summaryrefslogtreecommitdiff
path: root/source/fitz/load-tiff.c
blob: 76df053a4faf499148cd57aefc1561282716e790 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
#include "mupdf/fitz.h"

#include <limits.h>
#include <assert.h>
#include <string.h>

/*
 * TIFF image loader. Should be enough to support TIFF files in XPS.
 * Baseline TIFF 6.0 plus CMYK, LZW, Flate and JPEG support.
 * Limited bit depths (1,2,4,8).
 * Limited planar configurations (1=chunky).
 * TODO: RGBPal images
 */

struct tiff
{
	/* "file" */
	unsigned char *bp, *rp, *ep;

	/* byte order */
	unsigned order;

	/* offset of first ifd */
	unsigned ifd_offset;

	/* where we can find the strips of image data */
	unsigned rowsperstrip;
	unsigned *stripoffsets;
	unsigned *stripbytecounts;
	unsigned stripoffsetslen;
	unsigned stripbytecountslen;

	/* where we can find the tiles of image data */
	unsigned tilelength;
	unsigned tilewidth;
	unsigned *tileoffsets;
	unsigned *tilebytecounts;
	unsigned tileoffsetslen;
	unsigned tilebytecountslen;

	/* colormap */
	unsigned *colormap;
	unsigned colormaplen;

	/* assorted tags */
	unsigned subfiletype;
	unsigned photometric;
	unsigned compression;
	unsigned imagewidth;
	unsigned imagelength;
	unsigned samplesperpixel;
	unsigned bitspersample;
	unsigned planar;
	unsigned extrasamples;
	unsigned xresolution;
	unsigned yresolution;
	unsigned resolutionunit;
	unsigned fillorder;
	unsigned g3opts;
	unsigned g4opts;
	unsigned predictor;

	unsigned ycbcrsubsamp[2];

	unsigned char *jpegtables; /* point into "file" buffer */
	unsigned jpegtableslen;

	unsigned char *profile;
	int profilesize;

	/* decoded data */
	fz_colorspace *colorspace;
	unsigned char *samples;
	unsigned char *data;
	int tilestride;
	int stride;
};

enum
{
	TII = 0x4949, /* 'II' */
	TMM = 0x4d4d, /* 'MM' */
	TBYTE = 1,
	TASCII = 2,
	TSHORT = 3,
	TLONG = 4,
	TRATIONAL = 5
};

#define NewSubfileType 254
#define ImageWidth 256
#define ImageLength 257
#define BitsPerSample 258
#define Compression 259
#define PhotometricInterpretation 262
#define FillOrder 266
#define StripOffsets 273
#define SamplesPerPixel 277
#define RowsPerStrip 278
#define StripByteCounts 279
#define XResolution 282
#define YResolution 283
#define PlanarConfiguration 284
#define T4Options 292
#define T6Options 293
#define ResolutionUnit 296
#define Predictor 317
#define ColorMap 320
#define TileWidth 322
#define TileLength 323
#define TileOffsets 324
#define TileByteCounts 325
#define ExtraSamples 338
#define JPEGTables 347
#define YCbCrSubSampling 530
#define ICCProfile 34675

static const unsigned char bitrev[256] =
{
	0x00, 0x80, 0x40, 0xc0, 0x20, 0xa0, 0x60, 0xe0,
	0x10, 0x90, 0x50, 0xd0, 0x30, 0xb0, 0x70, 0xf0,
	0x08, 0x88, 0x48, 0xc8, 0x28, 0xa8, 0x68, 0xe8,
	0x18, 0x98, 0x58, 0xd8, 0x38, 0xb8, 0x78, 0xf8,
	0x04, 0x84, 0x44, 0xc4, 0x24, 0xa4, 0x64, 0xe4,
	0x14, 0x94, 0x54, 0xd4, 0x34, 0xb4, 0x74, 0xf4,
	0x0c, 0x8c, 0x4c, 0xcc, 0x2c, 0xac, 0x6c, 0xec,
	0x1c, 0x9c, 0x5c, 0xdc, 0x3c, 0xbc, 0x7c, 0xfc,
	0x02, 0x82, 0x42, 0xc2, 0x22, 0xa2, 0x62, 0xe2,
	0x12, 0x92, 0x52, 0xd2, 0x32, 0xb2, 0x72, 0xf2,
	0x0a, 0x8a, 0x4a, 0xca, 0x2a, 0xaa, 0x6a, 0xea,
	0x1a, 0x9a, 0x5a, 0xda, 0x3a, 0xba, 0x7a, 0xfa,
	0x06, 0x86, 0x46, 0xc6, 0x26, 0xa6, 0x66, 0xe6,
	0x16, 0x96, 0x56, 0xd6, 0x36, 0xb6, 0x76, 0xf6,
	0x0e, 0x8e, 0x4e, 0xce, 0x2e, 0xae, 0x6e, 0xee,
	0x1e, 0x9e, 0x5e, 0xde, 0x3e, 0xbe, 0x7e, 0xfe,
	0x01, 0x81, 0x41, 0xc1, 0x21, 0xa1, 0x61, 0xe1,
	0x11, 0x91, 0x51, 0xd1, 0x31, 0xb1, 0x71, 0xf1,
	0x09, 0x89, 0x49, 0xc9, 0x29, 0xa9, 0x69, 0xe9,
	0x19, 0x99, 0x59, 0xd9, 0x39, 0xb9, 0x79, 0xf9,
	0x05, 0x85, 0x45, 0xc5, 0x25, 0xa5, 0x65, 0xe5,
	0x15, 0x95, 0x55, 0xd5, 0x35, 0xb5, 0x75, 0xf5,
	0x0d, 0x8d, 0x4d, 0xcd, 0x2d, 0xad, 0x6d, 0xed,
	0x1d, 0x9d, 0x5d, 0xdd, 0x3d, 0xbd, 0x7d, 0xfd,
	0x03, 0x83, 0x43, 0xc3, 0x23, 0xa3, 0x63, 0xe3,
	0x13, 0x93, 0x53, 0xd3, 0x33, 0xb3, 0x73, 0xf3,
	0x0b, 0x8b, 0x4b, 0xcb, 0x2b, 0xab, 0x6b, 0xeb,
	0x1b, 0x9b, 0x5b, 0xdb, 0x3b, 0xbb, 0x7b, 0xfb,
	0x07, 0x87, 0x47, 0xc7, 0x27, 0xa7, 0x67, 0xe7,
	0x17, 0x97, 0x57, 0xd7, 0x37, 0xb7, 0x77, 0xf7,
	0x0f, 0x8f, 0x4f, 0xcf, 0x2f, 0xaf, 0x6f, 0xef,
	0x1f, 0x9f, 0x5f, 0xdf, 0x3f, 0xbf, 0x7f, 0xff
};

static inline int tiff_getcomp(unsigned char *line, int x, int bpc)
{
	switch (bpc)
	{
	case 1: return (line[x >> 3] >> ( 7 - (x & 7) ) ) & 1;
	case 2: return (line[x >> 2] >> ( ( 3 - (x & 3) ) << 1 ) ) & 3;
	case 4: return (line[x >> 1] >> ( ( 1 - (x & 1) ) << 2 ) ) & 15;
	case 8: return line[x];
	case 16: return line[x << 1] << 8 | line[(x << 1) + 1];
	}
	return 0;
}

static inline void tiff_putcomp(unsigned char *line, int x, int bpc, int value)
{
	int maxval = (1 << bpc) - 1;

	switch (bpc)
	{
	case 1: line[x >> 3] &= ~(maxval << (7 - (x & 7))); break;
	case 2: line[x >> 2] &= ~(maxval << ((3 - (x & 3)) << 1)); break;
	case 4: line[x >> 1] &= ~(maxval << ((1 - (x & 1)) << 2)); break;
	}

	switch (bpc)
	{
	case 1: line[x >> 3] |= value << (7 - (x & 7)); break;
	case 2: line[x >> 2] |= value << ((3 - (x & 3)) << 1); break;
	case 4: line[x >> 1] |= value << ((1 - (x & 1)) << 2); break;
	case 8: line[x] = value; break;
	case 16: line[x << 1] = value >> 8; line[(x << 1) + 1] = value & 0xFF; break;
	}
}

static void
tiff_unpredict_line(unsigned char *line, int width, int comps, int bits)
{
	unsigned char left[32];
	int i, k, v;

	for (k = 0; k < comps; k++)
		left[k] = 0;

	for (i = 0; i < width; i++)
	{
		for (k = 0; k < comps; k++)
		{
			v = tiff_getcomp(line, i * comps + k, bits);
			v = v + left[k];
			v = v % (1 << bits);
			tiff_putcomp(line, i * comps + k, bits, v);
			left[k] = v;
		}
	}
}

static void
tiff_invert_line(unsigned char *line, int width, int comps, int bits, int alpha)
{
	int i, k, v;
	int m = (1 << bits) - 1;

	for (i = 0; i < width; i++)
	{
		for (k = 0; k < comps; k++)
		{
			v = tiff_getcomp(line, i * comps + k, bits);
			if (!alpha || k < comps - 1)
				v = m - v;
			tiff_putcomp(line, i * comps + k, bits, v);
		}
	}
}

static void
tiff_expand_colormap(fz_context *ctx, struct tiff *tiff)
{
	int maxval = 1 << tiff->bitspersample;
	unsigned char *samples;
	unsigned char *src, *dst;
	unsigned int x, y;
	unsigned int stride;

