php - 图像调整大小 : Poor jpeg quality and black PNG backgrounds

Question

最后:我决定基本上使用这个:http://shiftingpixel.com/2008/03/03/smart-image-resizer/

因为它处理所有事情，我关闭了缓存并在管理 Controller 中执行此操作:

    $image = file_get_contents(SITE_ADMIN_IMAGE.'/SmartImage.php?width='.$this->thumb_width.'&height='.$this->thumb_height.'&image=/images/'.$this->image_directory.'/'.$formData['image_url'].'');
    file_put_contents(ROOT_PATH.'/public/images/'.$this->image_directory.'/thumb/'.$formData['image_url'], $image);

编辑:我发现这可行，但它会产生非常锐利的边缘，看起来不对。

    imagecolortransparent($dstImage, $background);
    imagealphablending($dstImage, false);
    $colorTransparent = imagecolorallocatealpha($dstImage, 0, 0, 0, 127);
    imagefill($dstImage, 0, 0, $colorTransparent);
    imagesavealpha($dstImage, true);
    imagepng($dstImage, $toWhere);

想法？

你好，

我的类(class)有两个问题，基本上 jpeg 图像的质量很差，但我不确定这是否与我的比例调整有关。理想情况下，我希望这门课对图像尺寸有严格要求并对其进行裁剪，但我无法理解它。

我的主要问题是 png 总是有黑色背景，有没有人遇到过这种情况？

<?php


    class OpenSource_ImageResize {


        function __construct($theFile, $toWhere, $mime, $extension, $newWidth, $newHeight) {

            if ($mime == NULL) {
                $mime = getimagesize($theFile);
                $mime = $mime['mime'];
            }


            if ($mime == 'image/jpeg') {
                $size = getimagesize($theFile);

                if ($size[0] > $newWidth || $size[1] > $newHeight) {
                    $sourceImage = imagecreatefromjpeg($theFile);
                } else {
                    return copy($theFile, $toWhere);
                    throw new exception('Could not create jpeg');
                    return false;
                }
            } else if ($mime == 'image/png') {
                $size = getimagesize($theFile);

                if ($size[0] > $newWidth || $size[1] > $newHeight) {
                    $sourceImage = imagecreatefrompng($theFile);
                } else {
                    return copy($theFile, $toWhere);
                    //throw new exception('Could not create png');
                    return false;
                }
            } else if ($mime == 'image/gif') {
                $size = getimagesize($theFile);

                if ($size[0] > $newWidth || $size[1] > $newHeight) {
                    $sourceImage = imagecreatefromgif ($theFile);
                } else {
                    return copy($theFile, $toWhere);
                    //throw new exception('Could not create gif');
                    return false;
                }
            } else {
                throw new exception('Not a valid mime type');
                return false;
            }

                $oldX = imageSX($sourceImage); 
                $oldY = imageSY($sourceImage); 

                if ($newWidth == NULL) {
                    $thumbHeight = $newHeight;
                    $thumbWidth = round($newHeight/($oldY/$oldX));
                } else 

                if ($oldX > $oldY) {
                    $thumbWidth = $newWidth; 
                    $thumbHeight = $oldY * ($newHeight/$oldX);
                } 

                if ($oldX < $oldY) {
                    $thumbWidth = round($newHeight/($oldY/$oldX));
                    $thumbHeight = $newHeight;
                }

                if ($oldX == $oldY) {
                    $thumbWidth = $newWidth; 
                    $thumbHeight = $newHeight;
                }

                    if (!gd_info()) {
                        $dstImage = ImageCreate($thumbWidth, $thumbHeight); 
                        imagecopyresized($dstImage, $sourceImage, 0, 0, 0, 0, $thumbWidth, $thumbHeight, $oldX, $oldY);
                    } else {
                        $dstImage = ImageCreateTrueColor($thumbWidth, $thumbHeight); 
                        imagecopyresampled($dstImage, $sourceImage, 0, 0, 0, 0, $thumbWidth, $thumbHeight, $oldX, $oldY);
                    } 

                    if ($mime == 'image/png') {
                        $xparent = imagecolorresolvealpha($dstImage, 255,2,240, 0) ;
                        imagecolortransparent($dstImage,$xparent);
                        imagealphablending($dstImage,true);
                        imagepng($dstImage, $toWhere);

                    } else if ($mime == 'image/jpeg') { 
                        imagejpeg($dstImage, $toWhere);

                    } else if ($mime == 'image/gif') {
                        imagegif ($dstImage, $toWhere);

                    }

                    imagedestroy($dstImage); 
                    imagedestroy($sourceImage);
                    return true;
        }

}

Answer 1

关于 JPEG 图像质量，您需要使用 imagejpeg() 中的第三个参数。 :

imagejpeg($dstImage, $toWhere, 90); // any value above 85 should be fine

关于 PNG 透明度，你做错了。您的脚本很糟糕并且存在根本性问题，我会给您留下一个修改后的脚本来解决您的两个问题。它仍然可以进一步优化，但我选择留下一些你原来不太重要的错误，这样你就不会感到迷茫:

class OpenSource_ImageResize
{
    // $extension is not used?
    function __construct($theFile, $toWhere, $mime, $extension, $newWidth, $newHeight)
    {
        $sourceImage = ImageCreateFromString(file_get_contents($theFile));

        if (is_resource($sourceImage))
        {
            $info = getimagesize($theFile);

            if (is_null($mime))
            {
                $mime = $info['mime'];
            }

            if ($info[0] <= $newWidth && $info[1] <= $newHeight)
            {
                imagedestroy($sourceImage);
                return copy($theFile, $toWhere);
            }

            if (is_null($newWidth))
            {
                $thumbHeight = $newHeight;
                $thumbWidth = round($newHeight/($info[1]/$info[0]));
            }

            else if ($info[0] > $info[1])
            {
                $thumbWidth = $newWidth;
                $thumbHeight = $info[1] * ($newHeight/$info[0]);
            }

            if ($info[0] < $info[1])
            {
                $thumbWidth = round($newHeight/($info[1]/$info[0]));
                $thumbHeight = $newHeight;
            }

            if ($info[0] == $info[1])
            {
                $thumbWidth = $newWidth;
                $thumbHeight = $newHeight;
            }

            $dstImage = ImageCreateTrueColor($thumbWidth, $thumbHeight);

            /* fix PNG transparency issues */           
            ImageFill($dstImage, 0, 0, IMG_COLOR_TRANSPARENT);
            ImageSaveAlpha($dstImage, true);
            ImageAlphaBlending($dstImage, true);

            imagecopyresampled($dstImage, $sourceImage, 0, 0, 0, 0, $thumbWidth, $thumbHeight, $info[0], $info[1]);

            switch ($mime)
            {
                case 'image/png':
                    imagepng($dstImage, $toWhere, 9); // compress it (level 1 to 9)
                break;

                case 'image/jpeg':
                    imagejpeg($dstImage, $toWhere, 90); // quality = 90 (1 to 100, default is "about" 75)
                break;

                case 'image/gif':
                    imagegif($dstImage, $toWhere);
                break;
            }

            imagedestroy($dstImage);
            imagedestroy($sourceImage);

            return true;
        }
    }
}

很抱歉没有明确指出您的错误，但错误太多了，现在是凌晨 3 点，需要睡一觉 - 学习它并阅读手册，如果您有任何疑问，请告诉我。