PHP和GD库教程：如何给图片添加怀旧效果

<?php
//指定图片路径
$imagePath = 'path_to_your_image.jpg';

//创建一个图像资源
$image = imagecreatefromjpeg($imagePath);

//获取图像的宽度和高度
$width = imagesx($image);
$height = imagesy($image);

//将图像转换为灰度图像
imagefilter($image, IMG_FILTER_GRAYSCALE);

//对每个像素进行亮度调整
for ($x = 0; $x < $width; $x++) {
    for ($y = 0; $y < $height; $y++) {
        $rgb = imagecolorat($image, $x, $y);
        $red = ($rgb >> 16) & 0xFF;
        $green = ($rgb >> 8) & 0xFF;
        $blue = $rgb & 0xFF;
        $y = ($red + $green + $blue) / 3;
        imagecolorset($image, $rgb, $y, $y, $y);
    }
}

//对每个像素进行色调调整
for ($x = 0; $x < $width; $x++) {
    for ($y = 0; $y < $height; $y++) {
        $rgb = imagecolorat($image, $x, $y);
        $red = ($rgb >> 16) & 0xFF;
        $green = ($rgb >> 8) & 0xFF;
        $blue = $rgb & 0xFF;
        $red = min(255, max(0, $red - 30)); //减少红色通道的值
        $green = min(255, max(0, $green - 20)); //减少绿色通道的值
        $blue = min(255, max(0, $blue + 10)); //增加蓝色通道的值
        $rgb = ($red << 16) | ($green << 8) | $blue;
        imagesetpixel($image, $x, $y, $rgb);
    }
}

//对每个像素进行饱和度调整
for ($x = 0; $x < $width; $x++) {
    for ($y = 0; $y < $height; $y++) {
        $rgb = imagecolorat($image, $x, $y);
        $red = ($rgb >> 16) & 0xFF;
        $green = ($rgb >> 8) & 0xFF;
        $blue = $rgb & 0xFF;
        $max = max($red, $green, $blue);
        $min = min($red, $green, $blue);
        $avg = ($max + $min) / 2;
        $red = min(255, max(0, $avg + 10)); //增加红色通道的值
        $green = min(255, max(0, $avg + 5)); //增加绿色通道的值
        $blue = min(255, max(0, $avg)); //保持蓝色通道不变
        $rgb = ($red << 16) | ($green << 8) | $blue;
        imagesetpixel($image, $x, $y, $rgb);
    }
}

//输出图像
header('Content-type: image/jpeg');
imagejpeg($image);

//释放图像资源
imagedestroy($image);
?>