	/* colormap has first all red, then all green, then all blue values */
	/* colormap values are 0..65535, bits is 4 or 8 */
	/* image can be with or without extrasamples: comps is 1 or 2 */

	if (tiff->samplesperpixel != 1 && tiff->samplesperpixel != 2)
		fz_throw(ctx, FZ_ERROR_GENERIC, "invalid number of samples for RGBPal");

	if (tiff->bitspersample != 1 && tiff->bitspersample != 2 && tiff->bitspersample != 4 && tiff->bitspersample != 8 && tiff->bitspersample != 16)
		fz_throw(ctx, FZ_ERROR_GENERIC, "invalid number of bits for RGBPal");

	if (tiff->colormaplen < (unsigned)maxval * 3)
		fz_throw(ctx, FZ_ERROR_GENERIC, "insufficient colormap data");

	if (tiff->imagelength > UINT_MAX / tiff->imagewidth / (tiff->samplesperpixel + 2))
		fz_throw(ctx, FZ_ERROR_GENERIC, "image too large");

	stride = tiff->imagewidth * (tiff->samplesperpixel + 2);

	samples = fz_malloc(ctx, stride * tiff->imagelength);

	for (y = 0; y < tiff->imagelength; y++)
	{
		src = tiff->samples + (unsigned int)(tiff->stride * y);
		dst = samples + (unsigned int)(stride * y);

		for (x = 0; x < tiff->imagewidth; x++)
		{
			if (tiff->extrasamples)
			{
				int c = tiff_getcomp(src, x * 2, tiff->bitspersample);
				int a = tiff_getcomp(src, x * 2 + 1, tiff->bitspersample);
				*dst++ = tiff->colormap[c + 0] >> 8;
				*dst++ = tiff->colormap[c + maxval] >> 8;
				*dst++ = tiff->colormap[c + maxval * 2] >> 8;
				*dst++ = a << (8 - tiff->bitspersample);
			}
			else
			{
				int c = tiff_getcomp(src, x, tiff->bitspersample);
				*dst++ = tiff->colormap[c + 0] >> 8;
				*dst++ = tiff->colormap[c + maxval] >> 8;
				*dst++ = tiff->colormap[c + maxval * 2] >> 8;
			}
		}
	}

	tiff->samplesperpixel += 2;
	tiff->bitspersample = 8;
	tiff->stride = stride;
	fz_free(ctx, tiff->samples);
	tiff->samples = samples;
}

static unsigned
tiff_decode_data(fz_context *ctx, struct tiff *tiff, unsigned char *rp, unsigned int rlen, unsigned char *wp, unsigned int wlen)
{
	fz_stream *encstm = NULL;
	fz_stream *stm = NULL;
	unsigned i, size = 0;
	unsigned char *reversed = NULL;
	fz_stream *jpegtables = NULL;
	int old_tiff;

	if (rp + rlen > tiff->ep)
		fz_throw(ctx, FZ_ERROR_GENERIC, "strip extends beyond the end of the file");

	/* the bits are in un-natural order */
	if (tiff->fillorder == 2)
	{
		reversed = fz_malloc(ctx, rlen);
		for (i = 0; i < rlen; i++)
			reversed[i] = bitrev[rp[i]];
		rp = reversed;
	}

	fz_var(encstm);
	fz_var(stm);

	fz_try(ctx)
	{
		/* each decoder will close this */
		encstm = fz_open_memory(ctx, rp, rlen);

		/* switch on compression to create a filter */
		/* feed each chunk (strip or tile) to the filter */
		/* read out the data into a buffer */
		/* the level above packs the chunk's samples into a pixmap */

