Question

我将用户上传的图像重新调整为特定尺寸（即特定宽度和高度）。我想制作尺寸 940 px * 370 px 的上传图片。但在这样做的同时，我并不想影响用户最初上传的图像质量。

我的代码所面临的问题是图像尺寸已缩小到指定尺寸，但图像质量受到严重影响。上传的图片正在缩小。

我没有得到如何保持上传图片质量的完整性

为了实现此功能，我已经编写了以下代码。

HTML代码：

<html>
  <body>
    <form action="upload_file.php" method="post" enctype="multipart/form-data">
      <label for="file">Filename:</label>
      <input type="file" name="file" id="file"><br>
      <input type="submit" name="submit" value="Submit">
    </form>
  </body>
</html>

PHP代码：

<?php
  $allowedExts = array("gif", "jpeg", "jpg", "png");
  $temp = explode(".", $_FILES["file"]["name"]);
  $extension = end($temp);

  if ((($_FILES["file"]["type"] == "image/gif")
    || ($_FILES["file"]["type"] == "image/jpeg")
    || ($_FILES["file"]["type"] == "image/jpg")
    || ($_FILES["file"]["type"] == "image/pjpeg")
    || ($_FILES["file"]["type"] == "image/x-png")
    || ($_FILES["file"]["type"] == "image/png"))
    && ($_FILES["file"]["size"] < 5242880)
    && in_array($extension, $allowedExts)) {
      if ($_FILES["file"]["error"] > 0) {
        echo "Return Code: " . $_FILES["file"]["error"] . "<br>";
      } else {
        echo "Upload: " . $_FILES["file"]["name"] . "<br>";
        echo "Type: " . $_FILES["file"]["type"] . "<br>";
        echo "Size: " . ($_FILES["file"]["size"] / 1024) . " kB<br>";
        echo "Temp file: " . $_FILES["file"]["tmp_name"] . "<br>";
        if (file_exists("upload/" . $_FILES["file"]["name"])) {
          echo $_FILES["file"]["name"] . " already exists. ";
        } else {
          //move_uploaded_file($_FILES["file"]["tmp_name"], "upload/" . $_FILES["file"]["name"]);

          //Store the name of the temporary copy of the file stored on the server
          $images = $_FILES["file"]["tmp_name"];         

          /*Create a new file name for uploaded image file :
           *prepend the string "upload" to it's original file name
          */
          $new_images = "upload".$_FILES["file"]["name"];

          //Copies a file contents from one file to another
          //copy($_FILES["file"]["tmp_name"],"upload/".$_FILES["file"]["name"]);

          $width = 940;

          //Determine the size of a given image file and return the dimensions along with the file type 
          $size=GetimageSize($images);

          //$height=round($width*$size[1]/$size[0]);

          $height = 370;

          //Create a new image from file or URL & returns an image identifier representing the image obtained from the given filename.
          $images_orig = ImageCreateFromJPEG($images);

          //Get image width of originally uploaded image
          $photoX = ImagesX($images_orig);

          //Get image height of originally uploaded image
          $photoY = ImagesY($images_orig);

          //Create a new true color image & returns an image identifier representing a black image of the specified size.
          $images_fin = ImageCreateTrueColor($width, $height);

          /*Copy and resize part of an image with resampling
           *copies a rectangular portion of one image to another image, 
           *smoothly interpolating pixel values so that, in particular, 
           *reducing the size of an image still retains a great deal of clarity. 
          */
          ImageCopyResampled($images_fin, $images_orig, 0, 0, 0, 0, $width+1, $height+1, $photoX, $photoY);

          /*Output image to browser or file
           *creates a JPEG file from the given image.
          */  
          ImageJPEG($images_fin,"upload/".$new_images);

          /*Destroy an image
           *frees any memory associated with image image.  
          */
          ImageDestroy($images_orig);
          ImageDestroy($images_fin);

          echo "Stored in: " . "upload/" . $_FILES["file"]["name"];
        }
      }
    } else {
      echo "Invalid file";
    }
?>

如果有人能在这方面帮助我，对我来说会非常有帮助。

提前致谢。

为了更清楚地了解我面临的问题，我正在使用PHP代码附加原始图像和修改后的图像：

原始图片如下： enter image description here

上传服务器后的图像（即受影响的图像）如下： enter image description here

Answer 1

您应该缩放图像以保持纵横比，而不是始终将图像缩放到940x370。你可以这样做：

$scaleX = $width / $photoX;
$scaleY = $height / $photoY;
$scale = min($scaleX, $scaleY);

$scaleW = $scale * $photoX;
$scaleH = $scale * $photoY;

$images_fin = ImageCreateTrueColor($width, $height);

$background = ImageColorAllocate($images_fin, 0, 0, 0);
ImageFill($images_fin, 0, 0, $background);

ImageCopyResampled($images_fin, $images_orig, $width / 2 - $scaleW / 2, $height / 2 - $scaleH / 2, 0, 0, $scaleW+1, $scaleH+1, $photoX, $photoY);

这将确保生成的图像始终适合940x370尺寸。图像的其余部分（如果纵横比不与940匹配，则为370）将用黑色填充。

即使在使用PHP GD功能后，为什么在图像重新调整大小时上传图像质量的质量会受到严重影响？

1 个答案: