Question

我有以下代码用于生成图像缩略图，但它仅适用于JPEG，原因不明，我无法弄清楚它为什么不能用于PNG？

function generate_image_thumbnail($source_image_path, $thumbnail_image_path)
    {
        list($source_image_width, $source_image_height, $source_image_type) = getimagesize($source_image_path);
        switch ($source_image_type) {
            case IMAGETYPE_GIF:
                $source_gd_image = imagecreatefromgif($source_image_path);
                break;
            case IMAGETYPE_JPEG:
                $source_gd_image = imagecreatefromjpeg($source_image_path);
                break;
            case IMAGETYPE_PNG:{
                $source_gd_image = imagecreatefrompng($source_image_path);
                break;
            }
        } //$source_image_type
        if ($source_gd_image === false) {
            return false;
        } //$source_gd_image === false
        $source_aspect_ratio    = $source_image_width / $source_image_height;
        $thumbnail_aspect_ratio = THUMBNAIL_IMAGE_MAX_WIDTH / THUMBNAIL_IMAGE_MAX_HEIGHT;
        if ($source_image_width <= THUMBNAIL_IMAGE_MAX_WIDTH && $source_image_height <= THUMBNAIL_IMAGE_MAX_HEIGHT) {
            $thumbnail_image_width  = $source_image_width;
            $thumbnail_image_height = $source_image_height;
        } //$source_image_width <= THUMBNAIL_IMAGE_MAX_WIDTH && $source_image_height <= THUMBNAIL_IMAGE_MAX_HEIGHT
        elseif ($thumbnail_aspect_ratio > $source_aspect_ratio) {
            $thumbnail_image_width  = (int) (THUMBNAIL_IMAGE_MAX_HEIGHT * $source_aspect_ratio);
            $thumbnail_image_height = THUMBNAIL_IMAGE_MAX_HEIGHT;
        } //$thumbnail_aspect_ratio > $source_aspect_ratio
        else {
            $thumbnail_image_width  = THUMBNAIL_IMAGE_MAX_WIDTH;
            $thumbnail_image_height = (int) (THUMBNAIL_IMAGE_MAX_WIDTH / $source_aspect_ratio);
        }
        $thumbnail_gd_image = imagecreatetruecolor($thumbnail_image_width, $thumbnail_image_height);
        imagecopyresampled($thumbnail_gd_image, $source_gd_image, 0, 0, 0, 0, $thumbnail_image_width, $thumbnail_image_height, $source_image_width, $source_image_height);

        switch ($source_image_type) {
            case IMAGETYPE_GIF:
                imagegif($thumbnail_gd_image, $thumbnail_image_path, 90);
                break;
            case IMAGETYPE_JPEG:
                imagejpeg($thumbnail_gd_image, $thumbnail_image_path, 90);
                break;
            case IMAGETYPE_PNG:{
                //imagealphablending($thumbnail_gd_image, false); 
                //imagesavealpha($thumbnail_gd_image,true);
                imagepng($thumbnail_gd_image, $thumbnail_image_path, 90);
                break;
            }
        }               



        imagedestroy($source_gd_image);
        imagedestroy($thumbnail_gd_image);
        return true;
    }

Answer 1

问题出现在第二个案例中，完全在

imagepng($thumbnail_gd_image, $thumbnail_image_path, 90);

根据imagepng函数

质量

Compression level: from 0 (no compression) to 9.

所以，将90改为9（例如）

imagepng($thumbnail_gd_image, $thumbnail_image_path, 9);

Answer 2

imagepng($thumbnail_gd_image, $thumbnail_image_path, 90);

应

imagepng($thumbnail_gd_image, $thumbnail_image_path, 9);

你可能已经开始工作了。但我想推荐php库imagemagick。如果您可以在webhost上访问它，那么在处理图像时它是非常好的库。您也可以下载该库以在本地使用它。

使用GD生成图像缩略图仅对PNG失败

2 个答案: