1 /*
2 * write-exif.c
3 *
4 * Create a new EXIF data block and write it into a JPEG image file.
5 *
6 * The JPEG image data used in this example is fixed and is guaranteed not
7 * to contain an EXIF tag block already, so it is easy to precompute where
8 * in the file the EXIF data should be. In real life, a library like
9 * libjpeg (included with the exif command-line tool source code) would
10 * be used to write to an existing JPEG file.
11 *
12 * SPDX-FileCopyrightText: Placed into the public domain by Dan Fandrich
13 * SPDX-License-Identifier: CC0-1.0
14 */
15
16 #include <stdio.h>
17 #include <stdlib.h>
18 #include <string.h>
19 #include <assert.h>
20 #include <libexif/exif-data.h>
21
22 /* this file will be unilaterally overwritten */
23 #define FILE_NAME "write-exif.jpg"
24
25 /* raw JPEG image data */
26 static const unsigned char image_jpg[] = {
27 0xff, 0xd8, 0xff, 0xe0, 0x00, 0x10, 0x4a, 0x46, 0x49, 0x46, 0x00, 0x01,
28 0x01, 0x01, 0x00, 0x48, 0x00, 0x48, 0x00, 0x00, 0xff, 0xdb, 0x00, 0x43,
29 0x00, 0x14, 0x0e, 0x0f, 0x12, 0x0f, 0x0d, 0x14, 0x12, 0x10, 0x12, 0x17,
30 0x15, 0x14, 0x18, 0x1e, 0x32, 0x21, 0x1e, 0x1c, 0x1c, 0x1e, 0x3d, 0x2c,
31 0x2e, 0x24, 0x32, 0x49, 0x40, 0x4c, 0x4b, 0x47, 0x40, 0x46, 0x45, 0x50,
32 0x5a, 0x73, 0x62, 0x50, 0x55, 0x6d, 0x56, 0x45, 0x46, 0x64, 0x88, 0x65,
33 0x6d, 0x77, 0x7b, 0x81, 0x82, 0x81, 0x4e, 0x60, 0x8d, 0x97, 0x8c, 0x7d,
34 0x96, 0x73, 0x7e, 0x81, 0x7c, 0xff, 0xc0, 0x00, 0x0b, 0x08, 0x00, 0x40,
35 0x00, 0x40, 0x01, 0x01, 0x11, 0x00, 0xff, 0xc4, 0x00, 0x1b, 0x00, 0x00,
36 0x03, 0x01, 0x01, 0x01, 0x01, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
37 0x00, 0x00, 0x00, 0x00, 0x05, 0x06, 0x04, 0x03, 0x07, 0x02, 0x01, 0xff,
38 0xc4, 0x00, 0x2f, 0x10, 0x00, 0x01, 0x03, 0x03, 0x02, 0x05, 0x03, 0x03,
39 0x03, 0x05, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x02, 0x03, 0x11,
40 0x00, 0x04, 0x05, 0x21, 0x31, 0x06, 0x12, 0x41, 0x51, 0x81, 0x61, 0x71,
41 0x91, 0x13, 0x32, 0xa1, 0x14, 0x22, 0xc1, 0x15, 0x23, 0x52, 0xd1, 0xf0,
42 0xff, 0xda, 0x00, 0x08, 0x01, 0x01, 0x00, 0x00, 0x3f, 0x00, 0xb3, 0xa2,
43 0x8a, 0x28, 0xa2, 0x8a, 0x28, 0xa2, 0x97, 0x64, 0x72, 0xd6, 0x58, 0xd4,
44 0x8f, 0xd5, 0x3d, 0xca, 0xa5, 0x7d, 0xa8, 0x4e, 0xaa, 0x3e, 0xb0, 0x3a,
45 0x7a, 0x9d, 0x2b, 0x2d, 0x87, 0x13, 0xe3, 0xaf, 0x9f, 0x0c, 0xb6, 0xb5,
46 0xb6, 0xe2, 0xb4, 0x48, 0x71, 0x30, 0x14, 0x7b, 0x02, 0x09, 0x14, 0xee,
47 0x94, 0x64, 0x38, 0x87, 0x1f, 0x8d, 0x5f, 0xd3, 0x7d, 0xe2, 0xa7, 0x46,
48 0xe8, 0x6c, 0x49, 0x1e, 0xfd, 0x07, 0xb1, 0x33, 0x5f, 0xb8, 0xdc, 0xf5,
49 0x96, 0x51, 0x7c, 0x96, 0xee, 0x14, 0xba, 0x04, 0xf2, 0x2c, 0x42, 0xa3,
50 0xd3, 0x70, 0x7c, 0x1a, 0x6d, 0x45, 0x2c, 0xcd, 0xe5, 0x11, 0x89, 0xb1,
51 0x5b, 0xc4, 0x02, 0xe1, 0xd1, 0xb4, 0xcf, 0xdc, 0xa3, 0xfc, 0x0d, 0xcd,
