethe underlying image's pixel type
ImageIterator::PixelTypethe underlying image's pixel type
ImageIterator::reference the iterator's reference type (return type of *iter). Will be value_type & for a mutable iterator, and convertible to value_type const & for a const iterator.
ImageIterator::index_reference the iterator's index reference type (return type of iter[diff]). Will be value_type & for a mutable iterator, and convertible to value_type const & for a const iterator.
ImageIterator::pointer the iterator's pointer type (return type of iter.operator->()). Will be value_type * for a mutable iterator, and convertible to value_type const * for a const iterator.
ImageIterator::difference_type the iterator's difference type (vigra::Diff2D)
ImageIterator::iterator_category the iterator tag (vigra::image_traverser_tag)
ImageIterator::row_iteratorthe associated row iterator
ImageIterator::column_iteratorthe associated column iterator
ImageIterator::MoveXtype of the horizontal navigator
ImageIterator::MoveYtype of the vertical navigator
Operation Result Semantics
++i.x
i.x–
voidincrement x-coordinate
–i.x
i.x–
voiddecrement x-coordinate
i.x += dxImageIterator::MoveX & add dx to x-coordinate
i.x -= dxImageIterator::MoveX & subtract dx from x-coordinate
i.x - j.xint difference of the x-coordinates of i and j
i.x = j.xImageIterator::MoveX &i.x += j.x - i.x
i.x == i.ybool

j.x - i.x == 0

i.x < j.xbool

j.x - i.x > 0

++i.y
i.y++
voidincrement y-coordinate
–i.y
i.y–
voiddecrement y-coordinate
i.y += dyImageIterator::MoveY & add dy to y-coordinate
i.y -= dyImageIterator::MoveY & subtract dy from y-coordinate
i.y - j.yint difference of the y-coordinates of i and j
i.y = j.yImageIterator::MoveY &i.y += j.y - i.y
i.y == j.ybool

j.y - i.y == 0

i.y < j.yboolj.y - i.y > 0
ImageIterator k(i)copy constructor
k = iImageIterator &assignment
ImageIterator kdefault constructor
ImageIterator::row_iterator r(i)construction of row iterator
ImageIterator::column_iterator c(i)construction of column iterator
i += diffImageIterator & { i.x += diff.x
i.y += diff.y; }
i -= diffImageIterator & { i.x -= diff.x
i.y -= diff.y; }
i + diffImageIterator { ImageIterator tmp(i);
tmp += diff;
return tmp; }
i - diffImageIterator { ImageIterator tmp(i);
tmp -= diff;
return tmp; }
i - jImageIterator::difference_type { ImageIterator::difference_type tmp(i.x - j.x, i.y - j.y);
return tmp; }
i == jbool i.x == j.x && i.y == j.y
*iImageIterator::reference access the current pixel
i[diff]ImageIterator::index_reference access pixel at offset diff
i(dx, dy)ImageIterator::index_reference access pixel at offset (dx, dy)
i->member()depends on operation call member function of underlying pixel type via operator-> of iterator
i, j, k are of type ImageIterator
diff is of type ImageIterator::difference_type
dx, dy are of type int

Requirements for Image Iterator Traits

The following iterator traits must be defined for an image iterator:

Types Meaning
IteratorTraits<ImageIterator>::Iteratorthe iterator type the traits are referring to
IteratorTraits<ImageIterator>::iteratorthe iterator type the traits are referring to
IteratorTraits<ImageIterator>::value_typethe underlying image's pixel type
IteratorTraits<ImageIterator>::reference the iterator's reference type (return type of *iter)
IteratorTraits<ImageIterator>::index_reference the iterator's index reference type (return type of iter[diff])
IteratorTraits<ImageIterator>::pointer the iterator's pointer type (return type of iter.operator->())
IteratorTraits<ImageIterator>::difference_type the iterator's difference type
IteratorTraits<ImageIterator>::iterator_category the iterator tag (vigra::image_traverser_tag)
IteratorTraits<ImageIterator>::row_iteratorthe associated row iterator
IteratorTraits<ImageIterator>::column_iteratorthe associated column iterator
IteratorTraits<ImageIterator>::DefaultAccessor the default accessor to be used with the iterator
IteratorTraits<ImageIterator>::default_accessor the default accessor to be used with the iterator
IteratorTraits<ImageIterator>::hasConstantStrides whether the iterator uses constant strides on the underlying memory (always VigraTrueType for ImageIterators).

© Ullrich Köthe (ullrich.koethe@iwr.uni-heidelberg.de)
Heidelberg Collaboratory for Image Processing, University of Heidelberg, Germany

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