php - PHP upscale an image?

Question

I am new to php and trying to learn about image upscaling. can you please show me how can I upscale an image to a certain size? For example, I would like to re-size the following image while keeping the aspect ratio. If this can be done, can you please show me with an example

Answer 1

$source_image = imagecreatefromjpeg("osaka.jpg");
$source_imagex = imagesx($source_image);
$source_imagey = imagesy($source_image);
$dest_imagex = 300;
$dest_imagey = 200;
$dest_image = imagecreatetruecolor($dest_imagex, $dest_imagey);

质量差，但速度快：

imagecopyresized($dest_image, $source_image, 0, 0, 0, 0, 
            $dest_imagex, $dest_imagey, $source_imagex, $source_imagey);

最好的质量，但速度慢：

imagecopyresampled($dest_image, $source_image, 0, 0, 0, 0, 
            $dest_imagex, $dest_imagey, $source_imagex, $source_imagey);

Answer 2

您可以通过将一侧设置为自定义长度并将另一侧设置为“自动”来放大 html/CSS 中的图像。无需在 php 中对其进行升级，因为升级后的图像不包含比“正常”版本更多的信息。它只会消耗更多的带宽。

<img src="http://placekitten.com/50/50" style="width: 50px; height: auto;" />

<img src="http://placekitten.com/50/50" style="width: 200px; height: auto;" />

看到这个小提琴。

Answer 3

如果你真的想用 PHP 来做，你可以看看“imagecopyresampled”函数：

php.net 上的 imagecopyresampled 示例

但是如果你想保持比例，你必须计算它并手动应用到宽度和高度。

Answer 4

图像放大

// creating image resource from image path (also supports url)
$source_image = imagecreatefromjpeg($destinationReal); // 1150x235 px

// getting source image dimension
$source_imagex = imagesx($source_image);
$source_imagey = imagesy($source_image);

// set new image dimension
$dest_imagex = 1150;
$dest_imagey = 348; // in my case I only upscale the height

// create image (in memory)
$dest_image = imagecreatetruecolor($dest_imagex, $dest_imagey);
imagecopyresampled($dest_image, $source_image, 0, 0, 0, 0,
                $dest_imagex, $dest_imagey, $source_imagex, $source_imagey);

// save new image
imagejpeg($dest_image, $destination);