Perform hough line detection (Generally named Hough Transform) on an input image

samples/hough_lines_detection.c

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+/*
+ * Programming introduction with the SOD Embedded Image Processing API.
+ * Copyright (C) PixLab | Symisc Systems, https://sod.pixlab.io
+ */
+/*
+* Compile this file together with the SOD embedded source code to generate
+* the executable. For example:
+*
+*  gcc sod.c hough_lines_detection.c -lm -Ofast -march=native -Wall -std=c99 -o sod_img_proc
+*  
+* Under Microsoft Visual Studio (>= 2015), just drop `sod.c` and its accompanying
+* header files on your source tree and you're done. If you have any trouble
+* integrating SOD in your project, please submit a support request at:
+* https://sod.pixlab.io/support.html
+*/
+/*
+* This simple program is a quick introduction on how to embed and start
+* experimenting with SOD without having to do a lot of tedious
+* reading and configuration.
+*
+* Make sure you have the latest release of SOD from:
+*  https://pixlab.io/downloads
+* The SOD Embedded C/C++ documentation is available at:
+*  https://sod.pixlab.io/api.html
+*/
+#include <stdio.h>
+#include "sod.h"
+/*
+ * Perform hough line detection (Generally named Hough Transform) on an input image.
+ */
+int main(int argc, char *argv[])
+{
+	/* Input image (pass a path or use the test image shipped with the samples ZIP archive) */
+	const char *zInput = argc > 1 ? argv[1] : "./test.png";
+	/* Processed output image path */
+	const char *zOut = argc > 2 ? argv[2] : "./out_lines.png";
+	/* Load the input image in the grayscale colorspace */
+	sod_img imgIn = sod_img_load_grayscale(zInput);
+	if (imgIn.data == 0) {
+		/* Invalid path, unsupported format, memory failure, etc. */
+		puts("Cannot load input image..exiting");
+		return 0;
+	}
+	/* A full color copy of the input image so we can draw later rose lines on it.
+	 */
+	sod_img imgCopy = sod_img_load_color(zInput);
+	/* 
+	 * Perform Canny edge detection first which is a mandatory step */
+	sod_img cannyImg = sod_canny_edge_image(imgIn, 0);
+	/*
+	 * Each detected line is represented by an instance of the `sod_pts`
+	 * structure returned as an array by the Hough interface where
+	 * each entry of this array (i and i + 1) hold the starting and 
+	 * ending position (x_start, y_start, x_end, y_end) for each line.
+	 */
+	sod_pts * aLines;
+	int i, nPts, nLines;
+	/* Perform hough line detection on the canny edged image
+	 * Depending on the analyzed image/frame, you should experiment
+	 * with different thresholds for best results.
+	 */
+	aLines = sod_hough_lines_detect(cannyImg, 0 /* default threshold which may not good for all images */, &nPts);
+	/* Report */
+	nLines = nPts / 2;
+	printf("%d line(s) were detected\n", nLines);
+	/* Draw a rose line for each entry on the full color image copy */
+	for (i = 0; i < nLines; i += 2) {
+		sod_image_draw_line(imgCopy, aLines[i], aLines[i + 1], 255, 0, 255);
+	}
+	/* Finally save the output image to the specified path */
+	sod_img_save_as_png(imgCopy, zOut);
+	/* Cleanup */
+	sod_hough_lines_release(aLines);
+	sod_free_image(imgIn);
+	sod_free_image(cannyImg);
+	sod_free_image(imgCopy);
+	return 0;
+}