Image::Leptonica::Func::conncomp
version 0.04
conncomp.c
conncomp.c Connected component counting and extraction, using Heckbert's stack-based filling algorithm. 4- and 8-connected components: counts, bounding boxes and images Top-level calls: BOXA *pixConnComp() BOXA *pixConnCompPixa() BOXA *pixConnCompBB() l_int32 pixCountConnComp() Identify the next c.c. to be erased: l_int32 nextOnPixelInRaster() l_int32 nextOnPixelInRasterLow() Erase the c.c., saving the b.b.: BOX *pixSeedfillBB() BOX *pixSeedfill4BB() BOX *pixSeedfill8BB() Just erase the c.c.: l_int32 pixSeedfill() l_int32 pixSeedfill4() l_int32 pixSeedfill8() Static stack helper functions for single raster line seedfill: static void pushFillsegBB() static void pushFillseg() static void popFillseg() The basic method in pixConnCompBB() is very simple. We scan the image in raster order, looking for the next ON pixel. When it is found, we erase it and every pixel of the 4- or 8-connected component to which it belongs, using Heckbert's seedfill algorithm. As pixels are erased, we keep track of the minimum rectangle that encloses all erased pixels; after the connected component has been erased, we save its bounding box in an array of boxes. When all pixels in the image have been erased, we have an array that describes every 4- or 8-connected component in terms of its bounding box. pixConnCompPixa() is a slight variation on pixConnCompBB(), where we additionally save an array of images (in a Pixa) of each of the 4- or 8-connected components. This is done trivially by maintaining two temporary images. We erase a component from one, and use the bounding box to extract the pixels within the b.b. from each of the two images. An XOR between these subimages gives the erased component. Then we erase the component from the second image using the XOR again, with the extracted component placed on the second image at the location of the bounding box. Rasterop does all the work. At the end, we have an array of the 4- or 8-connected components, as well as an array of the bounding boxes that describe where they came from in the original image. If you just want the number of connected components, pixCountConnComp() is a bit faster than pixConnCompBB(), because it doesn't have to keep track of the bounding rectangles for each c.c.
l_int32 nextOnPixelInRaster ( PIX *pixs, l_int32 xstart, l_int32 ystart, l_int32 *px, l_int32 *py )
nextOnPixelInRaster() Input: pixs (1 bpp) xstart, ystart (starting point for search) &x, &y (<return> coord value of next ON pixel) Return: 1 if a pixel is found; 0 otherwise or on error
BOXA * pixConnComp ( PIX *pixs, PIXA **ppixa, l_int32 connectivity )
pixConnComp() Input: pixs (1 bpp) &pixa (<optional return> pixa of each c.c.) connectivity (4 or 8) Return: boxa, or null on error Notes: (1) This is the top-level call for getting bounding boxes or a pixa of the components, and it can be used instead of either pixConnCompBB() or pixConnCompPixa(), rsp.
BOXA * pixConnCompBB ( PIX *pixs, l_int32 connectivity )
pixConnCompBB() Input: pixs (1 bpp) connectivity (4 or 8) Return: boxa, or null on error Notes: (1) Finds bounding boxes of 4- or 8-connected components in a binary image. (2) This works on a copy of the input pix. The c.c. are located in raster order and erased one at a time. In the process, the b.b. is computed and saved.
BOXA * pixConnCompPixa ( PIX *pixs, PIXA **ppixa, l_int32 connectivity )
pixConnCompPixa() Input: pixs (1 bpp) &pixa (<return> pixa of each c.c.) connectivity (4 or 8) Return: boxa, or null on error Notes: (1) This finds bounding boxes of 4- or 8-connected components in a binary image, and saves images of each c.c in a pixa array. (2) It sets up 2 temporary pix, and for each c.c. that is located in raster order, it erases the c.c. from one pix, then uses the b.b. to extract the c.c. from the two pix using an XOR, and finally erases the c.c. from the second pix. (3) A clone of the returned boxa (where all boxes in the array are clones) is inserted into the pixa. (4) If the input is valid, this always returns a boxa and a pixa. If pixs is empty, the boxa and pixa will be empty.
l_int32 pixCountConnComp ( PIX *pixs, l_int32 connectivity, l_int32 *pcount )
pixCountConnComp() Input: pixs (1 bpp) connectivity (4 or 8) &count (<return> Return: 0 if OK, 1 on error Notes: (1) This is the top-level call for getting the number of 4- or 8-connected components in a 1 bpp image. (2) It works on a copy of the input pix. The c.c. are located in raster order and erased one at a time.
