PHP如何生成自适应大小的缩略图

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。

2. define ( 'MAX_IMG_SIZE', 100000 );
3. // Supported image types
4. define ( 'THUMB_JPEG', 'image/jpeg' );
5. define ( 'THUMB_PNG', 'image/png' );
6. define ( 'THUMB_GIF', 'image/gif' );
7. // Interlacing modes
8. define ( 'INTERLACE_OFF', 0 );
9. define ( 'INTERLACE_ON', 1 );
10. // Output modes
11. define ( 'STDOUT', '' );
12. // Empty constants
13. define ( 'NO_LOGO', '' );
14. define ( 'NO_LABEL', '' );
15. // Logo and label positioning
16. define ( 'POS_LEFT', 0 );
17. define ( 'POS_RIGHT', 1 );
18. define ( 'POS_CENTER', 2 );
19. define ( 'POS_TOP', 3 );
20. define ( 'POS_BOTTOM', 4 );
21. // Error messages
22. define ( 'E_001', 'File %s do not exist' );
23. define ( 'E_002', 'Failed reading image data from %s' );
24. define ( 'E_003', 'Cannot create the copy of %s' );
25. define ( 'E_004', 'Cannot copy the logo image' );
26. define ( 'E_005', 'Cannot create final image' );
27. // ****************************************************************************
28. // CLASS DEFINITION
29. // ****************************************************************************
30. class ThumbnailImage
31. {
32. // ****************************************************************************
33. // PUBLIC PROPERTIES
34. // ****************************************************************************
35. var $src_file; // source image file
36. var $dest_file; // destination image file
37. var $dest_type; // destination image type
38. var $interlace; // destination image interlacing mode
39. var $jpeg_quality; // quality of resulting JPEG
40. var $max_width; // maximal thumbnail width
41. var $max_height; // maximal thumbnail height
42. var $fit_to_max; // enlarge small images?
43. var $logo; // array of logo parameters
44. var $label; // array of label parameters
45. // ****************************************************************************
46. // CLASS CONSTRUCTOR
47. // ****************************************************************************
48. /*
49. Description:
50. Defines default values for properties.
51. Prototype:
52. void ThumbImg ( string src_file = '' )
53. Parameters:
54. src_file - source image filename
55. */
56. function ThumbnailImage ( $src_file = '' )
57. {
58. $this->src_file = $src_file;
59. $this->dest_file = STDOUT;
60. $this->dest_type = THUMB_JPEG;
61. $this->interlace = INTERLACE_OFF;
62. $this->jpeg_quality = -1;
63. $this->max_width = 100;
64. $this->max_height = 90;
65. $this->fit_to_max = FALSE;
66. $this->logo['file'] = NO_LOGO;
67. $this->logo['vert_pos'] = POS_TOP;
68. $this->logo['horz_pos'] = POS_LEFT;
69. $this->label['text'] = NO_LABEL;
70. $this->label['vert_pos'] = POS_BOTTOM;
71. $this->label['horz_pos'] = POS_RIGHT;
72. $this->label['font'] = '';
73. $this->label['size'] = 20;
74. $this->label['color'] = '#000000';
75. $this->label['angle'] = 0;
76. }
77. // ****************************************************************************
78. // PRIVATE METHODS
79. // ****************************************************************************
80. /*
81. Description:
82. Extracts decimal color components from hex color string.
83. Prototype:
84. array ParseColor ( string hex_color )
85. Parameters:
86. hex_color - color in '#rrggbb' format
87. Return:
88. Decimal values for red, green and blue color components.
89. */
90. function ParseColor ( $hex_color )
91. {
92. if ( strpos ( $hex_color, '#' ) === 0 )
93. $hex_color = substr ( $hex_color, 1 );
94. $r = hexdec ( substr ( $hex_color, 0, 2 ) );
95. $g = hexdec ( substr ( $hex_color, 2, 2 ) );
96. $b = hexdec ( substr ( $hex_color, 4, 2 ) );
97. return array ( $r, $g, $b );
98. }
99. /*
100. Description:
101. Retrives image data as a string.
102. Thanks to Luis Larrateguy for the idea of this function.
103. Prototype:
104. string GetImageStr ( string image_file )
105. Parameters:
106. image_file - filename of image
