This picture become blurry after resizing

Question

After uploading and resizing this photo, i noticed the quality of it become slightly blurry... why does this happen? I have enough space so what else could be the problem?

original,

after resizing,

But other pictures that I uploaded have no problem at all. Why does it happen to this picture only?

Would it be caused by the resizing function below?

function resize_image($image,$width,$height,$scale) 
{
    # Calculating proportionality
    list($imagewidth, $imageheight, $imageType) = getimagesize($image);
    $imageType = image_type_to_mime_type($imageType);
    $newImageWidth = ceil($width * $scale);
    $newImageHeight = ceil($height * $scale);
    $newImage = imagecreatetruecolor($newImageWidth,$newImageHeight);

    # Loading image to memory according to type
    switch($imageType) 
    {
        case "image/gif":
            $source = imagecreatefromgif($image); 
            break;
        case "image/pjpeg":
        case "image/jpeg":
        case "image/jpg":
            $source = imagecreatefromjpeg($image); 
            break;
        case "image/png":
        case "image/x-png":
            $source = imagecreatefrompng($image); 
            break;
    }

    # This is the resizing/resampling/transparency-preserving magic
    if ( ($imageType == "image/gif") || ($imageType == "image/png") ) 
    {
        $transIndex = imagecolortransparent($source);

        if($transIndex >= 0) 
        {
            $transcol = imagecolorsforindex($source, $transIndex);
            $transIndex = imagecolorallocatealpha($newImage, $transcol['red'], $transcol['green'], $transcol['blue'], 127);
            imagefill($newImage, 0, 0, $transIndex);
            imagecolortransparent($newImage, $transIndex);
        }

        elseif ($imageType == "image/png" || $imageType == "image/x-png") 
        {
            imagealphablending($newImage, false);
            $color = imagecolorallocatealpha($newImage, 0, 0, 0, 127);
            imagefill($newImage, 0, 0, $color);
            imagesavealpha($newImage, true);
        }
    }

    imagecopyresampled($newImage,$source,0,0,0,0,$newImageWidth,$newImageHeight,$width,$height);

    # Writing image according to type to the output destination
    switch($imageType) 
    {
        case "image/gif":
            imagegif($newImage,$image); 
            break;
        case "image/pjpeg":
        case "image/jpeg":
        case "image/jpg":
            imagejpeg($newImage,$image,90); 
            break;
        case "image/png":
        case "image/x-png":
            imagepng($newImage,$image);  
            break;
    }

    chmod($image, 0777);
    return $image;
}

Answer 1

Jpeg is a format which is optimized for compressing photographies. In images such as the ones you show, the artifacts are far more noticeable than normal. I suggest you change the quality level on this line:

imagejpeg($newImage,$image,100);

Another option would be to save the image in png.