l_int32 pixSeedfill ( PIX *pixs, L_STACK *stack, l_int32 x, l_int32 y, l_int32 connectivity )
pixSeedfill() Input: pixs (1 bpp) stack (for holding fillsegs) x,y (location of seed pixel) connectivity (4 or 8) Return: 0 if OK, 1 on error Notes: (1) This removes the component from pixs with a fg pixel at (x,y). (2) See pixSeedfill4() and pixSeedfill8() for details.
l_int32 pixSeedfill4 ( PIX *pixs, L_STACK *stack, l_int32 x, l_int32 y )
pixSeedfill4() Input: pixs (1 bpp) stack (for holding fillsegs) x,y (location of seed pixel) Return: 0 if OK, 1 on error Notes: (1) This is Paul Heckbert's stack-based 4-cc seedfill algorithm. (2) This operates on the input 1 bpp pix to remove the fg seed pixel, at (x,y), and all pixels that are 4-connected to it. The seed pixel at (x,y) must initially be ON. (3) Reference: see pixSeedFill4BB()
BOX * pixSeedfill4BB ( PIX *pixs, L_STACK *stack, l_int32 x, l_int32 y )
pixSeedfill4BB() Input: pixs (1 bpp) stack (for holding fillsegs) x,y (location of seed pixel) Return: box or null on error. Notes: (1) This is Paul Heckbert's stack-based 4-cc seedfill algorithm. (2) This operates on the input 1 bpp pix to remove the fg seed pixel, at (x,y), and all pixels that are 4-connected to it. The seed pixel at (x,y) must initially be ON. (3) Returns the bounding box of the erased 4-cc component. (4) Reference: see Paul Heckbert's stack-based seed fill algorithm in "Graphic Gems", ed. Andrew Glassner, Academic Press, 1990. The algorithm description is given on pp. 275-277; working C code is on pp. 721-722.) The code here follows Heckbert's exactly, except we use function calls instead of macros for pushing data on and popping data off the stack. This makes sense to do because Heckbert's fixed-size stack with macros is dangerous: images exist that will overrun the stack and crash. The stack utility here grows dynamically as needed, and the fillseg structures that are not in use are stored in another stack for reuse. It should be noted that the overhead in the function calls (vs. macros) is negligible.
l_int32 pixSeedfill8 ( PIX *pixs, L_STACK *stack, l_int32 x, l_int32 y )
pixSeedfill8() Input: pixs (1 bpp) stack (for holding fillsegs) x,y (location of seed pixel) Return: 0 if OK, 1 on error Notes: (1) This is Paul Heckbert's stack-based 8-cc seedfill algorithm. (2) This operates on the input 1 bpp pix to remove the fg seed pixel, at (x,y), and all pixels that are 8-connected to it. The seed pixel at (x,y) must initially be ON. (3) Reference: see pixSeedFill8BB()
BOX * pixSeedfill8BB ( PIX *pixs, L_STACK *stack, l_int32 x, l_int32 y )
pixSeedfill8BB() Input: pixs (1 bpp) stack (for holding fillsegs) x,y (location of seed pixel) Return: box or null on error. Notes: (1) This is Paul Heckbert's stack-based 8-cc seedfill algorithm. (2) This operates on the input 1 bpp pix to remove the fg seed pixel, at (x,y), and all pixels that are 8-connected to it. The seed pixel at (x,y) must initially be ON. (3) Returns the bounding box of the erased 8-cc component. (4) Reference: see Paul Heckbert's stack-based seed fill algorithm in "Graphic Gems", ed. Andrew Glassner, Academic Press, 1990. The algorithm description is given on pp. 275-277; working C code is on pp. 721-722.) The code here follows Heckbert's closely, except the leak checks are changed for 8 connectivity. See comments on pixSeedfill4BB() for more details.
BOX * pixSeedfillBB ( PIX *pixs, L_STACK *stack, l_int32 x, l_int32 y, l_int32 connectivity )
pixSeedfillBB() Input: pixs (1 bpp) stack (for holding fillsegs) x,y (location of seed pixel) connectivity (4 or 8) Return: box or null on error Notes: (1) This is the high-level interface to Paul Heckbert's stack-based seedfill algorithm.
Zakariyya Mughal <zmughal@cpan.org>
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.
To install Image::Leptonica, copy and paste the appropriate command in to your terminal.
cpanm
cpanm Image::Leptonica
CPAN shell
perl -MCPAN -e shell install Image::Leptonica
For more information on module installation, please visit the detailed CPAN module installation guide.