		/* type 32773 / packbits -- nothing special (same row-padding as PDF) */
		/* type 2 / ccitt rle -- no EOL, no RTC, rows are byte-aligned */
		/* type 3 and 4 / g3 and g4 -- each strip starts new section */
		/* type 5 / lzw -- each strip is handled separately */

		switch (tiff->compression)
		{
		case 1:
			/* stm already open and reading uncompressed data */
			stm = encstm;
			break;
		case 2:
		case 3:
		case 4:
			stm = fz_open_faxd(ctx, encstm,
					tiff->compression == 4 ? -1 :
					tiff->compression == 2 ? 0 :
					tiff->g3opts & 1,
					0,
					tiff->compression == 2,
					tiff->imagewidth,
					tiff->imagelength,
					0,
					1);
			break;
		case 5:
			old_tiff = rp[0] == 0 && (rp[1] & 1);
			stm = fz_open_lzwd(ctx, encstm, old_tiff ? 0 : 1, 9, old_tiff ? 1 : 0, old_tiff);
			break;
		case 6:
			fz_warn(ctx, "deprecated JPEG in TIFF compression not fully supported");
			/* fall through */
		case 7:
			if (tiff->jpegtables && (int)tiff->jpegtableslen > 0)
				jpegtables = fz_open_memory(ctx, tiff->jpegtables, tiff->jpegtableslen);

			stm = fz_open_dctd(ctx, encstm,
					tiff->photometric == 2 || tiff->photometric == 3 ? 0 : -1,
					0,
					jpegtables);
			break;
		case 8:
		case 32946:
			stm = fz_open_flated(ctx, encstm, 15);
			break;
		case 32773:
			stm = fz_open_rld(ctx, encstm);
			break;
		case 34676:
			if (tiff->photometric == 32845)
				stm = fz_open_sgilog32(ctx, encstm, tiff->imagewidth);
			else
				stm = fz_open_sgilog16(ctx, encstm, tiff->imagewidth);
			break;
		case 34677:
			stm = fz_open_sgilog24(ctx, encstm, tiff->imagewidth);
			break;
		case 32809:
			if (tiff->bitspersample != 4)
				fz_throw(ctx, FZ_ERROR_GENERIC, "invalid bits per pixel in thunder encoding");
			stm = fz_open_thunder(ctx, encstm, tiff->imagewidth);
			break;
		default:
			stm = encstm;
			fz_throw(ctx, FZ_ERROR_GENERIC, "unknown TIFF compression: %d", tiff->compression);
		}

		size = (unsigned)fz_read(ctx, stm, wp, wlen);
	}
	fz_always(ctx)
	{
		fz_drop_stream(ctx, stm);
		fz_free(ctx, reversed);
	}
	fz_catch(ctx)
		fz_rethrow(ctx);

	return size;
}

static void
tiff_paste_tile(fz_context *ctx, struct tiff *tiff, unsigned char *tile, unsigned int row, unsigned int col)
{
	unsigned int x, y, k;

	for (y = 0; y < tiff->tilelength && row + y < tiff->imagelength; y++)
	{
		for (x = 0; x < tiff->tilewidth && col + x < tiff->imagewidth; x++)
		{
			for (k = 0; k < tiff->samplesperpixel; k++)
			{
				unsigned char *dst, *src;

				dst = tiff->samples;
				dst += (row + y) * tiff->stride;
				dst += (((col + x) * tiff->samplesperpixel + k) * tiff->bitspersample + 7) / 8;

				src = tile;
				src += y * tiff->tilestride;
				src += ((x * tiff->samplesperpixel + k) * tiff->bitspersample + 7) / 8;

				switch (tiff->bitspersample)
				{
				case 1: *dst |= (*src >> (7 - 1 * ((col + x) % 8))) & 0x1; break;
				case 2: *dst |= (*src >> (6 - 2 * ((col + x) % 4))) & 0x3; break;
				case 4: *dst |= (*src >> (4 - 4 * ((col + x) % 2))) & 0xf; break;
				case 8: *dst = *src; break;
				case 16: dst[0] = src[0]; dst[1] = src[1]; break;
				}
			}
		}
	}
}

static void
tiff_paste_subsampled_tile(fz_context *ctx, struct tiff *tiff, unsigned char *tile, unsigned len, unsigned tw, unsigned th, unsigned col, unsigned row)
{
	/*
	This explains how the samples are laid out in tiff data, the spec example is non-obvious.
	The y, cb, cr indicies follow the spec, i.e. y17 is the y sample at row 1, column 7.
	All indicies start at 0.

	hexlookup = (horizontalsubsampling & 0xf) << 4 | (verticalsubsampling & 0xf)

