1. /*--------------------------------------------------------------------------
2. Process one of the nested EXIF directories.
3. --------------------------------------------------------------------------*/
4. bool Cexif::ProcessExifDir(unsigned char * DirStart, unsigned char * OffsetBase, unsigned ExifLength,
5. EXIFINFO * const m_exifinfo, unsigned char ** const LastExifRefdP )
6. {
7. int de;
8. int a;
9. int NumDirEntries;
10. unsigned ThumbnailOffset = 0;
11. unsigned ThumbnailSize = 0;
12. unsigned long gps = 0;
13. NumDirEntries = Get16u(DirStart);
14. if ((DirStart+2+NumDirEntries*12) > (OffsetBase+ExifLength)){
15. strcpy(m_szLastError,"Illegally sized directory");
16. return 0;
17. }
18. for (de=0;de<NumDirEntries;de++)
19. {
20. int Tag, Format, Components;
21. unsigned char * ValuePtr;
22. /* This actually can point to a variety of things; it must be
23. cast to other types when used. But we use it as a unsigned char-by-unsigned char
24. cursor, so we declare it as a pointer to a generic unsigned char here.
25. */
26. int BytesCount;
27. unsigned char * DirEntry;
28. DirEntry = DirStart+2+12*de;
29. Tag = Get16u(DirEntry);
30. Format = Get16u(DirEntry+2);
31. Components = Get32u(DirEntry+4);
32. if ((Format-1) >= NUM_FORMATS) {
33. /* (-1) catches illegal zero case as unsigned underflows to positive large */
34. strcpy(m_szLastError,"Illegal format code in EXIF dir");
35. return 0;
36. }
37. BytesCount = Components * BytesPerFormat[Format];
38. if (BytesCount > 4){
39. unsigned OffsetVal;
40. OffsetVal = Get32u(DirEntry+8);
41. /* If its bigger than 4 unsigned chars, the dir entry contains an offset.*/
42. if (OffsetVal+BytesCount > ExifLength){
43. /* Bogus pointer offset and / or unsigned charcount value */
44. strcpy(m_szLastError,"Illegal pointer offset value in EXIF.");
45. return 0;
46. }
47. ValuePtr = OffsetBase+OffsetVal;
48. }else{
49. /* 4 unsigned chars or less and value is in the dir entry itself */
50. ValuePtr = DirEntry+8;
51. }
52. if (*LastExifRefdP < ValuePtr+BytesCount){
53. /* Keep track of last unsigned char in the exif header that was
54. actually referenced. That way, we know where the
55. discardable thumbnail data begins.
56. */
57. *LastExifRefdP = ValuePtr+BytesCount;
58. }
59. /* Extract useful components of tag */
60. switch(Tag){
61. case TAG_MAKE:
62. strncpy(m_exifinfo->CameraMake, (char*)ValuePtr, 31);
63. break;
64. case TAG_MODEL:
65. strncpy(m_exifinfo->CameraModel, (char*)ValuePtr, 39);
66. break;
67. case TAG_EXIF_VERSION:
68. strncpy(m_exifinfo->Version,(char*)ValuePtr, 4);
69. break;
70. case TAG_DATETIME_ORIGINAL:
71. strncpy(m_exifinfo->DateTime, (char*)ValuePtr, 19);
72. break;
73. case TAG_USERCOMMENT:
74. // Olympus has this padded with trailing spaces. Remove these first.
75. for (a=BytesCount;;){
76. a--;
77. if (((char*)ValuePtr)[a] == ' '){
78. ((char*)ValuePtr)[a] = '\0';
79. }else{
80. break;
81. }
82. if (a == 0) break;
83. }
84. /* Copy the comment */
85. if (memcmp(ValuePtr, "ASCII",5) == 0){
86. for (a=5;a<10;a++){
87. char c;
88. c = ((char*)ValuePtr)[a];
89. if (c != '\0' && c != ' '){
90. strncpy(m_exifinfo->Comments, (char*)ValuePtr+a, 199);
91. break;
92. }
93. }
94. }else{
95. strncpy(m_exifinfo->Comments, (char*)ValuePtr, 199);
96. }
97. break;
98. case TAG_FNUMBER:
99. /* Simplest way of expressing aperture, so I trust it the most.
