NAME
Image::Leptonica::Func::pixtiling
VERSION
version 0.04
pixtiling.c
pixtiling.c
PIXTILING *pixTilingCreate()
void *pixTilingDestroy()
l_int32 pixTilingGetCount()
l_int32 pixTilingGetSize()
PIX *pixTilingGetTile()
l_int32 pixTilingNoStripOnPaint()
l_int32 pixTilingPaintTile()
This provides a simple way to split an image into tiles
and to perform operations independently on each tile.
The tile created with pixTilingGetTile() can have pixels in
adjacent tiles for computation. The number of extra pixels
on each side of the tile is given by an 'overlap' parameter
to pixTilingCreate(). For tiles at the boundary of
the input image, quasi-overlap pixels are created by reflection
symmetry into the tile.
Here's a typical intended usage. Suppose you want to parallelize
the operation on an image, by operating on tiles. For each
tile, you want to generate an in-place image result at the same
resolution. Suppose you choose a one-dimensional vertical tiling,
where the desired tile width is 256 pixels and the overlap is
30 pixels on left and right sides:
PIX *pixd = pixCreateTemplateNoInit(pixs); // output
PIXTILING *pt = pixTilingCreate(pixs, 0, 1, 256, 30, 0);
pixTilingGetCount(pt, &nx, NULL);
for (j = 0; j < nx; j++) {
PIX *pixt = pixTilingGetTile(pt, 0, j);
SomeInPlaceOperation(pixt, 30, 0, ...);
pixTilingPaintTile(pixd, 0, j, pixt, pt);
pixDestroy(&pixt);
}
In this example, note the following:
- The unspecfified in-place operation could instead generate
a new pix. If this is done, the resulting pix must be the
same size as pixt, because pixTilingPaintTile() makes that
assumption, removing the overlap pixels before painting
into the destination.
- The 'overlap' parameters have been included in your function,
to indicate which pixels are not in the exterior overlap region.
You will need to change only pixels that are not in the overlap
region, because those are the pixels that will be painted
into the destination.
- For tiles on the outside of the image, mirrored pixels are
added to substitute for the overlap that is added to interior
tiles. This allows you to implement your function without
reference to which tile it is; no special coding is necessary
for pixels that are near the image boundary.
- The tiles are labeled by (i, j) = (row, column),
and in this example there is one row and nx columns.FUNCTIONS
pixTilingCreate
PIXTILING * pixTilingCreate ( PIX *pixs, l_int32 nx, l_int32 ny, l_int32 w, l_int32 h, l_int32 xoverlap, l_int32 yoverlap )
pixTilingCreate()
Input: pixs (pix to be tiled; any depth; colormap OK)
nx (number of tiles across image)
ny (number of tiles down image)
w (desired width of each tile)
h (desired height of each tile)
overlap (amount of overlap into neighboring tile on each side)
Return: pixtiling, or null on error
Notes:
(1) We put a clone of pixs in the PixTiling.
(2) The input to pixTilingCreate() for horizontal tiling can be
either the number of tiles across the image or the approximate
width of the tiles. If the latter, the actual width will be
determined by making all tiles but the last of equal width, and
making the last as close to the others as possible. The same
consideration is applied independently to the vertical tiling.
To specify tile width, set nx = 0; to specify the number of
tiles horizontally across the image, set w = 0.
(3) If pixs is to be tiled in one-dimensional strips, use ny = 1 for
vertical strips and nx = 1 for horizontal strips.
(4) The overlap must not be larger than the width or height of
the leftmost or topmost tile(s).pixTilingDestroy
void pixTilingDestroy ( PIXTILING **ppt )
pixTilingDestroy()
Input: &pt (<will be set to null before returning>)
Return: voidpixTilingGetCount
l_int32 pixTilingGetCount ( PIXTILING *pt, l_int32 *pnx, l_int32 *pny )
pixTilingGetCount()
Input: pt (pixtiling)
&nx (<optional return> nx; can be null)
&ny (<optional return> ny; can be null)
Return: 0 if OK, 1 on errorpixTilingGetSize
l_int32 pixTilingGetSize ( PIXTILING *pt, l_int32 *pw, l_int32 *ph )
pixTilingGetSize()
Input: pt (pixtiling)
&w (<optional return> tile width; can be null)
&h (<optional return> tile height; can be null)
Return: 0 if OK, 1 on errorpixTilingGetTile
PIX * pixTilingGetTile ( PIXTILING *pt, l_int32 i, l_int32 j )
pixTilingGetTile()
Input: pt (pixtiling)
i (tile row index)
j (tile column index)
Return: pixd (tile with appropriate boundary (overlap) pixels added),
or null on errorpixTilingNoStripOnPaint
l_int32 pixTilingNoStripOnPaint ( PIXTILING *pt )
pixTilingNoStripOnPaint()
Input: pt (pixtiling)
Return: 0 if OK, 1 on error
Notes:
(1) The default for paint is to strip out the overlap pixels
that are added by pixTilingGetTile(). However, some
operations will generate an image with these pixels
stripped off. This tells the paint operation not
to strip the added boundary pixels when painting.pixTilingPaintTile
l_int32 pixTilingPaintTile ( PIX *pixd, l_int32 i, l_int32 j, PIX *pixs, PIXTILING *pt )
pixTilingPaintTile()
Input: pixd (dest: paint tile onto this, without overlap)
i (tile row index)
j (tile column index)
pixs (source: tile to be painted from)
pt (pixtiling struct)
Return: 0 if OK, 1 on errorAUTHOR
Zakariyya Mughal <zmughal@cpan.org>
COPYRIGHT AND LICENSE
This software is copyright (c) 2014 by Zakariyya Mughal.
This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.