52 0x41, 0xde, 0xe3, 0xb2, 0x2e, 0xda, 0x1c, 0xbd, 0xe2, 0x4a, 0x90, 0xe9,
53 0x04, 0x95, 0x2b, 0xf7, 0x41, 0xd0, 0x18, 0xe8, 0x36, 0x03, 0xc6, 0x91,
54 0x4a, 0x81, 0x20, 0x82, 0x24, 0x10, 0x66, 0x45, 0x5a, 0xdd, 0xf1, 0x32,
55 0xff, 0x00, 0xa2, 0x5a, 0x8b, 0x62, 0x57, 0x7d, 0x70, 0x80, 0x93, 0x1a,
56 0x94, 0x10, 0x79, 0x4a, 0xa3, 0xb9, 0x20, 0xc0, 0xf3, 0xd3, 0x55, 0x59,
57 0x4e, 0x1c, 0x7a, 0xc7, 0x12, 0x9b, 0xc7, 0x94, 0xa7, 0x2e, 0x14, 0xa9,
58 0x74, 0x0d, 0x42, 0x01, 0x04, 0xc9, 0x3b, 0x93, 0x30, 0x09, 0xdb, 0x5f,
59 0x35, 0x9b, 0x85, 0xad, 0xde, 0x7f, 0x39, 0x6e, 0xa6, 0x82, 0xa1, 0xa5,
60 0x73, 0x2d, 0x40, 0x68, 0x13, 0x06, 0x67, 0xdf, 0x6f, 0x35, 0xe9, 0xb4,
61 0x52, 0x4c, 0xbe, 0x0c, 0x65, 0x72, 0x16, 0xcf, 0x3a, 0xff, 0x00, 0xf6,
62 0x5a, 0xd1, 0x4d, 0x11, 0xa1, 0x13, 0x26, 0x0f, 0x73, 0x00, 0x1f, 0x41,
63 0x5b, 0x72, 0xd6, 0xa2, 0xeb, 0x15, 0x73, 0x6e, 0x13, 0xf7, 0x36, 0x42,
64 0x40, 0xee, 0x04, 0x8f, 0xc8, 0x15, 0xe4, 0xf5, 0x59, 0xc1, 0x16, 0x0d,
65 0x3d, 0x70, 0xed, 0xdb, 0x84, 0x29, 0x6c, 0x40, 0x42, 0x3b, 0x13, 0x3f,
66 0xb8, 0xfc, 0x10, 0x3c, 0xd5, 0xc1, 0x00, 0x88, 0x22, 0x41, 0xef, 0x5f,
67 0x0d, 0xb4, 0x86, 0x81, 0x0d, 0xa1, 0x28, 0x07, 0x52, 0x12, 0x00, 0x06,
68 0xba, 0xd1, 0x45, 0x71, 0xb8, 0xb8, 0x6e, 0xd9, 0x85, 0xbc, 0xf2, 0xb9,
69 0x5b, 0x40, 0x25, 0x47, 0xb0, 0xaf, 0x24, 0x79, 0x48, 0x53, 0xce, 0x29,
70 0xb4, 0x94, 0xa0, 0xa8, 0x94, 0xa7, 0xb0, 0x27, 0x41, 0xf1, 0x54, 0x9c,
71 0x09, 0x71, 0xc9, 0x92, 0x7d, 0x82, 0x74, 0x75, 0xa9, 0x1e, 0xa5, 0x27,
72 0xfd, 0x13, 0x55, 0xd9, 0x3c, 0x83, 0x38, 0xbb, 0x45, 0x5c, 0xbf, 0x3c,
73 0xa1, 0x40, 0x40, 0x02, 0x54, 0x4f, 0x41, 0x3e, 0x4f, 0x83, 0x5a, 0x2d,
74 0xae, 0x1b, 0xba, 0xb7, 0x6d, 0xf6, 0x89, 0x28, 0x71, 0x21, 0x49, 0x24,
75 0x41, 0x83, 0xe9, 0x5d, 0xe9, 0x3f, 0x12, 0x64, 0x97, 0x8b, 0xc6, 0x17,
76 0x59, 0x03, 0xea, 0xa9, 0x61, 0x08, 0x24, 0x48, 0x04, 0xc9, 0x9f, 0x80,
77 0x6a, 0x4b, 0x17, 0xc4, 0xd7, 0xac, 0xdf, 0x36, 0xab, 0xbb, 0x85, 0x39,
78 0x6e, 0xb5, 0x00, 0xe0, 0x50, 0x06, 0x01, 0x3a, 0x91, 0x02, 0x44, 0x6f,
79 0x02, 0xb7, 0x65, 0xb2, 0x0e, 0x71, 0x25, 0xf3, 0x58, 0xdc, 0x72, 0x8f,
80 0xe9, 0xc1, 0xe6, 0x52, 0xe0, 0xc2, 0xa3, 0x72, 0x46, 0xe0, 0x0e, 0x83,
81 0xa9, 0xf1, 0x4b, 0x38, 0x9f, 0x16, 0xde, 0x2e, 0xfd, 0xa4, 0x32, 0x92,
82 0x1a, 0x5b, 0x40, 0x83, 0xdc, 0x8d, 0x0f, 0x9d, 0x01, 0x3e, 0xf5, 0x83,
83 0x17, 0x7a, 0xac, 0x76, 0x41, 0x9b, 0xa4, 0xa7, 0x9b, 0xe9, 0xab, 0x51,
84 0x31, 0x20, 0x82, 0x08, 0xf8, 0x34, 0xf9, 0xdb, 0x97, 0xb8, 0xb7, 0x2c,
85 0xcd, 0xba, 0x12, 0xa6, 0xec, 0xda, 0x3c, 0xca, 0x13, 0x24, 0x0e, 0xa4,
86 0x91, 0xa4, 0x9d, 0x87, 0x69, 0xf7, 0xab, 0x74, 0x21, 0x2d, 0xa1, 0x28,
87 0x4a, 0x42, 0x52, 0x90, 0x02, 0x40, 0xd8, 0x01, 0xb0, 0xae, 0x95, 0x87,