107. Return:
108. Image file contents string.
109. */
110. function GetImageStr ( $image_file )
111. {
112. if ( function_exists ( 'file_get_contents' ) )
113. {
114. $str = @file_get_contents ( $image_file );
115. if ( ! $str )
116. {
117. $err = sprintf( E_002, $image_file );
118. trigger_error( $err, E_USER_ERROR );
119. }
120. return $str;
121. }
122. $f = fopen ( $image_file, 'rb' );
123. if ( ! $f )
124. {
125. $err = sprintf( E_002, $image_file );
126. trigger_error( $err, E_USER_ERROR );
127. }
128. $fsz = @filesize ( $image_file );
129. if ( ! $fsz )
130. $fsz = MAX_IMG_SIZE;
131. $str = fread ( $f, $fsz );
132. fclose ( $f );
133. return $str;
134. }
135. /*
136. Description:
137. Loads image from file.
138. Prototype:
139. resource LoadImage ( string image_file, int &image_width, int &image_height )
140. Parameters:
141. image_file - filename of image
142. image_width - width of loaded image
143. image_height - height of loaded image
144. Return:
145. Image identifier representing the image obtained from the given file.
146. */
147. function LoadImage ( $image_file, &$image_width, &$image_height )
148. {
149. $image_width = 0;
150. $image_height = 0;
151. $image_data = $this->GetImageStr( $image_file );
152. $image = imagecreatefromstring ( $image_data );
153. if ( ! $image )
154. {
155. $err = sprintf( E_003, $image_file );
156. trigger_error( $err, E_USER_ERROR );
157. }
158. $image_width = imagesx ( $image );
159. $image_height = imagesy ( $image );
160. return $image;
161. }
162. /*
163. Description:
164. Calculates thumbnail image sizes from source image width and height.
165. Prototype:
166. array GetThumbSize ( int src_width, int src_height )
167. Parameters:
168. src_width - width of source image
169. src_height - height of source image
170. Return:
171. An array with 2 elements. Index 0 contains the width of thumbnail image
172. and index 1 contains the height.
173. */ 生成缩略图
174. function GetThumbSize ( $src_width, $src_height )
175. {
176. $max_width = $this->max_width;
177. $max_height = $this->max_height;
178. $x_ratio = $max_width / $src_width;
179. $y_ratio = $max_height / $src_height;
180. $is_small = ( $src_width <= $max_width && $src_height <= $max_height );
181. if ( ! $this->fit_to_max && $is_small )
182. {
183. $dest_width = $src_width;
184. $dest_height = $src_height;
185. }
186. elseif ( $x_ratio * $src_height < $max_height )
187. {
188. $dest_width = $max_width;
189. $dest_height = ceil ( $x_ratio * $src_height );
190. }
191. else
192. {
193. $dest_width = ceil ( $y_ratio * $src_width );
194. $dest_height = $max_height;
195. }
196. return array ( $dest_width, $dest_height );
197. }
198. /*
199. Description:
200. Adds logo image to thumbnail.
201. Prototype:
202. void AddLogo ( int thumb_width, int thumb_height, resource &thumb_img )
203. Parameters:
204. thumb_width - width of thumbnail image
205. thumb_height - height of thumbnail image
206. thumb_img - thumbnail image identifier
207. */
208. function AddLogo ( $thumb_width, $thumb_height, &$thumb_img )
209. {
210. extract ( $this->logo );
211. $logo_image = $this->LoadImage ( $file, $logo_width, $logo_height );
212. if ( $vert_pos == POS_CENTER )
213. $y_pos = ceil ( $thumb_height / 2 - $logo_height / 2 );
214. elseif ($vert_pos == POS_BOTTOM)
215. $y_pos = $thumb_height - $logo_height;
216. else
217. $y_pos = 0;
218. if ( $horz_pos == POS_CENTER )
219. $x_pos = ceil ( $thumb_width / 2 - $logo_width / 2 );
220. elseif ( $horz_pos == POS_RIGHT )
221. $x_pos = $thumb_width - $logo_width;
222. else
223. $x_pos = 0;
224. if ( ! imagecopy ( $thumb_img, $logo_image, $x_pos, $y_pos, 0, 0,
225. $logo_width, $logo_height ) )
226. trigger_error( E_004, E_USER_ERROR );
227. }
228. /*
229. Description:
230. Adds label text to thumbnail.
231. Prototype:
232. void AddLabel ( int thumb_width, int thumb_height, resource &thumb_img )
233. Parameters:
234. thumb_width - width of thumbnail image
