version 0.04

# `quadtree.c`

``````  quadtree.c

Statistics in an arbitrary rectangle
l_int32   pixMeanInRectangle()
l_int32   pixVarianceInRectangle()

There are many other statistical quantities that can be computed
in a quadtree, such as rank values, and these can be added as
the need arises.

Similar results that can approximate a single level of the quadtree
can be generated by pixGetAverageTiled().  There we specify the
tile size over which the mean, mean square, and root variance
are generated; the results are saved in a (reduced size) pix.
Because the tile dimensions are integers, it is usually not possible
to obtain tilings that are a power of 2, as required for quadtrees.``````

# FUNCTIONS

BOXAA * boxaaQuadtreeRegions ( l_int32 w, l_int32 h, l_int32 nlevels )

``````  boxaaQuadtreeRegions()

Input:  w, h (of pix that is being quadtree-ized)
Return: baa (for quadtree regions at each level), or null on error

Notes:
(1) The returned boxaa has @nlevels of boxa, each containing
the set of rectangles at that level.  The rectangle at
level 0 is the entire region; at level 1 the region is
divided into 4 rectangles, and at level n there are n^4
rectangles.
(2) At each level, the rectangles in the boxa are in "raster"
order, with LR (fast scan) and TB (slow scan).``````

``````  fpixaDisplayQuadtree()

Input:  fpixa (mean, variance or root variance)
factor (replication factor at lowest level)
Return: pixd (8 bpp, mosaic of quadtree images), or null on error

Notes:
(1) The mean and root variance fall naturally in the 8 bpp range,
but the variance is typically outside the range.  This
function displays 8 bpp pix clipped to 255, so the image
pixels will mostly be 255 (white).``````

## pixMeanInRectangle

l_int32 pixMeanInRectangle ( PIX *pixs, BOX *box, PIX *pixma, l_float32 *pval )

``````  pixMeanInRectangle()

Input:  pix (8 bpp)
box (region to compute mean value)
pixma (mean accumulator)
&val (<return> mean value
Return: 0 if OK, 1 on error

Notes:
(1) This function is intended to be used for many rectangles
on the same image.  It can find the mean within a
rectangle in O(1), independent of the size of the rectangle.``````

l_int32 pixQuadtreeMean ( PIX *pixs, l_int32 nlevels, PIX *pix_ma, FPIXA **pfpixa )

``````  pixQuadtreeMean()

Input:  pixs (8 bpp, no colormap)
nlevels (in quadtree; max allowed depends on image size)
*pix_ma (input mean accumulator; can be null)
*pfpixa (<return> mean values in quadtree)
Return: 0 if OK, 1 on error

Notes:
(1) The returned fpixa has @nlevels of fpix, each containing
the mean values at its level.  Level 0 has a
single value; level 1 has 4 values; level 2 has 16; etc.``````

l_int32 pixQuadtreeVariance ( PIX *pixs, l_int32 nlevels, PIX *pix_ma, DPIX *dpix_msa, FPIXA **pfpixa_v, FPIXA **pfpixa_rv )

``````  pixQuadtreeVariance()

Input:  pixs (8 bpp, no colormap)
*pix_ma (input mean accumulator; can be null)
*dpix_msa (input mean square accumulator; can be null)
*pfpixa_v (<optional return> variance values in quadtree)
*pfpixa_rv (<optional return> root variance values in quadtree)
Return: 0 if OK, 1 on error

Notes:
(1) The returned fpixav and fpixarv have @nlevels of fpix,
each containing at the respective levels the variance
and root variance values.``````

## pixVarianceInRectangle

l_int32 pixVarianceInRectangle ( PIX *pixs, BOX *box, PIX *pix_ma, DPIX *dpix_msa, l_float32 *pvar, l_float32 *prvar )

``````  pixVarianceInRectangle()

Input:  pix (8 bpp)
box (region to compute variance and/or root variance)
pix_ma (mean accumulator)
dpix_msa (mean square accumulator)
&var (<optional return> variance)
&rvar (<optional return> root variance)
Return: 0 if OK, 1 on error

Notes:
(1) This function is intended to be used for many rectangles
on the same image.  It can find the variance and/or the
square root of the variance within a rectangle in O(1),
independent of the size of the rectangle.``````

l_int32 quadtreeGetChildren ( FPIXA *fpixa, l_int32 level, l_int32 x, l_int32 y, l_float32 *pval00, l_float32 *pval10, l_float32 *pval01, l_float32 *pval11 )

``````  quadtreeGetChildren()

Input:  fpixa (mean, variance or root variance)
level, x, y (of current pixel)
&val00, val01, val10, val11  (<return> child pixel values)
Return: 0 if OK, 1 on error

Notes:
(1) Check return value for error.  On error, all return vals are 0.0.
(2) The returned child pixels are located at:
level + 1
(2x, 2y), (2x+1, 2y), (2x, 2y+1), (2x+1, 2y+1)``````

l_int32 quadtreeGetParent ( FPIXA *fpixa, l_int32 level, l_int32 x, l_int32 y, l_float32 *pval )

``````  quadtreeGetParent()

Input:  fpixa (mean, variance or root variance)
level, x, y (of current pixel)
&val (<return> parent pixel value), or 0.0 on error.
Return: 0 if OK, 1 on error

Notes:
(1) Check return value for error.  On error, val is returned as 0.0.
(2) The parent is located at:
level - 1
(x/2, y/2)``````

l_int32 quadtreeMaxLevels ( l_int32 w, l_int32 h )

``````  quadtreeMaxLevels()

Input:  w, h (of image)
Return: maxlevels (maximum number of levels allowed), or -1 on error

Notes:
(1) The criterion for maxlevels is that the subdivision not
go down below the single pixel level.  The 1.5 factor
is intended to keep any rectangle from accidentally
having zero dimension due to integer truncation.``````

# AUTHOR

Zakariyya Mughal <zmughal@cpan.org>