给定图像和纵横比的最大裁剪区域

Posted 2023-02-25

【中文标题】给定图像和纵横比的最大裁剪区域

【英文标题】：Max crop area for a given image and aspect ratio

【发布时间】：2011-12-16 23:28:21

【问题描述】：

是否有任何 php/GD 函数可以计算这个：

输入：图像宽度、图像高度和要遵守的纵横比。输出： 尊重给定纵横比的最大居中裁剪的宽度/高度 （尽管图像原始纵横比）。

示例：图片为 1000x500，a.r.为 1.25：最大裁剪为 625x500。图片为 100x110，最大裁剪为：80x110。

【参考方案1】：

没有计算这个的函数，因为它是初等数学：

$imageWidth = 1000;
$imageHeight = 500;
$ar = 1.25;

if ($ar < 1)  // "tall" crop
    $cropWidth = min($imageHeight * $ar, $imageWidth);
    $cropHeight = $cropWidth / $ar;

else  // "wide" or square crop
    $cropHeight = min($imageWidth / $ar, $imageHeight);
    $cropWidth = $cropHeight * $ar;

See it in action.

【讨论】：

谢谢。我花了几分钟的时间，得到了类似你的代码的东西（但你的解决方案更优雅）。是的，基本但有用。

非常好的解决方案。尽管当我试图理解它时我的大脑完全一片空白，但它就像一种魅力。

@ScooterDaraf：已修复。

【参考方案2】：

作为@Jon 的answer 的扩展，这是PHP-GD library 中这种方法的实现

/**
 * Crops image by taking largest area rectangle from center of image so that the desired aspect ratio is realized.
 * @param resource $src_image image resource to be cropped
 * @param float $required_aspect_ratio Desired aspect ratio to be achieved via cropping
 * @return resource cropped image
 */
public function withCenterCrop($src_image, float $required_aspect_ratio) 
    $crr_width = imagesx($src_image);
    $crr_height = imagesy($src_image);
    $crr_aspect_ratio = $crr_width / $crr_height;

    $cropped_image = null;
    if ($crr_aspect_ratio < $required_aspect_ratio) 
        // current image is 'taller' (than what we need), it must be trimmed off from top & bottom
        $new_width = $crr_width;
        $new_height = $new_width / $required_aspect_ratio;
        // calculate the value of 'y' so that central portion of image is cropped
        $crop_y = (int) (($crr_height - $new_height) / 2);
        $cropped_image = imagecrop(
            $src_image,
            ['x' => 0, 'y' => $crop_y, 'width' => $new_width, 'height' => $new_height]
        );
     else 
        // current image is 'wider' (than what we need), it must be trimmed off from sides
        $new_height = $crr_height;
        $new_width = $new_height * $required_aspect_ratio;
        // calculate the value of 'x' so that central portion of image is cropped
        $crop_x = (int) (($crr_width - $new_width) / 2);
        $cropped_image = imagecrop(
            $src_image,
            ['x' => $crop_x, 'y' => 0, 'width' => $new_width, 'height' => $new_height]
        );
    

    return $cropped_image;