PHP如何生成自适应大小的缩略图 -tutorial php-php.cn

生成缩略图的php类，新建一个文件叫做 thumbnailimage.php，文件名最好不要用大写。

define ( 'MAX_IMG_SIZE', 100000 );
// Supported image types
define ( 'THUMB_JPEG', 'image/jpeg' );
define ( 'THUMB_PNG', 'image/png' );
define ( 'THUMB_GIF', 'image/gif' );
// Interlacing modes
define ( 'INTERLACE_OFF', 0 );
define ( 'INTERLACE_ON', 1 );
// Output modes
define ( 'STDOUT', '' );
// Empty constants
define ( 'NO_LOGO', '' );
define ( 'NO_LABEL', '' );
// Logo and label positioning
define ( 'POS_LEFT', 0 );
define ( 'POS_RIGHT', 1 );
define ( 'POS_CENTER', 2 );
define ( 'POS_TOP', 3 );
define ( 'POS_BOTTOM', 4 );
// Error messages
define ( 'E_001', 'File %s do not exist' );
define ( 'E_002', 'Failed reading image data from %s' );
define ( 'E_003', 'Cannot create the copy of %s' );
define ( 'E_004', 'Cannot copy the logo image' );
define ( 'E_005', 'Cannot create final image' );
// ****************************************************************************
// CLASS DEFINITION
// ****************************************************************************
class ThumbnailImage
{
// ****************************************************************************
// PUBLIC PROPERTIES
// ****************************************************************************
var $src_file; // source image file
var $dest_file; // destination image file
var $dest_type; // destination image type
var $interlace; // destination image interlacing mode
var $jpeg_quality; // quality of resulting JPEG
var $max_width; // maximal thumbnail width
var $max_height; // maximal thumbnail height
var $fit_to_max; // enlarge small images?
var $logo; // array of logo parameters
var $label; // array of label parameters
// ****************************************************************************
// CLASS CONSTRUCTOR
// ****************************************************************************
/*
Description:
Defines default values for properties.
Prototype:
void ThumbImg ( string src_file = '' )
Parameters:
src_file - source image filename
*/
function ThumbnailImage ( $src_file = '' )
{
$this->src_file = $src_file;
$this->dest_file = STDOUT;
$this->dest_type = THUMB_JPEG;
$this->interlace = INTERLACE_OFF;
$this->jpeg_quality = -1;
$this->max_width = 100;
$this->max_height = 90;
$this->fit_to_max = FALSE;
$this->logo['file'] = NO_LOGO;
$this->logo['vert_pos'] = POS_TOP;
$this->logo['horz_pos'] = POS_LEFT;
$this->label['text'] = NO_LABEL;
$this->label['vert_pos'] = POS_BOTTOM;
$this->label['horz_pos'] = POS_RIGHT;
$this->label['font'] = '';
$this->label['size'] = 20;
$this->label['color'] = '#000000';
$this->label['angle'] = 0;
}
// ****************************************************************************
// PRIVATE METHODS
// ****************************************************************************
/*
Description:
Extracts decimal color components from hex color string.
Prototype:
array ParseColor ( string hex_color )
Parameters:
hex_color - color in '#rrggbb' format
Return:
Decimal values for red, green and blue color components.
*/
function ParseColor ( $hex_color )
{
if ( strpos ( $hex_color, '#' ) === 0 )
$hex_color = substr ( $hex_color, 1 );
$r = hexdec ( substr ( $hex_color, 0, 2 ) );
$g = hexdec ( substr ( $hex_color, 2, 2 ) );
$b = hexdec ( substr ( $hex_color, 4, 2 ) );
return array ( $r, $g, $b );
}
/*
Description:
Retrives image data as a string.
Thanks to Luis Larrateguy for the idea of this function.
Prototype:
string GetImageStr ( string image_file )