	0x11	y00 cb00 cr00	0x21	y00 y01 cb00 cr00	0x41	y00 y01 y02 y03 cb00 cr00
		y01 cb01 cr01		y10 y11 cb01 cr01		y04 y05 y06 y07 cb01 cr01
		....			...				...
		y10 cb10 cr10		y20 y21 cb10 cr10		y10 y11 y12 y13 cb10 cr10
		y11 cb11 cr11		y30 y31 cb11 cr11		y14 y15 y16 y17 cb11 cr11

	0x12	y00		0x22	y00 y01			0x42	y00 y01 y02 y03
		y10 cb00 cr00		y10 y11 cb00 cr00		y10 y11 y12 y13 cb00 cr00
		y01			y02 y03				y04 y05 y06 y07
		y11 cb01 cr01		y12 y13 cb01 cr01		y14 y15 y16 y17 cb01 cr01
		....			...				...
		y20			y20 y21				y20 y21 y22 y23
		y30 cb10 cr10		y30 y31 cb10 cr10		y30 y31 y32 y33 cb10 cr10
		y21			y22 y23				y24 y25 y26 y27
		y31 cb11 cr11		y32 y33 cb11 cr11		y34 y35 y36 y37 cb11 cr11

	0x14	y00		0x24	y00 y01			0x44	y00 y01 y02 y03
		y10			y10 y11				y10 y11 y12 y13
		y20			y20 y21				y20 y21 y22 y23
		y30 cb00 cr00		y30 y31 cb00 cr00		y30 y31 y32 y33 cb00 cr00
		y01			y02 y03				y04 y05 y06 y07
		y11			y12 y13				y14 y15 y16 y17
		y21			y22 y23				y24 y25 y26 y27
		y31 cb01 cr01		y32 y33 cb01 cr01		y34 y35 y36 y37 cb01 cr01
		....			...				...
		y40			y40 y41				y40 y41 y42 y43
		y50			y50 y51				y50 y51 y52 y53
		y60			y60 y61				y60 y61 y62 y63
		y70 cb10 cr10		y70 y71 cb10 cr10		y70 y71 y72 y73 cb10 cr10
		y41			y42 y43				y44 y45 y46 y47
		y51			y52 y53				y54 y55 y56 y57
		y61			y62 y63				y64 y65 y66 y67
		y71 cb11 cr11		y72 y73 cb11 cr11		y74 y75 y76 y77 cb11 cr11
	*/

	unsigned char *src = tile;
	unsigned char *dst;
	unsigned x, y, w, h; /* coordinates and dimensions of entire image */
	unsigned sx, sy, sw, sh; /* coordinates and dimensions of a single subsample region, i.e. max 4 x 4 samples */
	int k;
	int offsets[4 * 4 * 3]; /* for a pixel position, these point to all pixel components in a subsample region */
	int *offset = offsets;

	assert(tiff->samplesperpixel == 3);
	assert(tiff->bitspersample == 8);

	w = tiff->imagewidth;
	h = tiff->imagelength;

	sx = 0;
	sy = 0;
	sw = tiff->ycbcrsubsamp[0];
	sh = tiff->ycbcrsubsamp[1];

	for (k = 0; k < 3; k++)
		for (y = 0; y < sh; y++)
			for (x = 0; x < sw; x++)
				*offset++ = k + y * tiff->stride + x * 3;

	offset = offsets;
	x = col;
	y = row;
	k = 0;

	dst = &tiff->samples[row * tiff->stride + col * 3];

	while (src < tile + len)
	{
		if (k == 0)
		{ /* put all Y samples for a subsample region at the correct image pixel */
			if (y + sy < h && y + sy < row + th && x + sx < w && x + sx < col + tw)
				dst[*offset] = *src;
			offset++;

			if (++sx >= sw)
			{
				sx = 0;
				if (++sy >= sh)
				{
					sy = 0;
					k++;
				}
			}
		}
		else
		{ /* put all Cb/Cr samples for a subsample region at the correct image pixel */
			for (sy = 0; sy < sh; sy++)
				for (sx = 0; sx < sw; sx++)
				{
					if (y + sy < h && y + sy < row + th && x + sx < w && x + sx < col + tw)
						dst[*offset] = *src;
					offset++;
				}

			if (++k >= 3)
			{ /* we're done with this subsample region, on to the next one */
				k = sx = sy = 0;
				offset = offsets;

				dst += sw * 3;

