Image::Leptonica::Func::edge
version 0.04
edge.c
edge.c Sobel edge detecting filter PIX *pixSobelEdgeFilter() Two-sided edge gradient filter PIX *pixTwoSidedEdgeFilter() Measurement of edge smoothness l_int32 pixMeasureEdgeSmoothness() NUMA *pixGetEdgeProfile() l_int32 pixGetLastOffPixelInRun() l_int32 pixGetLastOnPixelInRun() The Sobel edge detector uses these two simple gradient filters. 1 2 1 1 0 -1 0 0 0 2 0 -2 -1 -2 -1 1 0 -1 (horizontal) (vertical) To use both the vertical and horizontal filters, set the orientation flag to L_ALL_EDGES; this sums the abs. value of their outputs, clipped to 255. See comments below for displaying the resulting image with the edges dark, both for 8 bpp and 1 bpp.
NUMA * pixGetEdgeProfile ( PIX *pixs, l_int32 side, const char *debugfile )
pixGetEdgeProfile() Input: pixs (1 bpp) side (L_FROM_LEFT, L_FROM_RIGHT, L_FROM_TOP, L_FROM_BOT) debugfile (<optional> displays constructed edge; use NULL for no output) Return: na (of fg edge pixel locations), or null on error
l_int32 pixGetLastOffPixelInRun ( PIX *pixs, l_int32 x, l_int32 y, l_int32 direction, l_int32 *ploc )
pixGetLastOffPixelInRun() Input: pixs (1 bpp) x, y (starting location) direction (L_FROM_LEFT, L_FROM_RIGHT, L_FROM_TOP, L_FROM_BOT) &loc (<return> location in scan direction coordinate of last OFF pixel found) Return: na (of fg edge pixel locations), or null on error Notes: (1) Search starts from the pixel at (x, y), which is OFF. (2) It returns the location in the scan direction of the last pixel in the current run that is OFF. (3) The interface for these pixel run functions is cleaner when you ask for the last pixel in the current run, rather than the first pixel of opposite polarity that is found, because the current run may go to the edge of the image, in which case no pixel of opposite polarity is found.
l_int32 pixGetLastOnPixelInRun ( PIX *pixs, l_int32 x, l_int32 y, l_int32 direction, l_int32 *ploc )
pixGetLastOnPixelInRun() Input: pixs (1 bpp) x, y (starting location) direction (L_FROM_LEFT, L_FROM_RIGHT, L_FROM_TOP, L_FROM_BOT) &loc (<return> location in scan direction coordinate of first ON pixel found) Return: na (of fg edge pixel locations), or null on error Notes: (1) Search starts from the pixel at (x, y), which is ON. (2) It returns the location in the scan direction of the last pixel in the current run that is ON.
l_int32 pixMeasureEdgeSmoothness ( PIX *pixs, l_int32 side, l_int32 minjump, l_int32 minreversal, l_float32 *pjpl, l_float32 *pjspl, l_float32 *prpl, const char *debugfile )
pixMeasureEdgeSmoothness() Input: pixs (1 bpp) side (L_FROM_LEFT, L_FROM_RIGHT, L_FROM_TOP, L_FROM_BOT) minjump (minimum jump to be counted; >= 1) minreversal (minimum reversal size for new peak or valley) &jpl (<optional return> jumps/length: number of jumps, normalized to length of component side) &jspl (<optional return> jumpsum/length: sum of all sufficiently large jumps, normalized to length of component side) &rpl (<optional return> reversals/length: number of peak-to-valley or valley-to-peak reversals, normalized to length of component side) debugfile (<optional> displays constructed edge; use NULL for no output) Return: 0 if OK, 1 on error Notes: (1) This computes three measures of smoothness of the edge of a connected component: * jumps/length: (jpl) the number of jumps of size >= @minjump, normalized to the length of the side * jump sum/length: (jspl) the sum of all jump lengths of size >= @minjump, normalized to the length of the side * reversals/length: (rpl) the number of peak <--> valley reversals, using @minreverse as a minimum deviation of the peak or valley from its preceeding extremum, normalized to the length of the side (2) The input pix should be a single connected component, but this is not required.
PIX * pixSobelEdgeFilter ( PIX *pixs, l_int32 orientflag )
pixSobelEdgeFilter() Input: pixs (8 bpp; no colormap) orientflag (L_HORIZONTAL_EDGES, L_VERTICAL_EDGES, L_ALL_EDGES) Return: pixd (8 bpp, edges are brighter), or null on error Notes: (1) Invert pixd to see larger gradients as darker (grayscale). (2) To generate a binary image of the edges, threshold the result using pixThresholdToBinary(). If the high edge values are to be fg (1), invert after running pixThresholdToBinary(). (3) Label the pixels as follows: 1 4 7 2 5 8 3 6 9 Read the data incrementally across the image and unroll the loop. (4) This runs at about 45 Mpix/sec on a 3 GHz processor.
PIX * pixTwoSidedEdgeFilter ( PIX *pixs, l_int32 orientflag )
pixTwoSidedEdgeFilter() Input: pixs (8 bpp; no colormap) orientflag (L_HORIZONTAL_EDGES, L_VERTICAL_EDGES) Return: pixd (8 bpp, edges are brighter), or null on error Notes: (1) For detecting vertical edges, this considers the difference of the central pixel from those on the left and right. For situations where the gradient is the same sign on both sides, this computes and stores the minimum (absolute value of the) difference. The reason for checking the sign is that we are looking for pixels within a transition. By contrast, for single pixel noise, the pixel value is either larger than or smaller than its neighbors, so the gradient would change direction on each side. Horizontal edges are handled similarly, looking for vertical gradients. (2) To generate a binary image of the edges, threshold the result using pixThresholdToBinary(). If the high edge values are to be fg (1), invert after running pixThresholdToBinary(). (3) This runs at about 60 Mpix/sec on a 3 GHz processor. It is about 30% faster than Sobel, and the results are similar.
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.