88 0x29, 0x8f, 0x6f, 0x27, 0x64, 0xe5, 0xb3, 0xc4, 0x80, 0xa8, 0x29, 0x50,
89 0xdd, 0x24, 0x6c, 0x47, 0xfd, 0xd4, 0xd4, 0x92, 0x78, 0x1e, 0xef, 0xeb,
90 0x42, 0xae, 0x98, 0x0d, 0x7f, 0x90, 0x0a, 0x27, 0xe2, 0x00, 0xfc, 0xd5,
91 0x4e, 0x27, 0x11, 0x6d, 0x89, 0x60, 0xb7, 0x6e, 0x92, 0x54, 0xa8, 0xe6,
92 0x71, 0x5b, 0xa8, 0xff, 0x00, 0x03, 0xd2, 0xbe, 0x73, 0x38, 0x86, 0x72,
93 0xf6, 0xc1, 0xb7, 0x4f, 0x2a, 0xd1, 0x25, 0x0e, 0x01, 0x25, 0x27, 0xae,
94 0x9d, 0x41, 0xed, 0xed, 0x52, 0xe8, 0xe0, 0x7b, 0xcf, 0xab, 0x0e, 0x5d,
95 0x30, 0x96, 0xe7, 0xee, 0x4f, 0x31, 0x57, 0xc1, 0x00, 0x7e, 0x6a, 0xaf,
96 0x15, 0x8b, 0x63, 0x17, 0x6e, 0x1a, 0x61, 0x24, 0x92, 0x65, 0x6b, 0x3b,
97 0xa8, 0xf7, 0x3e, 0x9d, 0x87, 0x4a, 0x63, 0x45, 0x14, 0x51, 0x45, 0x14,
98 0x51, 0x45, 0x7f, 0xff, 0xd9
99 };
100
101 /* length of data in image_jpg */
102 static const unsigned int image_jpg_len = sizeof(image_jpg);
103
104 /* dimensions of image */
105 static const unsigned int image_jpg_x = 64;
106 static const unsigned int image_jpg_y = 64;
107
108 /* start of JPEG image data section */
109 static const unsigned int image_data_offset = 20;
110 #define image_data_len (image_jpg_len - image_data_offset)
111
112 /* raw EXIF header data */
113 static const unsigned char exif_header[] = {
114 0xff, 0xd8, 0xff, 0xe1
115 };
116 /* length of data in exif_header */
117 static const unsigned int exif_header_len = sizeof(exif_header);
118
119 /* byte order to use in the EXIF block */
120 #define FILE_BYTE_ORDER EXIF_BYTE_ORDER_INTEL
121
122 /* comment to write into the EXIF block */
123 #define FILE_COMMENT "libexif demonstration image"
124
125 /* special header required for EXIF_TAG_USER_COMMENT */
126 #define ASCII_COMMENT "ASCII\0\0\0"
127
128
129 /* Get an existing tag, or create one if it doesn't exist */
init_tag(ExifData * exif,ExifIfd ifd,ExifTag tag)130 static ExifEntry *init_tag(ExifData *exif, ExifIfd ifd, ExifTag tag)
131 {
132 ExifEntry *entry;
133 /* Return an existing tag if one exists */
134 if (!((entry = exif_content_get_entry (exif->ifd[ifd], tag)))) {
135 /* Allocate a new entry */
136 entry = exif_entry_new ();
137 assert(entry != NULL); /* catch an out of memory condition */
138 entry->tag = tag; /* tag must be set before calling
139 exif_content_add_entry */
140
141 /* Attach the ExifEntry to an IFD */
142 exif_content_add_entry (exif->ifd[ifd], entry);
143
144 /* Allocate memory for the entry and fill with default data */
145 exif_entry_initialize (entry, tag);
146
147 /* Ownership of the ExifEntry has now been passed to the IFD.
148 * One must be very careful in accessing a structure after
149 * unref'ing it; in this case, we know "entry" won't be freed
150 * because the reference count was bumped when it was added to
151 * the IFD.
152 */
