mlib_ImageFilteredSubsamplmediaLib Library Fmlib_ImageFilteredSubsample(3MLIB)NAME
mlib_ImageFilteredSubsample, mlib_ImageFilteredSubsample_Fp - antialias
filters and subsamples an image
SYNOPSIS
cc [ flag... ] file... -lmlib [ library... ]
#include <mlib.h>
mlib_status mlib_ImageFilteredSubsample(mlib_image *dst,
const mlib_image *src, mlib_s32 scaleX, mlib_s32 scaleY,
mlib_s32 transX, mlib_s32 transY,
const mlib_d64 *hKernel, const mlib_d64 *vKernel, mlib_s32 hSize,
mlib_s32 vSize, mlib_s32 hParity, mlib_s32 vParity, mlib_edge edge);
mlib_status mlib_ImageFilteredSubsample_Fp(mlib_image *dst,
const mlib_image *src, mlib_s32 scaleX, mlib_s32 scaleY,
mlib_s32 transX, mlib_s32 transY,
const mlib_d64 *hKernel, const mlib_d64 *vKernel, mlib_s32 hSize,
mlib_s32 vSize, mlib_s32 hParity, mlib_s32 vParity, mlib_edge edge);
DESCRIPTION
Each of the functions antialias filters and subsamples an image.
The effect of one of the functions on an image is equivalent to per‐
forming convolution (filter) followed by subsampling (zoom out).
The functions are similar to the mlib_ImageZoomTranslate() and
mlib_ImageZoomTranslate_Fp() functions. But they have different defini‐
tions on scale factors and translations, hence use different coordinate
mapping equations. The scaleX and scaleY used by mlib_ImageFilteredSub‐
sample() and mlib_ImageFilteredSubsample_Fp() are the reciprocals of
the zoomx and zoomy, respectively, used by mlib_ImageZoomTranslate()
and mlib_ImageZoomTranslate_Fp().
The functions use the following equations for coordinate mapping:
xS = xD*scaleX + transX
yS = yD*scaleY + transY
where, a point (xD, yD) in the destination image is backward mapped to
a point (xS, yS) in the source image. The arguments transX and transY
are provided to support tiling.
The subsample terms, i.e., the scale factors scaleX and scaleY, are
restricted to positive integral values. Geometrically, one destination
pixel maps to scaleX by scaleY source pixels. With odd scale factors,
destination pixel centers map directly onto source pixel centers. With
even scale factors, destination pixel centers map squarely between
source pixel centers. Below are examples of even, odd, and combination
cases.
s s s s s s s s s s s s
d d d
s s s s s s s d s s d s
s s s s s s s s s s s s
d d d
s s s s s s s s s s s s
s s s s s s s d s s d s
d d d
s s s s s s s s s s s s
Even scaleX/Y factors Odd scaleX/Y factors
s s s s s s s s s s s s
d d
s s s s s s s d s s d s s d s
s s s s s s s s s s s s
d d
s s s s s s s s s s s s
s s s s s s s d s s d s s d s
d d
s s s s s s s s s s s s
Odd/even scaleX/Y factors Even/odd scaleX/Y factors
where
s = source pixel centers
d = destination pixel centers mapped to source
The applied filter is quadrant symmetric (typically antialias + resam‐
ple). The filter is product-separable, quadrant symmetric, and is
defined by half of its span. Parity is used to signify whether the sym‐
metric kernel has a double center (even parity) or a single center
value (odd parity). For example, if hParity == 0 (even), the horizon‐
tal kernel is defined as:
hKernel[hSize-1], ..., hKernel[0], hKernel[0], ...,
hKernel[hSize-1]
Otherwise, if hParity == 1 (odd), the horizontal kernel is defined as:
hKernel[hSize-1], ..., hKernel[0], ...,
hKernel[hSize-1]
Horizontal and vertical kernels representing convolved resample (i.e.,
the combined separable kernels) can be computed from a convolution fil‐
ter (with odd parity), a resample filter, and because the subsample
factors affect resample weights, the subsample scale factors. It is the
user's responsibility to provide meaningful combined kernels.
To compute the value of a pixel centered at point (xD, yD) in the des‐
tination image, apply the combined kernel to the source image by align‐
ing the kernel's geometric center to the backward mapped point (xS, yS)
in the source image. In the cases that it can not be exactly on top of
point (xS, yS), the kernel's center should be half-pixel right and/or
below that point. When this is done in a separable manner, the centers
of horizontal and vertical kernels should align with xS and yS, respec‐
tively.
The combination of subsampling and filtering has performance benefits
over sequential fucntion usage in part due to the symmetry constraints
imposed by only allowing integer parameters for scaling and only allow‐
ing separable symmetric filters.
PARAMETERS
The function takes the following arguments:
dst Pointer to destination image.
src Pointer to source image.
scaleX The x scale factor of subsampling.
scaleY The y scale factor of subsampling.
transX The x translation.
transY The y translation.
hKernel Pointer to the compact form of horizontal kernel.
vKernel Pointer to the compact form of vertical kernel.
hSize Size of array hKernel.
vSize Size of array vKernel.
hParity Parity of horizontal kernel (0: even, 1: odd).
vParity Parity of vertical kernel (0: even, 1: odd).
edge Type of edge condition. It can be one of the following:
MLIB_EDGE_DST_NO_WRITE
RETURN VALUES
The function returns MLIB_SUCCESS if successful. Otherwise it returns
MLIB_FAILURE.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│Interface Stability │Committed │
├─────────────────────────────┼─────────────────────────────┤
│MT-Level │MT-Safe │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSOmlib_ImageSubsampleAverage(3MLIB), mlib_ImageZoomTranslate(3MLIB),
mlib_ImageZoomTranslate_Fp(3MLIB), attributes(5)SunOS 5.10 2 Mar 2007mlib_ImageFilteredSubsample(3MLIB)
