mlib_ImageSubsampleBinaryTmediaLibLLibramlib_ImageSubsampleBinaryToGray(3MLIB)NAMEmlib_ImageSubsampleBinaryToGray - subsamples a binary image and con‐
verts it to a grayscale image
SYNOPSIS
cc [ flag... ] file... -lmlib [ library... ]
#include <mlib.h>
mlib_status mlib_ImageSubsampleBinaryToGray(mlib_image *dst,
const mlib_image *src, mlib_d64 xscale, mlib_d64 yscale,
const mlib_u8 *lutGray);
DESCRIPTION
The mlib_ImageSubsampleBinaryToGray() function subsamples a binary
(MLIB_BIT) image and converts it to a grayscale (MLIB_BYTE) image.
The subsampling algorithm performs the scaling operation by accumulat‐
ing all the bits in the source image that correspond to the destination
pixel and, based on the x and y scaling factors, reserving consecutive
indexes in the colormap for the maximum number of gray levels possible
in the destination image. The destination image pixel values of this
function are either gray levels or indexes (if lutGray==NULL).
For representing the source block of pixels that is used to determine
destination pixel values, the index 0 represents a block with no 1's
(all 0's), the index 1 represents a block with a single 1, and so on.
If the scaling factors require a fractional block of source pixels to
determine a destination pixel value, the block size is rounded up. For
example, if a 2.2-by-2.2 block of source pixels would be required to
determine destination pixel values, a 3-by-3 block is used, resulting
in 10 possible gray levels and therefore 10 colormap indexes, whose
values are 0 through 9.
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 . It must be of type MLIB_BYTE
and have just one channel.
src Pointer to source image. It must be of type MLIB_BIT and
have just one channel.
xscale X scale factor. 0.0 < xscale ≤ 1.0.
yscale Y scale factor. 0.0 < yscale ≤ 1.0.
lutGray Pointer to a grayscale lookup-table.
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_ImageZoomTranslateToGray(3MLIB), mlib_ImageSubsampleAver‐
age(3MLIB), attributes(5)SunOS 5.10 2 Mar mlib_ImageSubsampleBinaryToGray(3MLIB)