153 exif_entry_unref(entry);
154 }
155 return entry;
156 }
157
158 /* Create a brand-new tag with a data field of the given length, in the
159 * given IFD. This is needed when exif_entry_initialize() isn't able to create
160 * this type of tag itself, or the default data length it creates isn't the
161 * correct length.
162 */
create_tag(ExifData * exif,ExifIfd ifd,ExifTag tag,size_t len)163 static ExifEntry *create_tag(ExifData *exif, ExifIfd ifd, ExifTag tag, size_t len)
164 {
165 void *buf;
166 ExifEntry *entry;
167
168 /* Create a memory allocator to manage this ExifEntry */
169 ExifMem *mem = exif_mem_new_default();
170 assert(mem != NULL); /* catch an out of memory condition */
171
172 /* Create a new ExifEntry using our allocator */
173 entry = exif_entry_new_mem (mem);
174 assert(entry != NULL);
175
176 /* Allocate memory to use for holding the tag data */
177 buf = exif_mem_alloc(mem, len);
178 assert(buf != NULL);
179
180 /* Fill in the entry */
181 entry->data = buf;
182 entry->size = len;
183 entry->tag = tag;
184 entry->components = len;
185 entry->format = EXIF_FORMAT_UNDEFINED;
186
187 /* Attach the ExifEntry to an IFD */
188 exif_content_add_entry (exif->ifd[ifd], entry);
189
190 /* The ExifMem and ExifEntry are now owned elsewhere */
191 exif_mem_unref(mem);
192 exif_entry_unref(entry);
193
194 return entry;
195 }
196
main(void)197 int main (void)
198 {
199 int rc = 1;
200 FILE *f;
201 unsigned char *exif_data;
202 unsigned int exif_data_len;
203 ExifEntry *entry;
204 ExifData *exif = exif_data_new();
205 if (!exif) {
206 fprintf(stderr, "Out of memory\n");
207 return 2;
208 }
209
210 /* Set the image options */
211 exif_data_set_option(exif, EXIF_DATA_OPTION_FOLLOW_SPECIFICATION);
212 exif_data_set_data_type(exif, EXIF_DATA_TYPE_COMPRESSED);
213 exif_data_set_byte_order(exif, FILE_BYTE_ORDER);
214
215 /* Create the mandatory EXIF fields with default data */
216 exif_data_fix(exif);
217
218 /* All these tags are created with default values by exif_data_fix() */
219 /* Change the data to the correct values for this image. */
220 entry = init_tag(exif, EXIF_IFD_EXIF, EXIF_TAG_PIXEL_X_DIMENSION);
221 exif_set_long(entry->data, FILE_BYTE_ORDER, image_jpg_x);
222
223 entry = init_tag(exif, EXIF_IFD_EXIF, EXIF_TAG_PIXEL_Y_DIMENSION);
224 exif_set_long(entry->data, FILE_BYTE_ORDER, image_jpg_y);
225
226 entry = init_tag(exif, EXIF_IFD_EXIF, EXIF_TAG_COLOR_SPACE);
227 exif_set_short(entry->data, FILE_BYTE_ORDER, 1);
228
229 /* Create a EXIF_TAG_USER_COMMENT tag. This one must be handled
230 * differently because that tag isn't automatically created and
231 * allocated by exif_data_fix(), nor can it be created using
232 * exif_entry_initialize() so it must be explicitly allocated here.