				x += sw;
				if (x >= col + tw)
				{
					dst -= (x - (col + tw)) * 3;
					dst += (sh - 1) * w * 3;
					dst += col * 3;
					x = col;
					y += sh;
				}
			}
		}

		src++;
	}
}

static void
tiff_decode_tiles(fz_context *ctx, struct tiff *tiff)
{
	unsigned char *data;
	unsigned x, y, wlen, tile;
	unsigned tiles, tilesacross, tilesdown;

	tilesdown = (tiff->imagelength + tiff->tilelength - 1) / tiff->tilelength;
	tilesacross = (tiff->imagewidth + tiff->tilewidth - 1) / tiff->tilewidth;
	tiles = tilesacross * tilesdown;
	if (tiff->tileoffsetslen < tiles || tiff->tilebytecountslen < tiles)
		fz_throw(ctx, FZ_ERROR_GENERIC, "insufficient tile metadata");

	/* JPEG can handle subsampling on its own */
	if (tiff->photometric == 6 && tiff->compression != 6 && tiff->compression != 7)
	{
		/* regardless of how this is subsampled, a tile is never larger */
		if (tiff->tilelength >= tiff->ycbcrsubsamp[1])
			wlen = tiff->tilestride * tiff->tilelength;
		else
			wlen = tiff->tilestride * tiff->ycbcrsubsamp[1];

		data = tiff->data = fz_malloc(ctx, wlen);

		tile = 0;
		for (x = 0; x < tiff->imagelength; x += tiff->tilelength)
		{
			for (y = 0; y < tiff->imagewidth; y += tiff->tilewidth)
			{
				unsigned int offset = tiff->tileoffsets[tile];
				unsigned int rlen = tiff->tilebytecounts[tile];
				unsigned char *rp = tiff->bp + offset;
				unsigned decoded;

				if (offset > (unsigned)(tiff->ep - tiff->bp))
					fz_throw(ctx, FZ_ERROR_GENERIC, "invalid tile offset %u", offset);
				if (rlen > (unsigned)(tiff->ep - rp))
					fz_throw(ctx, FZ_ERROR_GENERIC, "invalid tile byte count %u", rlen);

				decoded = tiff_decode_data(ctx, tiff, rp, rlen, data, wlen);
				tiff_paste_subsampled_tile(ctx, tiff, data, decoded, tiff->tilewidth, tiff->tilelength, x, y);
				tile++;
			}
		}
	}
	else
	{
		wlen = tiff->tilelength * tiff->tilestride;
		data = tiff->data = fz_malloc(ctx, wlen);

		tile = 0;
		for (x = 0; x < tiff->imagelength; x += tiff->tilelength)
		{
			for (y = 0; y < tiff->imagewidth; y += tiff->tilewidth)
			{
				unsigned int offset = tiff->tileoffsets[tile];
				unsigned int rlen = tiff->tilebytecounts[tile];
				unsigned char *rp = tiff->bp + offset;

				if (offset > (unsigned)(tiff->ep - tiff->bp))
					fz_throw(ctx, FZ_ERROR_GENERIC, "invalid tile offset %u", offset);
				if (rlen > (unsigned)(tiff->ep - rp))
					fz_throw(ctx, FZ_ERROR_GENERIC, "invalid tile byte count %u", rlen);

				if (tiff_decode_data(ctx, tiff, rp, rlen, data, wlen) != wlen)
					fz_throw(ctx, FZ_ERROR_GENERIC, "decoded tile is the wrong size");

				tiff_paste_tile(ctx, tiff, data, x, y);
				tile++;
			}
		}
	}
}

static void
tiff_decode_strips(fz_context *ctx, struct tiff *tiff)
{
	unsigned char *data;
	unsigned strips;
	unsigned strip;
	unsigned y;

	strips = (tiff->imagelength + tiff->rowsperstrip - 1) / tiff->rowsperstrip;
	if (tiff->stripoffsetslen < strips || tiff->stripbytecountslen < strips)
		fz_throw(ctx, FZ_ERROR_GENERIC, "insufficient strip metadata");

	data = tiff->samples;

	/* JPEG can handle subsampling on its own */
	if (tiff->photometric == 6 && tiff->compression != 6 && tiff->compression != 7)
	{
		unsigned wlen;
		unsigned rowsperstrip;

