mlib_ImageSubsampleAveragemediaLib Library Fumlib_ImageSubsampleAverage(3MLIB)NAME
mlib_ImageSubsampleAverage, mlib_ImageSubsampleAverage_Fp - subsamples
an image with a box filter
SYNOPSIS
cc [ flag... ] file... -lmlib [ library... ]
#include <mlib.h>
mlib_status mlib_ImageSubsampleAverage(mlib_image *dst,
const mlib_image *src, mlib_d64 xscale, mlib_d64 yscale);
mlib_status mlib_ImageSubsampleAverage_Fp(mlib_image *dst,
const mlib_image *src, mlib_d64 xscale, mlib_d64 yscale);
DESCRIPTION
Each function scales an image down with an adaptive box filter.
The subsampling algorithm performs the scaling operation by averaging
all the pixel values from a block in the source image that correspond
to the destination pixel.
The width and height of the source block for a destination pixel are
computed as:
blockX = (int)ceil(1.0/xscale);
blockY = (int)ceil(1.0/yscale);
If we denote a pixel's location in an image by its column number and
row number (both counted from 0), the destination pixel at (i, j) is
backward mapped to the source block whose upper-left corner pixel is at
(xValues[i], yValues[j]), where
xValues[i] = (int)(i/xscale + 0.5);
yValues[j] = (int)(j/yscale + 0.5);
The width and height of the filled area in the destination are
restricted by
dstW = (int)(srcWidth * xscale);
dstH = (int)(srcHeight * yscale);
where srcWidth and srcHeight are width and height of the source image.
Since the block size in source is defined from scale factors with
roundup, some blocks (the rightmost and the bottommost blocks) may
overrun the border of the source image by 1 pixel. In this case, such
blocks are moved by 1 pixel to left/up direction in order to be inside
of the source image.
PARAMETERS
The function takes the following arguments:
dst Pointer to destination image.
src Pointer to source image.
xscale X scale factor. 0.0 < xscale ≤ 1.0.
yscale Y scale factor. 0.0 < yscale ≤ 1.0.
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_ImageSubsampleBinaryToGray(3MLIB), mlib_ImageFilteredSubsam‐
ple(3MLIB), mlib_ImageZoomTranslate(3MLIB), mlib_ImageZoomTrans‐
late_Fp(3MLIB), attributes(5)SunOS 5.10 2 Mar 2007 mlib_ImageSubsampleAverage(3MLIB)
