仿GD读取bmp函数

最近在工作中需要把bmp图片转成jpg图片，但无奈的是网上能找到的bmp转gd的类或函数或多或少都有些问题。其中绝大多数在处理16位bmp图片时要么全黑全粉，要么干脆转换不出，其余有些根本不支持32位的bmp图片。
最后我终于在php的官网上找到了解决方法。原来网上流传最广的一个仿GD的imagecreatefrombmp函数是一个有问题的版本，无法正确处理16位bmp图片，但好在官网上有人给出了修正方法，修正好的代码如下：

1. /**
2. * BMP 创建函数
3. * @author simon
4. * @modified by 天心流水
5. * @param string $filename path of bmp file
6. * @example who use,who knows
7. * @return resource of GD
8. */
9. function imagecreatefrombmp( $filename ) {
10. if ( !$f1 = fopen( $filename, "rb" ) )
11. return FALSE;
13. $FILE = unpack( "vfile_type/Vfile_size/Vreserved/Vbitmap_offset", fread( $f1, 14 ) );
14. if ( $FILE['file_type'] != 19778 )
15. return FALSE;
17. $BMP = unpack( 'Vheader_size/Vwidth/Vheight/vplanes/vbits_per_pixel' . '/Vcompression/Vsize_bitmap/Vhoriz_resolution' . '/Vvert_resolution/Vcolors_used/Vcolors_important', fread( $f1, 40 ) );
18. $BMP['colors'] = pow( 2, $BMP['bits_per_pixel'] );
19. if ( $BMP['size_bitmap'] == 0 )
20. $BMP['size_bitmap'] = $FILE['file_size'] - $FILE['bitmap_offset'];
21. $BMP['bytes_per_pixel'] = $BMP['bits_per_pixel'] / 8;
22. $BMP['bytes_per_pixel2'] = ceil( $BMP['bytes_per_pixel'] );
23. $BMP['decal'] = ($BMP['width'] * $BMP['bytes_per_pixel'] / 4);
24. $BMP['decal'] -= floor( $BMP['width'] * $BMP['bytes_per_pixel'] / 4 );
25. $BMP['decal'] = 4 - (4 * $BMP['decal']);
26. if ( $BMP['decal'] == 4 )
27. $BMP['decal'] = 0;
29. $PALETTE = array();
30. if ($BMP['colors'] {
31. $PALETTE = unpack('V'.$BMP['colors'], fread($f1,$BMP['colors']*4));
32. }
34. $IMG = fread( $f1, $BMP['size_bitmap'] );
35. $VIDE = chr( 0 );
37. $res = imagecreatetruecolor( $BMP['width'], $BMP['height'] );
38. $P = 0;
39. $Y = $BMP['height'] - 1;
40. while( $Y >= 0 ){
41. $X = 0;
42. while( $X if ( $BMP['bits_per_pixel'] == 32 ){
43. $COLOR = unpack( "V", substr( $IMG, $P, 3 ) );
44. $B = ord(substr($IMG, $P,1));
45. $G = ord(substr($IMG, $P+1,1));
46. $R = ord(substr($IMG, $P+2,1));
47. $color = imagecolorexact( $res, $R, $G, $B );
48. if ( $color == -1 )
49. $color = imagecolorallocate( $res, $R, $G, $B );
50. $COLOR[0] = $R*256*256+$G*256+$B;
51. $COLOR[1] = $color;
52. } elseif ( $BMP['bits_per_pixel'] == 24 ) {
53. $COLOR = unpack( "V", substr( $IMG, $P, 3 ) . $VIDE );
54. } elseif ( $BMP['bits_per_pixel'] == 16 ){
55. $COLOR = unpack("v",substr($IMG,$P,2));
56. $blue = (($COLOR[1] & 0x001f) $green = (($COLOR[1] & 0x03e0) >> 2) + 7;
57. $red = (($COLOR[1] & 0xfc00) >> 7) + 7;
58. $COLOR[1] = $red * 65536 + $green * 256 + $blue;
59. } elseif ( $BMP['bits_per_pixel'] == 8 ){
60. $COLOR = unpack( "n", $VIDE . substr( $IMG, $P, 1 ) );
61. $COLOR[1] = $PALETTE[$COLOR[1] + 1];
62. } elseif ( $BMP['bits_per_pixel'] == 4 ){
63. $COLOR = unpack( "n", $VIDE . substr( $IMG, floor( $P ), 1 ) );
64. if ( ($P * 2) % 2 == 0 )
65. $COLOR[1] = ($COLOR[1] >> 4);
66. else
67. $COLOR[1] = ($COLOR[1] & 0x0F);
68. $COLOR[1] = $PALETTE[$COLOR[1] + 1];
69. } elseif ( $BMP['bits_per_pixel'] == 1 ){
70. $COLOR = unpack( "n", $VIDE . substr( $IMG, floor( $P ), 1 ) );
71. if ( ($P * 8) % 8 == 0 )
72. $COLOR[1] = $COLOR[1] >> 7;
73. elseif ( ($P * 8) % 8 == 1 )
74. $COLOR[1] = ($COLOR[1] & 0x40) >> 6;
75. elseif ( ($P * 8) % 8 == 2 )
76. $COLOR[1] = ($COLOR[1] & 0x20) >> 5;
77. elseif ( ($P * 8) % 8 == 3 )
78. $COLOR[1] = ($COLOR[1] & 0x10) >> 4;
79. elseif ( ($P * 8) % 8 == 4 )
80. $COLOR[1] = ($COLOR[1] & 0x8) >> 3;
81. elseif ( ($P * 8) % 8 == 5 )
82. $COLOR[1] = ($COLOR[1] & 0x4) >> 2;
83. elseif ( ($P * 8) % 8 == 6 )
84. $COLOR[1] = ($COLOR[1] & 0x2) >> 1;
85. elseif ( ($P * 8) % 8 == 7 )
86. $COLOR[1] = ($COLOR[1] & 0x1);
87. $COLOR[1] = $PALETTE[$COLOR[1] + 1];
88. }else
89. return FALSE;
90. imagesetpixel( $res, $X, $Y, $COLOR[1] );
91. $X++;
92. $P += $BMP['bytes_per_pixel'];
93. }
94. $Y--;
95. $P += $BMP['decal'];
96. }
97. fclose( $f1 );
99. return $res;
100. }

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