		/* regardless of how this is subsampled, a strip is never taller */
		if (tiff->rowsperstrip >= tiff->ycbcrsubsamp[1])
			rowsperstrip = tiff->rowsperstrip;
		else
			rowsperstrip = tiff->ycbcrsubsamp[1];

		wlen = rowsperstrip * tiff->stride;
		data = tiff->data = fz_malloc(ctx, wlen);

		strip = 0;
		for (y = 0; y < tiff->imagelength; y += rowsperstrip)
		{
			unsigned offset = tiff->stripoffsets[strip];
			unsigned rlen = tiff->stripbytecounts[strip];
			unsigned char *rp = tiff->bp + offset;
			int decoded;

			if (offset > (unsigned)(tiff->ep - tiff->bp))
				fz_throw(ctx, FZ_ERROR_GENERIC, "invalid strip offset %u", offset);
			if (rlen > (unsigned)(tiff->ep - rp))
				fz_throw(ctx, FZ_ERROR_GENERIC, "invalid strip byte count %u", rlen);

			decoded = tiff_decode_data(ctx, tiff, rp, rlen, data, wlen);
			tiff_paste_subsampled_tile(ctx, tiff, data, decoded, tiff->imagewidth, tiff->rowsperstrip, 0, y);
			strip++;
		}
	}
	else
	{
		strip = 0;
		for (y = 0; y < tiff->imagelength; y += tiff->rowsperstrip)
		{
			unsigned offset = tiff->stripoffsets[strip];
			unsigned rlen = tiff->stripbytecounts[strip];
			unsigned wlen = tiff->stride * tiff->rowsperstrip;
			unsigned char *rp = tiff->bp + offset;

			if (offset > (unsigned)(tiff->ep - tiff->bp))
				fz_throw(ctx, FZ_ERROR_GENERIC, "invalid strip offset %u", offset);
			if (rlen > (unsigned)(tiff->ep - rp))
				fz_throw(ctx, FZ_ERROR_GENERIC, "invalid strip byte count %u", rlen);

			/* if imagelength is not a multiple of rowsperstrip, adjust the expectation of the size of the decoded data */
			if (y + tiff->rowsperstrip >= tiff->imagelength)
				wlen = tiff->stride * (tiff->imagelength - y);

			if (tiff_decode_data(ctx, tiff, rp, rlen, data, wlen) < wlen)
			{
				fz_warn(ctx, "premature end of data in decoded strip");
				break;
			}

			data += wlen;
			strip ++;
		}
	}
}

static inline int tiff_readbyte(struct tiff *tiff)
{
	if (tiff->rp < tiff->ep)
		return *tiff->rp++;
	return EOF;
}

static inline unsigned readshort(struct tiff *tiff)
{
	unsigned a = tiff_readbyte(tiff);
	unsigned b = tiff_readbyte(tiff);
	if (tiff->order == TII)
		return (b << 8) | a;
	return (a << 8) | b;
}

static inline unsigned tiff_readlong(struct tiff *tiff)
{
	unsigned a = tiff_readbyte(tiff);
	unsigned b = tiff_readbyte(tiff);
	unsigned c = tiff_readbyte(tiff);
	unsigned d = tiff_readbyte(tiff);
	if (tiff->order == TII)
		return (d << 24) | (c << 16) | (b << 8) | a;
	return (a << 24) | (b << 16) | (c << 8) | d;
}

static void
tiff_read_bytes(unsigned char *p, struct tiff *tiff, unsigned ofs, unsigned n)
{
	if (ofs > (unsigned)(tiff->ep - tiff->bp))
		ofs = (unsigned)(tiff->ep - tiff->bp);
	tiff->rp = tiff->bp + ofs;

	while (n--)
		*p++ = tiff_readbyte(tiff);
}

static void
tiff_read_tag_value(unsigned *p, struct tiff *tiff, unsigned type, unsigned ofs, unsigned n)
{
	unsigned den;

	if (ofs > (unsigned)(tiff->ep - tiff->bp))
		ofs = (unsigned)(tiff->ep - tiff->bp);
	tiff->rp = tiff->bp + ofs;

	while (n--)
	{
		switch (type)
		{
		case TRATIONAL:
			*p = tiff_readlong(tiff);
			den = tiff_readlong(tiff);
			if (den)
				*p = *p / den;
			else
				*p = UINT_MAX;
			p ++;
			break;
		case TBYTE: *p++ = tiff_readbyte(tiff); break;
		case TSHORT: *p++ = readshort(tiff); break;
		case TLONG: *p++ = tiff_readlong(tiff); break;
		default: *p++ = 0; break;
		}
	}
}

