Step by Step solution about How to resolve the algorithm Canny edge detector step by step in the PHP programming language

This code takes an image as input and uses the RGBtoHSV function to convert each pixel's color from RGB to HSV. The HSV color space is used to detect edges in the image by comparing the hue of each pixel to the hue of the pixel below it. If the difference in hue is greater than 20, then an edge is detected and the pixel is set to red. Otherwise, the pixel is set to black. The resulting image is a grayscale image with the edges highlighted in red.

Here is a detailed explanation of the code:

1. The RGBtoHSV function takes three input parameters: r, g, and b, which represent the red, green, and blue components of a color in the range 0 to 255. The function converts the RGB values to the HSV color space, which is represented by three values:

   • h: Hue, which represents the color's dominant wavelength.
   • s: Saturation, which represents the purity of the color.
   • v: Value, which represents the brightness of the color.

2. The code then loads the image from the file specified by the $filename variable. The getimagesize function is used to get the width and height of the image, which are stored in the $w and $h variables, respectively.

3. The code then uses the imagecreatefrompng function to create a GD image resource from the loaded image.

4. The code then iterates over each pixel in the image, using two nested loops. The outer loop iterates over the rows of the image, and the inner loop iterates over the columns of the image.

5. For each pixel, the code uses the imagecolorat function to get the RGB color of the pixel. The RGB color is then converted to HSV using the RGBtoHSV function.

6. The code then compares the hue of the current pixel to the hue of the pixel below it. If the difference in hue is greater than 20, then an edge is detected.

7. If an edge is detected, the code uses the imagesetpixel function to set the color of the current pixel to red. Otherwise, the code sets the color of the current pixel to black.

8. After all of the pixels in the image have been processed, the code uses the header function to set the Content-Type of the response to image/jpeg. The imagepng function is then used to output the image to the browser. The imagedestroy function is finally used to destroy the GD image resource.

// input: r,g,b in range 0..255
function RGBtoHSV($r, $g, $b) {
	$r = $r/255.; // convert to range 0..1
	$g = $g/255.;
	$b = $b/255.;
	$cols = array("r" => $r, "g" => $g, "b" => $b);
	asort($cols, SORT_NUMERIC);
	$min = key(array_slice($cols, 1)); // "r", "g" or "b"
	$max = key(array_slice($cols, -1)); // "r", "g" or "b"

	// hue
	if($cols[$min] == $cols[$max]) {
		$h = 0;
	} else {
		if($max == "r") {
			$h = 60. * ( 0 + ( ($cols["g"]-$cols["b"]) / ($cols[$max]-$cols[$min]) ) );
		} elseif ($max == "g") {
			$h = 60. * ( 2 + ( ($cols["b"]-$cols["r"]) / ($cols[$max]-$cols[$min]) ) );
		} elseif ($max == "b") {
			$h = 60. * ( 4 + ( ($cols["r"]-$cols["g"]) / ($cols[$max]-$cols[$min]) ) );
		}
		if($h < 0) {
			$h += 360;
		}
	}

	// saturation
	if($cols[$max] == 0) {
		$s = 0;
	} else {
		$s = ( ($cols[$max]-$cols[$min])/$cols[$max] );
		$s = $s * 255;
	}

	// lightness
	$v = $cols[$max];
	$v = $v * 255;

	return(array($h, $s, $v));
}

$filename = "image.png";
$dimensions = getimagesize($filename);
$w = $dimensions[0]; // width
$h = $dimensions[1]; // height

$im = imagecreatefrompng($filename);

for($hi=0; $hi < $h; $hi++) {

	for($wi=0; $wi < $w; $wi++) {
		$rgb = imagecolorat($im, $wi, $hi);

		$r = ($rgb >> 16) & 0xFF;
		$g = ($rgb >> 8) & 0xFF;
		$b = $rgb & 0xFF;
		$hsv = RGBtoHSV($r, $g, $b);

		// compare pixel below with current pixel
		$brgb = imagecolorat($im, $wi, $hi+1);
		$br = ($brgb >> 16) & 0xFF;
		$bg = ($brgb >> 8) & 0xFF;
		$bb = $brgb & 0xFF;
		$bhsv = RGBtoHSV($br, $bg, $bb);

		// if difference in hue > 20, edge is detected
		if($hsv[2]-$bhsv[2] > 20) { 
                    imagesetpixel($im, $wi, $hi, imagecolorallocate($im, 255, 0, 0));
		} 
                else {
		    imagesetpixel($im, $wi, $hi, imagecolorallocate($im, 0, 0, 0));
		}
			
        }
        
}

header('Content-Type: image/jpeg');
imagepng($im);
imagedestroy($im);