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more comments for the lbb resampler

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Nicolas Robidoux 2010-03-23 19:32:40 +00:00
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commit fefeec700f
1 changed files with 21 additions and 18 deletions
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libvips/resample/lbb.cpp
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@ -39,12 +39,17 @@
/*
* LBB (Locally Bounded Bicubic) is a high quality nonlinear variant
* of Catmull-Rom. Compared to Catmull-Rom, it produces resampled
* images with halos much reduced, both in terms of physical extent
* and over/undershoot amplitude. This is accomplished without
* noticeable changes to image smoothness.
* images with much reduced halos, both in terms of physical extent
* and over/undershoot amplitude. This is accomplished without a
* significant change in the smoothness of the result.
*
* Another important property is that the resampled values are
* contained within the range of nearby input values.
* contained within the range of nearby input values. Consequently, no
* clamping is needed to stay "in range."
*
* LBB was developed by Nicolas Robidoux and Chantal Racette of the
* Department of Mathematics and Computer Science of Laurentian
* University.
*/
/*
@ -59,6 +64,13 @@
*
* --It is interpolatory.
*
* --It is a Hermite bicubic method: The bicubic surface is defined,
* one convex hull of four nearby input points at a time, using
* four point values, four x-derivatives, four y-derivatives, and four
* cross-derivatives.
*
* --The stencil for values in a square patch is the usual 4x4.
*
* --It is C^1 with continuous cross derivatives.
*
* --It is locally bounded, in the following sense: Over each square
@ -70,27 +82,18 @@
* value and the very largest input pixel value. Consequently, it is
* not necessary to clamp results.
*
* --It is a Hermite bicubic method: The bicubic surface is defined,
* one convex hull of four nearby input points at a time, using the
* four point values, four x-derivatives, four y-derivatives, and four
* cross-derivatives.
*
* --The stencil for values in a square patch is the usual 4x4.
*
* --The LBB method is based on the method of Ken Brodlie, Petros
* Mashwama and Sohail Butt for constraining Hermite interpolants
* between globally defined planes:
*
* Visualization of surface data to preserve positivity and other
* simple constraints, Computer & Graphics, Vol. 19, #4, pages
* 585-594, 1995. DOI: 10.1016/0097-8493(95)00036-C.
* simple constraints. Computer & Graphics, Vol. 19, Number 4,
* pages 585-594, 1995. DOI: 10.1016/0097-8493(95)00036-C.
*
* The main novelty of the LBB method (besides its reliance on slope
* limiters for image resampling) lies in the fact that the method
* of Brodlie et al is used to enforce local, as opposed to global,
* boundedness. This method was developed by Nicolas Robidoux and
* Chantal Racette of the Department of Mathematics and Computer
* Science of Laurentian University.
* limiters in the context of image resampling) lies in the fact
* that the method of Brodlie et al is modified so as to enforce
* local, as opposed to global, boundedness.
*/
#ifdef HAVE_CONFIG_H