Language agnostic 按比例调整图像大小

我在将图像缩放到适当的预定义大小时遇到了一点问题。我想知道——因为这纯粹是数学，是否有某种通用的逻辑算法在每种语言（PHP、ActionScript、Javascript等）中都能按比例缩放图像

我现在正在使用这个：

var maxHeight   = 300;
var maxWidth    = 300;

var ratio:Number    =   height / width;

if (height > maxHeight) {
    height = maxHeight;
    width = Math.round(height / ratio);
} 

else if(width > maxWidth) {
    width = maxWidth;
    height = Math.round(width * ratio);
}

---

但它不能正常工作。当然，图像按比例缩放，但大小没有设置为300（宽度或高度）。这有点道理，但我想知道是否有一种简单易行的方法可以按比例缩放图像。

我建议不要自己编写这段代码；有无数像素级的细节需要花很长时间才能正确处理。使用ImageMagick，它是最好的图形库

ratio = MIN( maxWidth / width, maxHeight/ height );
width = ratio * width;
height = ratio * height;

---

确保所有除法都是浮点值。

Dark Shikari拥有它。问题中所述的解决方案失败了，因为您没有首先确定哪个dimenson的大小与最大大小之比更大，然后再将两个维度都减少该更大的比例

您当前的解决方案使用一个潜在维度冲突的串行条件分析，然后使用另一个将不起作用

---

另外请注意，如果您想放大图像，您当前的解决方案将无法运行，而Dark Shikari的解决方案将再次运行。

这是我为我的站点开发的一个功能，您可能需要使用。这是基于你上面的答案

它不仅做图像处理，还做其他事情-请删除所有不必要的东西

<?php

$thumb_width    = 500;
$thumb_height   = 500;

if ($handle = opendir('to-do')) {
    echo "Directory handle: $handle<br />";
    echo "Files:<br /><br />";

    /* This is the correct way to loop over the directory. */
    while (false !== ($file = readdir($handle))) {

        if ( ($file != ".") && ($file != "..") ){
            echo "$file";

            $original_path = "to-do/" . $file;

            $source_image = ImageCreateFromJPEG( $original_path );
            $thumb_width = $thumb_width;
            $thumb_height = $thumb_height;

            // Create the image, of the required size
            $thumbnail = imagecreatetruecolor($thumb_width, $thumb_height);
            if($thumbnail === false) {
                //creation failed -- probably not enough memory
                return null;
            }

            // Fill the image with a white color (this will be visible in the padding around the image,
            // if the aspect ratios of the image and the thumbnail do not match)
            // Replace this with any color you want, or comment it out for black.
            // I used grey for testing =)
            $fill = imagecolorallocate($thumbnail, 255, 255, 255);
            imagefill($thumbnail, 0, 0, $fill);

            // Compute resize ratio
            $hratio = $thumb_height / imagesy($source_image);
            $wratio = $thumb_width / imagesx($source_image);
            $ratio = min($hratio, $wratio);

            // If the source is smaller than the thumbnail size, 
            // Don't resize -- add a margin instead
            // (that is, dont magnify images)
            if ($ratio > 1.0)
                $ratio = 1.0;

            // Compute sizes
            $sy = floor(imagesy($source_image) * $ratio);
            $sx = floor(imagesx($source_image) * $ratio);

            // Compute margins
            // Using these margins centers the image in the thumbnail.
            // If you always want the image to the top left, set both of these to 0
            $m_y = floor(($thumb_height - $sy) / 2);
            $m_x = floor(($thumb_width - $sx) / 2);

            // Copy the image data, and resample
            // If you want a fast and ugly thumbnail, replace imagecopyresampled with imagecopyresized
            if (!imagecopyresampled($thumbnail, $source_image,
                $m_x, $m_y, //dest x, y (margins)
                0, 0, //src x, y (0,0 means top left)
                $sx, $sy,//dest w, h (resample to this size (computed above)
                imagesx($source_image), imagesy($source_image)) //src w, h (the full size of the original)
            ) {
                //copy failed
                imagedestroy($thumbnail);
                return null;
            }

            /* Set the new file name */
            $thumbnail_file_name = $file;

            /* Apply changes on the original image and write the result on the disk */
            ImageJPEG( $thumbnail, $complete_path . "done/" . $thumbnail_file_name );
            unset($source_image);
            unset($thumbnail);
            unset($original_path);
            unset($targeted_image_size);

            echo " done<br />";

        }

    }

    closedir($handle);
}

?>

---

我将此函数设置为按比例缩放，它使用给定的宽度、高度，以及您想要的最大宽度/高度（取决于给定的宽度和高度）

用法：

            $getScale = scaleProportional(600,200,500);
            $targ_w = $getScale['width']; //returns 500
            $targ_h = $getScale['height']; //returns 16,6666667

我是这样做的：

+ (NSSize) scaleHeight:(NSSize)origSize 
             newHeight:(CGFloat)height {

    NSSize newSize = NSZeroSize;
    if ( origSize.height == 0 ) return newSize;

    newSize.height = height;
    CGFloat factor = ( height / origSize.height );
    newSize.width  = (origSize.width * factor );

    return newSize;
}

+ (NSSize) scaleWidth:(NSSize)origSize 
             newWidth:(CGFloat)width {

    NSSize newSize = NSZeroSize;
    if ( origSize.width == 0 ) return newSize;

    newSize.width  = width;
    CGFloat factor = ( width / origSize.width );
    newSize.height = (origSize.height * factor );

    return newSize;
}

所以，请记住，它必须被清洁，有可移动部分负载。
+ (NSSize) scaleHeight:(NSSize)origSize 
             newHeight:(CGFloat)height {

    NSSize newSize = NSZeroSize;
    if ( origSize.height == 0 ) return newSize;

    newSize.height = height;
    CGFloat factor = ( height / origSize.height );
    newSize.width  = (origSize.width * factor );

    return newSize;
}

+ (NSSize) scaleWidth:(NSSize)origSize 
             newWidth:(CGFloat)width {

    NSSize newSize = NSZeroSize;
    if ( origSize.width == 0 ) return newSize;

    newSize.width  = width;
    CGFloat factor = ( width / origSize.width );
    newSize.height = (origSize.height * factor );

    return newSize;
}