100. (overwrite previously computd value if there is one)
101. */
102. m_exifinfo->ApertureFNumber = (float)ConvertAnyFormat(ValuePtr, Format);
103. break;
104. case TAG_APERTURE:
105. case TAG_MAXAPERTURE:
106. /* More relevant info always comes earlier, so only
107. use this field if we don't have appropriate aperture
108. information yet.
109. */
110. if (m_exifinfo->ApertureFNumber == 0){
111. m_exifinfo->ApertureFNumber = (float)exp(ConvertAnyFormat(ValuePtr, Format)*log(2.0)*0.5);
112. }
113. break;
114. case TAG_BRIGHTNESS:
115. m_exifinfo->Brightness = (float)ConvertAnyFormat(ValuePtr, Format);
116. break;
117. case TAG_FOCALLENGTH:
118. /* Nice digital cameras actually save the focal length
119. as a function of how farthey are zoomed in.
120. */
121. m_exifinfo->FocalLength = (float)ConvertAnyFormat(ValuePtr, Format);
122. break;
123. case TAG_SUBJECT_DISTANCE:
124. /* Inidcates the distacne the autofocus camera is focused to.
125. Tends to be less accurate as distance increases.
126. */
127. m_exifinfo->Distance = (float)ConvertAnyFormat(ValuePtr, Format);
128. break;
129. case TAG_EXPOSURETIME:
130. /* Simplest way of expressing exposure time, so I
131. trust it most. (overwrite previously computd value
132. if there is one)
133. */
134. m_exifinfo->ExposureTime =
135. (float)ConvertAnyFormat(ValuePtr, Format);
136. break;
137. case TAG_SHUTTERSPEED:
138. /* More complicated way of expressing exposure time,
139. so only use this value if we don't already have it
140. from somewhere else.
141. */
142. if (m_exifinfo->ExposureTime == 0){
143. m_exifinfo->ExposureTime = (float)
144. (1/exp(ConvertAnyFormat(ValuePtr, Format)*log(2.0)));
145. }
146. break;
147. case TAG_FLASH:
148. if ((int)ConvertAnyFormat(ValuePtr, Format) & 7){
149. m_exifinfo->FlashUsed = 1;
150. }else{
151. m_exifinfo->FlashUsed = 0;
152. }
153. break;
154. case TAG_ORIENTATION:
155. m_exifinfo->Orientation = (int)ConvertAnyFormat(ValuePtr, Format);
156. if (m_exifinfo->Orientation < 1 || m_exifinfo->Orientation > 8){
157. strcpy(m_szLastError,"Undefined rotation value");
158. m_exifinfo->Orientation = 0;
159. }
160. break;
161. case TAG_EXIF_IMAGELENGTH:
162. case TAG_EXIF_IMAGEWIDTH:
163. /* Use largest of height and width to deal with images
164. that have been rotated to portrait format.
165. */
166. a = (int)ConvertAnyFormat(ValuePtr, Format);
167. if (ExifImageWidth < a) ExifImageWidth = a;
168. break;
169. case TAG_FOCALPLANEXRES:
170. m_exifinfo->FocalplaneXRes = (float)ConvertAnyFormat(ValuePtr, Format);
171. break;
172. case TAG_FOCALPLANEYRES:
173. m_exifinfo->FocalplaneYRes = (float)ConvertAnyFormat(ValuePtr, Format);
174. break;
175. case TAG_RESOLUTIONUNIT:
176. switch((int)ConvertAnyFormat(ValuePtr, Format)){
177. case 1: m_exifinfo->ResolutionUnit = 1.0f; break; /* 1 inch */
178. case 2: m_exifinfo->ResolutionUnit = 1.0f; break;
179. case 3: m_exifinfo->ResolutionUnit = 0.3937007874f; break; /* 1 centimeter*/
180. case 4: m_exifinfo->ResolutionUnit = 0.03937007874f; break; /* 1 millimeter*/
181. case 5: m_exifinfo->ResolutionUnit = 0.00003937007874f; /* 1 micrometer*/
182. }
183. break;
184. case TAG_FOCALPLANEUNITS:
185. switch((int)ConvertAnyFormat(ValuePtr, Format)){
