PNG和GIF透明度丢失了

Question

I am having a problem working with images and php.

I am using a function with which will resize an image according to my limitations and then create a new image.

The problem is when I have a png or gif file to resize, the transparency gets lost generating images with black background.

Here is the function:

// Resize image - preserve ratio of width and height.
function resizeImage($sourceImage, $targetImage, $maxWidth, $maxHeight, $quality = 70)
{
    // Obtain image from given source file.
    $info = getimagesize($sourceImage);
    $imgtype = image_type_to_mime_type($info[2]);

    switch ($imgtype) {
      case 'image/jpeg':
        $image = imagecreatefromjpeg($sourceImage);
      break;
      case 'image/png':
        $image = imagecreatefrompng($sourceImage);
      break;
      default:
        die('Invalid image type.');
    }

    // Get dimensions of source image.
    list($origWidth, $origHeight) = getimagesize($sourceImage);

    if ($maxWidth == 0)
    {
        $maxWidth  = $origWidth;
    }

    if ($maxHeight == 0)
    {
        $maxHeight = $origHeight;
    }

    // Calculate ratio of desired maximum sizes and original sizes.
    $widthRatio = $maxWidth / $origWidth;
    $heightRatio = $maxHeight / $origHeight;

    // Ratio used for calculating new image dimensions.
    $ratio = min($widthRatio, $heightRatio);

    // Calculate new image dimensions.
    $newWidth  = (int)$origWidth  * $ratio;
    $newHeight = (int)$origHeight * $ratio;

    // Create final image with new dimensions.
    $newImage = imagecreatetruecolor($newWidth, $newHeight);
    imagecopyresampled($newImage, $image, 0, 0, 0, 0, $newWidth, $newHeight, $origWidth, $origHeight);
    imagejpeg($newImage, $targetImage, $quality);

    // Free up the memory.
    imagedestroy($image);
    imagedestroy($newImage);

    return true;
}

Answer 1

You are always using imagejpeg no matter what extension you get, there is also imagepng and imagegif. You should use those if you have a .gif or .png

I'm talking about this line:

imagejpeg($newImage, $targetImage, $quality);

You should call imagejpeg, imagepng or imagegif depending the file type.