Parameters:
image_file - filename of image
Return:
Image file contents string.
*/
function GetImageStr ( $image_file )
{
if ( function_exists ( 'file_get_contents' ) )
{
$str = @file_get_contents ( $image_file );
if ( ! $str )
{
$err = sprintf( E_002, $image_file );
trigger_error( $err, E_USER_ERROR );
}
return $str;
}
$f = fopen ( $image_file, 'rb' );
if ( ! $f )
{
$err = sprintf( E_002, $image_file );
trigger_error( $err, E_USER_ERROR );
}
$fsz = @filesize ( $image_file );
if ( ! $fsz )
$fsz = MAX_IMG_SIZE;
$str = fread ( $f, $fsz );
fclose ( $f );
return $str;
}
/*
Description:
Loads image from file.
Prototype:
resource LoadImage ( string image_file, int &image_width, int &image_height )
Parameters:
image_file - filename of image
image_width - width of loaded image
image_height - height of loaded image
Return:
Image identifier representing the image obtained from the given file.
*/
function LoadImage ( $image_file, &$image_width, &$image_height )
{
$image_width = 0;
$image_height = 0;
$image_data = $this->GetImageStr( $image_file );
$image = imagecreatefromstring ( $image_data );
if ( ! $image )
{
$err = sprintf( E_003, $image_file );
trigger_error( $err, E_USER_ERROR );
}
$image_width = imagesx ( $image );
$image_height = imagesy ( $image );
return $image;
}
/*
Description:
Calculates thumbnail image sizes from source image width and height.
Prototype:
array GetThumbSize ( int src_width, int src_height )
Parameters:
src_width - width of source image
src_height - height of source image
Return:
An array with 2 elements. Index 0 contains the width of thumbnail image
and index 1 contains the height.
*/ 生成缩略图
function GetThumbSize ( $src_width, $src_height )
{
$max_width = $this->max_width;
$max_height = $this->max_height;
$x_ratio = $max_width / $src_width;
$y_ratio = $max_height / $src_height;
$is_small = ( $src_width if ( ! $this->fit_to_max && $is_small )
{
$dest_width = $src_width;
$dest_height = $src_height;
}
elseif ( $x_ratio * $src_height {
$dest_width = $max_width;
$dest_height = ceil ( $x_ratio * $src_height );
}
else
{
$dest_width = ceil ( $y_ratio * $src_width );
$dest_height = $max_height;
}
return array ( $dest_width, $dest_height );
}
/*
Description:
Adds logo image to thumbnail.
Prototype:
void AddLogo ( int thumb_width, int thumb_height, resource &thumb_img )
Parameters:
thumb_width - width of thumbnail image
thumb_height - height of thumbnail image
thumb_img - thumbnail image identifier
*/
function AddLogo ( $thumb_width, $thumb_height, &$thumb_img )
{
extract ( $this->logo );
$logo_image = $this->LoadImage ( $file, $logo_width, $logo_height );
if ( $vert_pos == POS_CENTER )
$y_pos = ceil ( $thumb_height / 2 - $logo_height / 2 );
elseif ($vert_pos == POS_BOTTOM)
$y_pos = $thumb_height - $logo_height;
else
$y_pos = 0;
if ( $horz_pos == POS_CENTER )
$x_pos = ceil ( $thumb_width / 2 - $logo_width / 2 );
elseif ( $horz_pos == POS_RIGHT )
$x_pos = $thumb_width - $logo_width;
else
$x_pos = 0;
if ( ! imagecopy ( $thumb_img, $logo_image, $x_pos, $y_pos, 0, 0,
$logo_width, $logo_height ) )
trigger_error( E_004, E_USER_ERROR );
}
/*
Description:
Adds label text to thumbnail.
Prototype:
void AddLabel ( int thumb_width, int thumb_height, resource &thumb_img )
Parameters:
thumb_width - width of thumbnail image
thumb_height - height of thumbnail image
thumb_img - thumbnail image identifier
*/
function AddLabel ( $thumb_width, $thumb_height, &$thumb_img )
{
extract ( $this->label );
list( $r, $g, $b ) = $this->ParseColor ( $color );