233 */
234 entry = create_tag(exif, EXIF_IFD_EXIF, EXIF_TAG_USER_COMMENT,
235 sizeof(ASCII_COMMENT) + sizeof(FILE_COMMENT) - 2);
236 /* Write the special header needed for a comment tag */
237 memcpy(entry->data, ASCII_COMMENT, sizeof(ASCII_COMMENT)-1);
238 /* Write the actual comment text, without the trailing NUL character */
239 memcpy(entry->data+8, FILE_COMMENT, sizeof(FILE_COMMENT)-1);
240 /* create_tag() happens to set the format and components correctly for
241 * EXIF_TAG_USER_COMMENT, so there is nothing more to do. */
242
243 /* Create a EXIF_TAG_SUBJECT_AREA tag */
244 entry = create_tag(exif, EXIF_IFD_EXIF, EXIF_TAG_SUBJECT_AREA,
245 4 * exif_format_get_size(EXIF_FORMAT_SHORT));
246 entry->format = EXIF_FORMAT_SHORT;
247 entry->components = 4;
248 exif_set_short(entry->data, FILE_BYTE_ORDER, image_jpg_x / 2);
249 exif_set_short(entry->data+2, FILE_BYTE_ORDER, image_jpg_y / 2);
250 exif_set_short(entry->data+4, FILE_BYTE_ORDER, image_jpg_x);
251 exif_set_short(entry->data+6, FILE_BYTE_ORDER, image_jpg_y);
252
253 /* Get a pointer to the EXIF data block we just created */
254 exif_data_save_data(exif, &exif_data, &exif_data_len);
255 assert(exif_data != NULL);
256
257 f = fopen(FILE_NAME, "wb");
258 if (!f) {
259 fprintf(stderr, "Error creating file %s\n", FILE_NAME);
260 exif_data_unref(exif);
261 return rc;
262 }
263 /* Write EXIF header */
264 if (fwrite(exif_header, exif_header_len, 1, f) != 1) {
265 fprintf(stderr, "Error writing to file %s\n", FILE_NAME);
266 goto errout;
267 }
268 /* Write EXIF block length in big-endian order */
269 if (fputc((exif_data_len+2) >> 8, f) < 0) {
270 fprintf(stderr, "Error writing to file %s\n", FILE_NAME);
271 goto errout;
272 }
273 if (fputc((exif_data_len+2) & 0xff, f) < 0) {
274 fprintf(stderr, "Error writing to file %s\n", FILE_NAME);
275 goto errout;
276 }
277 /* Write EXIF data block */
278 if (fwrite(exif_data, exif_data_len, 1, f) != 1) {
279 fprintf(stderr, "Error writing to file %s\n", FILE_NAME);
280 goto errout;
281 }
282 /* Write JPEG image data, skipping the non-EXIF header */
283 if (fwrite(image_jpg+image_data_offset, image_data_len, 1, f) != 1) {
284 fprintf(stderr, "Error writing to file %s\n", FILE_NAME);
285 goto errout;
286 }
287 printf("Wrote file %s\n", FILE_NAME);
288 rc = 0;
289
290 errout:
291 if (fclose(f)) {
292 fprintf(stderr, "Error writing to file %s\n", FILE_NAME);
293 rc = 1;
294 }
295 /* The allocator we're using for ExifData is the standard one, so use
296 * it directly to free this pointer.
297 */
298 free(exif_data);
299 exif_data_unref(exif);
300
301 return rc;
302 }
303