php-gd如何实现图像边缘检测_php-gd图像边缘轮廓识别

function rgbToGray($r, $g, $b) {
    return intval(0.299 * $r + 0.587 * $g + 0.114 * $b);
}
<p>$image = imagecreatefromjpeg('input.jpg');
$width = imagesx($image);
$height = imagesy($image);</p><p>$grayImage = imagecreatetruecolor($width, $height);
for ($x = 0; $x < $width; $x++) {
for ($y = 0; $y < $height; $y++) {
$color = imagecolorat($image, $x, $y);
$r = ($color >> 16) & 0xFF;
$g = ($color >> 8) & 0xFF;
$b = $color & 0xFF;
$gray = rgbToGray($r, $g, $b);
$grayColor = imagecolorallocate($grayImage, $gray, $gray, $gray);
imagesetpixel($grayImage, $x, $y, $grayColor);
}
}</p>

<pre class="brush:php;toolbar:false;">$sobelImage = imagecreatetruecolor($width, $height);
$white = imagecolorallocate($sobelImage, 255, 255, 255);
imagefill($sobelImage, 0, 0, $white); // 背景白
<p>for ($x = 1; $x < $width - 1; $x++) {
for ($y = 1; $y < $height - 1; $y++) {
$gx = $gy = 0;</p><pre class="brush:php;toolbar:false;"><code>    // 3x3 邻域像素灰度值
    for ($i = -1; $i <= 1; $i++) {
        for ($j = -1; $j <= 1; $j++) {
            $pxColor = imagecolorat($grayImage, $x + $i, $y + $j);
            $gray = $pxColor & 0xFF;

            $gx += $gray * [ -1, 0, 1,
                            -2, 0, 2,
                            -1, 0, 1 ][($i+1)*3 + ($j+1)];
            $gy += $gray * [ -1,-2,-1,
                              0, 0, 0,
                              1, 2, 1 ][($i+1)*3 + ($j+1)];
        }
    }

    $magnitude = abs($gx) + abs($gy); // 梯度强度
    $edgeValue = $magnitude > 100 ? 0 : 255; // 设定阈值二值化

    $color = imagecolorallocate($sobelImage, $edgeValue, $edgeValue, $edgeValue);
    imagesetpixel($sobelImage, $x, $y, $color);
}

<pre class="brush:php;toolbar:false;">header('Content-Type: image/png');
imagepng($sobelImage);
<p>// 或保存
imagepng($sobelImage, 'edges.png');</p>

<pre class="brush:php;toolbar:false;">imagedestroy($image);
imagedestroy($grayImage);
imagedestroy($sobelImage);