$color_id = imagecolorallocate ( $thumb_img, $r, $g, $b );
$text_box = imagettfbbox ( $size, $angle, $font, $text );
$text_width = $text_box [ 2 ] - $text_box [ 0 ];
$text_height = abs ( $text_box [ 1 ] - $text_box [ 7 ] );
if ( $vert_pos == POS_TOP )
$y_pos = 5 + $text_height;
elseif ( $vert_pos == POS_CENTER )
$y_pos = ceil( $thumb_height / 2 - $text_height / 2 );
elseif ( $vert_pos == POS_BOTTOM )
$y_pos = $thumb_height - $text_height;
if ( $horz_pos == POS_LEFT )
$x_pos = 5;
elseif ( $horz_pos == POS_CENTER )
$x_pos = ceil( $thumb_width / 2 - $text_width / 2 );
elseif ( $horz_pos == POS_RIGHT )
$x_pos = $thumb_width - $text_width -5;
imagettftext ( $thumb_img, $size, $angle, $x_pos, $y_pos,
$color_id, $font, $text );
}
/*
Description:
Output thumbnail image into the browser.
Prototype:
void OutputThumbImage ( resource dest_image )
Parameters:
dest_img - thumbnail image identifier
*/ 输出缩略图
function OutputThumbImage ( $dest_image )
{
imageinterlace ( $dest_image, $this->interlace );
header ( 'Content-type: ' . $this->dest_type );
if ( $this->dest_type == THUMB_JPEG )
imagejpeg ( $dest_image, '', $this->jpeg_quality );
elseif ( $this->dest_type == THUMB_GIF )
imagegif($dest_image);
elseif ( $this->dest_type == THUMB_PNG )
imagepng ( $dest_image );
}
/*
Description:
Save thumbnail image into the disc file.
Prototype:
void SaveThumbImage ( string image_file, resource dest_image )
Parameters:
image_file - destination file name
dest_img - thumbnail image identifier
*/
function SaveThumbImage ( $image_file, $dest_image )
{
imageinterlace ( $dest_image, $this->interlace );
if ( $this->dest_type == THUMB_JPEG )
imagejpeg ( $dest_image, $this->dest_file, $this->jpeg_quality );
elseif ( $this->dest_type == THUMB_GIF )
imagegif ( $dest_image, $this->dest_file );
elseif ( $this->dest_type == THUMB_PNG )
imagepng ( $dest_image, $this->dest_file );
}
// ****************************************************************************
// PUBLIC METHODS
// ****************************************************************************
/*
Description:
Output thumbnail image into the browser or disc file according to the
values of parameters.
Prototype:
void Output ( )
*/ 生成缩略图片
function Output()
{
$src_image = $this->LoadImage($this->src_file, $src_width, $src_height);
$dest_size = $this->GetThumbSize($src_width, $src_height);
$dest_width=$dest_size[0];
$dest_height=$dest_size[1];
$dest_image=imagecreatetruecolor($dest_width, $dest_height);
if (!$dest_image)
trigger_error(E_005, E_USER_ERROR);
imagecopyresampled( $dest_image, $src_image, 0, 0, 0, 0,
$dest_width, $dest_height, $src_width, $src_height );
if ($this->logo['file'] != NO_LOGO)
$this->AddLogo($dest_width, $dest_height, $dest_image);
if ($this->label['text'] != NO_LABEL)
$this->AddLabel($dest_width, $dest_height, $dest_image);
if ($this->dest_file == STDOUT)
$this->OutputThumbImage ( $dest_image );
else
$this->SaveThumbImage ( $this->dest_file, $dest_image );
imagedestroy ( $src_image );
imagedestroy ( $dest_image );
}
} // End of class definition
?>

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使用方法： 1、首先引用该php文件（不要告诉我不会) 2、调用代码

$tis = new ThumbnailImage();
$tis->src_file = "这里写源文件的路径"
$tis->dest_type = THUMB_JPEG;//生成图片的类型是 jpg
$tis->dest_file = '这里写目标文件的路径';
$tis->max_width = 120;//自适应大小，但是最大宽度为120
$tis->max_height = 4000; //自适应大小，但是最大高度为4000
$tis->Output();

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代码关键在于： max_width 和max_height，一般来说除非图片很有个性，否则缩略图生成的还是很不错的。