186. case 1: m_exifinfo->FocalplaneUnits = 1.0f; break; /* 1 inch */
187. case 2: m_exifinfo->FocalplaneUnits = 1.0f; break;
188. case 3: m_exifinfo->FocalplaneUnits = 0.3937007874f; break; /* 1 centimeter*/
189. case 4: m_exifinfo->FocalplaneUnits = 0.03937007874f; break; /* 1 millimeter*/
190. case 5: m_exifinfo->FocalplaneUnits = 0.00003937007874f; /* 1 micrometer*/
191. }
192. break;
193. // Remaining cases contributed by: Volker C. Schoech <schoech(at)gmx(dot)de>
194. case TAG_EXPOSURE_BIAS:
195. m_exifinfo->ExposureBias = (float) ConvertAnyFormat(ValuePtr, Format);
196. break;
197. case TAG_WHITEBALANCE:
198. m_exifinfo->Whitebalance = (int)ConvertAnyFormat(ValuePtr, Format);
199. break;
200. case TAG_METERING_MODE:
201. m_exifinfo->MeteringMode = (int)ConvertAnyFormat(ValuePtr, Format);
202. break;
203. case TAG_EXPOSURE_PROGRAM:
204. m_exifinfo->ExposureProgram = (int)ConvertAnyFormat(ValuePtr, Format);
205. break;
206. case TAG_ISO_EQUIVALENT:
207. m_exifinfo->ISOequivalent = (int)ConvertAnyFormat(ValuePtr, Format);
208. if ( m_exifinfo->ISOequivalent < 50 ) m_exifinfo->ISOequivalent *= 200;
209. break;
210. case TAG_COMPRESSION_LEVEL:
211. m_exifinfo->CompressionLevel = (int)ConvertAnyFormat(ValuePtr, Format);
212. break;
213. case TAG_XRESOLUTION:
214. m_exifinfo->Xresolution = (float)ConvertAnyFormat(ValuePtr, Format);
215. break;
216. case TAG_YRESOLUTION:
217. m_exifinfo->Yresolution = (float)ConvertAnyFormat(ValuePtr, Format);
218. break;
219. case TAG_THUMBNAIL_OFFSET:
220. ThumbnailOffset = (unsigned)ConvertAnyFormat(ValuePtr, Format);
221. break;
222. case TAG_THUMBNAIL_LENGTH:
223. ThumbnailSize = (unsigned)ConvertAnyFormat(ValuePtr, Format);
224. break;
225. case TAG_GPS_INFO:
226. unsigned char * SubdirStart;
227. SubdirStart = OffsetBase + Get32u(ValuePtr);
228. CalGPS(SubdirStart, OffsetBase);
229. break;
230. }
231. if (Tag == TAG_EXIF_OFFSET || Tag == TAG_INTEROP_OFFSET || Tag == TAG_GPS_INFO)
232. {
233. unsigned char * SubdirStart;
234. SubdirStart = OffsetBase + Get32u(ValuePtr);
235. if (SubdirStart < OffsetBase ||
236. SubdirStart > OffsetBase+ExifLength){
237. strcpy(m_szLastError,"Illegal subdirectory link");
238. return 0;
239. }
240. ProcessExifDir(SubdirStart, OffsetBase, ExifLength, m_exifinfo, LastExifRefdP);
241. continue;
242. }
243. }
244. {
245. /* In addition to linking to subdirectories via exif tags,
246. there's also a potential link to another directory at the end
247. of each directory. This has got to be the result of a
248. committee!
249. */
250. unsigned char * SubdirStart;
251. unsigned Offset;
252. Offset = Get16u(DirStart+2+12*NumDirEntries);
253. if (Offset){
254. SubdirStart = OffsetBase + Offset;
255. if (SubdirStart < OffsetBase
256. || SubdirStart > OffsetBase+ExifLength){
257. strcpy(m_szLastError,"Illegal subdirectory link");
258. return 0;
259. }
260. ProcessExifDir(SubdirStart, OffsetBase, ExifLength, m_exifinfo, LastExifRefdP);
261. }
262. }
263. if (ThumbnailSize && ThumbnailOffset){
264. if (ThumbnailSize + ThumbnailOffset <= ExifLength){
265. /* The thumbnail pointer appears to be valid. Store it. */
266. m_exifinfo->ThumbnailPointer = OffsetBase + ThumbnailOffset;
267. m_exifinfo->ThumbnailSize = ThumbnailSize;
268. }
269. }
270. return 1;
271. }

Demo最终实现的结果