235. thumb_height - height of thumbnail image
236. thumb_img - thumbnail image identifier
237. */
238. function AddLabel ( $thumb_width, $thumb_height, &$thumb_img )
239. {
240. extract ( $this->label );
241. list( $r, $g, $b ) = $this->ParseColor ( $color );
242. $color_id = imagecolorallocate ( $thumb_img, $r, $g, $b );
243. $text_box = imagettfbbox ( $size, $angle, $font, $text );
244. $text_width = $text_box [ 2 ] - $text_box [ 0 ];
245. $text_height = abs ( $text_box [ 1 ] - $text_box [ 7 ] );
246. if ( $vert_pos == POS_TOP )
247. $y_pos = 5 + $text_height;
248. elseif ( $vert_pos == POS_CENTER )
249. $y_pos = ceil( $thumb_height / 2 - $text_height / 2 );
250. elseif ( $vert_pos == POS_BOTTOM )
251. $y_pos = $thumb_height - $text_height;
252. if ( $horz_pos == POS_LEFT )
253. $x_pos = 5;
254. elseif ( $horz_pos == POS_CENTER )
255. $x_pos = ceil( $thumb_width / 2 - $text_width / 2 );
256. elseif ( $horz_pos == POS_RIGHT )
257. $x_pos = $thumb_width - $text_width -5;
258. imagettftext ( $thumb_img, $size, $angle, $x_pos, $y_pos,
259. $color_id, $font, $text );
260. }
261. /*
262. Description:
263. Output thumbnail image into the browser.
264. Prototype:
265. void OutputThumbImage ( resource dest_image )
266. Parameters:
267. dest_img - thumbnail image identifier
268. */ 输出缩略图
269. function OutputThumbImage ( $dest_image )
270. {
271. imageinterlace ( $dest_image, $this->interlace );
272. header ( 'Content-type: ' . $this->dest_type );
273. if ( $this->dest_type == THUMB_JPEG )
274. imagejpeg ( $dest_image, '', $this->jpeg_quality );
275. elseif ( $this->dest_type == THUMB_GIF )
276. imagegif($dest_image);
277. elseif ( $this->dest_type == THUMB_PNG )
278. imagepng ( $dest_image );
279. }
280. /*
281. Description:
282. Save thumbnail image into the disc file.
283. Prototype:
284. void SaveThumbImage ( string image_file, resource dest_image )
285. Parameters:
286. image_file - destination file name
287. dest_img - thumbnail image identifier
288. */
289. function SaveThumbImage ( $image_file, $dest_image )
290. {
291. imageinterlace ( $dest_image, $this->interlace );
292. if ( $this->dest_type == THUMB_JPEG )
293. imagejpeg ( $dest_image, $this->dest_file, $this->jpeg_quality );
294. elseif ( $this->dest_type == THUMB_GIF )
295. imagegif ( $dest_image, $this->dest_file );
296. elseif ( $this->dest_type == THUMB_PNG )
297. imagepng ( $dest_image, $this->dest_file );
298. }
299. // ****************************************************************************
300. // PUBLIC METHODS
301. // ****************************************************************************
302. /*
303. Description:
304. Output thumbnail image into the browser or disc file according to the
305. values of parameters.
306. Prototype:
307. void Output ( )
308. */ 生成缩略图片
309. function Output()
310. {
311. $src_image = $this->LoadImage($this->src_file, $src_width, $src_height);
312. $dest_size = $this->GetThumbSize($src_width, $src_height);
313. $dest_width=$dest_size[0];
314. $dest_height=$dest_size[1];
315. $dest_image=imagecreatetruecolor($dest_width, $dest_height);
316. if (!$dest_image)
317. trigger_error(E_005, E_USER_ERROR);
318. imagecopyresampled( $dest_image, $src_image, 0, 0, 0, 0,
319. $dest_width, $dest_height, $src_width, $src_height );
320. if ($this->logo['file'] != NO_LOGO)
321. $this->AddLogo($dest_width, $dest_height, $dest_image);
322. if ($this->label['text'] != NO_LABEL)
323. $this->AddLabel($dest_width, $dest_height, $dest_image);
324. if ($this->dest_file == STDOUT)
325. $this->OutputThumbImage ( $dest_image );
326. else
327. $this->SaveThumbImage ( $this->dest_file, $dest_image );
328. imagedestroy ( $src_image );
329. imagedestroy ( $dest_image );
330. }
331. } // End of class definition
332. ?>

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

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

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。