本文实例讲述了php使用GD创建保持宽高比缩略图的方法。分享给大家供大家参考。具体如下：

/** * Create a thumbnail image from $inputFileName no taller or wider than * $maxSize. Returns the new image resource or false on error. * Author: mthorn.net */ function thumbnail($inputFileName, $maxSize = 100) { $info = getimagesize($inputFileName); $type = isset($info['type']) ? $info['type'] : $info[2]; // Check support of file type if ( !(imagetypes() & $type) ) { // Server does not support file type return false; } $width = isset($info['width']) ? $info['width'] : $info[0]; $height = isset($info['height']) ? $info['height'] : $info[1]; // Calculate aspect ratio $wRatio = $maxSize / $width; $hRatio = $maxSize / $height; // Using imagecreatefromstring will automatically detect the file type $sourceImage = imagecreatefromstring(file_get_contents($inputFileName)); // Calculate a proportional width and height no larger than the max size. if ( ($width <= $maxSize) && ($height <= $maxSize) ) { // Input is smaller than thumbnail, do nothing return $sourceImage; } elseif ( ($wRatio * $height) < $maxSize ) { // Image is horizontal $tHeight = ceil($wRatio * $height); $tWidth = $maxSize; } else { // Image is vertical $tWidth = ceil($hRatio * $width); $tHeight = $maxSize; } $thumb = imagecreatetruecolor($tWidth, $tHeight); if ( $sourceImage === false ) { // Could not load image return false; } // Copy resampled makes a smooth thumbnail imagecopyresampled($thumb,$sourceImage,0,0,0,0,$tWidth,$tHeight,$width,$height); imagedestroy($sourceImage); return $thumb; } /** * Save the image to a file. Type is determined from the extension. * $quality is only used for jpegs. * Author: mthorn.net */ function imageToFile($im, $fileName, $quality = 80) { if ( !$im || file_exists($fileName) ) { return false; } $ext = strtolower(substr($fileName, strrpos($fileName, '.'))); switch ( $ext ) { case '.gif': imagegif($im, $fileName); break; case '.jpg': case '.jpeg': imagejpeg($im, $fileName, $quality); break; case '.png': imagepng($im, $fileName); break; case '.bmp': imagewbmp($im, $fileName); break; default: return false; } return true; } $im = thumbnail('temp.jpg', 100); imageToFile($im, 'temp-thumbnail.jpg');

希望本文所述对大家的php程序设计有所帮助。