static void
tiff_read_tag(fz_context *ctx, struct tiff *tiff, unsigned offset)
{
	unsigned tag;
	unsigned type;
	unsigned count;
	unsigned value;

	tiff->rp = tiff->bp + offset;

	tag = readshort(tiff);
	type = readshort(tiff);
	count = tiff_readlong(tiff);

	if ((type == TBYTE && count <= 4) ||
			(type == TSHORT && count <= 2) ||
			(type == TLONG && count <= 1))
		value = tiff->rp - tiff->bp;
	else
		value = tiff_readlong(tiff);

	switch (tag)
	{
	case NewSubfileType:
		tiff_read_tag_value(&tiff->subfiletype, tiff, type, value, 1);
		break;
	case ImageWidth:
		tiff_read_tag_value(&tiff->imagewidth, tiff, type, value, 1);
		break;
	case ImageLength:
		tiff_read_tag_value(&tiff->imagelength, tiff, type, value, 1);
		break;
	case BitsPerSample:
		tiff_read_tag_value(&tiff->bitspersample, tiff, type, value, 1);
		break;
	case Compression:
		tiff_read_tag_value(&tiff->compression, tiff, type, value, 1);
		break;
	case PhotometricInterpretation:
		tiff_read_tag_value(&tiff->photometric, tiff, type, value, 1);
		break;
	case FillOrder:
		tiff_read_tag_value(&tiff->fillorder, tiff, type, value, 1);
		break;
	case SamplesPerPixel:
		tiff_read_tag_value(&tiff->samplesperpixel, tiff, type, value, 1);
		break;
	case RowsPerStrip:
		tiff_read_tag_value(&tiff->rowsperstrip, tiff, type, value, 1);
		break;
	case XResolution:
		tiff_read_tag_value(&tiff->xresolution, tiff, type, value, 1);
		break;
	case YResolution:
		tiff_read_tag_value(&tiff->yresolution, tiff, type, value, 1);
		break;
	case PlanarConfiguration:
		tiff_read_tag_value(&tiff->planar, tiff, type, value, 1);
		break;
	case T4Options:
		tiff_read_tag_value(&tiff->g3opts, tiff, type, value, 1);
		break;
	case T6Options:
		tiff_read_tag_value(&tiff->g4opts, tiff, type, value, 1);
		break;
	case Predictor:
		tiff_read_tag_value(&tiff->predictor, tiff, type, value, 1);
		break;
	case ResolutionUnit:
		tiff_read_tag_value(&tiff->resolutionunit, tiff, type, value, 1);
		break;
	case YCbCrSubSampling:
		tiff_read_tag_value(tiff->ycbcrsubsamp, tiff, type, value, 2);
		break;
	case ExtraSamples:
		tiff_read_tag_value(&tiff->extrasamples, tiff, type, value, 1);
		break;

	case ICCProfile:
		if (tiff->profile)
			fz_throw(ctx, FZ_ERROR_GENERIC, "at most one ICC profile tag allowed");
		tiff->profile = fz_malloc(ctx, count);
		/* ICC profile data type is set to UNDEFINED.
		 * TBYTE reading not correct in tiff_read_tag_value */
		tiff_read_bytes(tiff->profile, tiff, value, count);
		tiff->profilesize = count;
		break;

	case JPEGTables:
		tiff->jpegtables = tiff->bp + value;
		tiff->jpegtableslen = count;
		break;

	case StripOffsets:
		if (tiff->stripoffsets)
			fz_throw(ctx, FZ_ERROR_GENERIC, "at most one strip offsets tag allowed");
		tiff->stripoffsets = fz_malloc_array(ctx, count, sizeof(unsigned));
		tiff_read_tag_value(tiff->stripoffsets, tiff, type, value, count);
		tiff->stripoffsetslen = count;
		break;

	case StripByteCounts:
		if (tiff->stripbytecounts)
			fz_throw(ctx, FZ_ERROR_GENERIC, "at most one strip byte counts tag allowed");
		tiff->stripbytecounts = fz_malloc_array(ctx, count, sizeof(unsigned));
		tiff_read_tag_value(tiff->stripbytecounts, tiff, type, value, count);
		tiff->stripbytecountslen = count;
		break;

	case ColorMap:
		if (tiff->colormap)
			fz_throw(ctx, FZ_ERROR_GENERIC, "at most one color map allowed");
		tiff->colormap = fz_malloc_array(ctx, count, sizeof(unsigned));
		tiff_read_tag_value(tiff->colormap, tiff, type, value, count);
		tiff->colormaplen = count;
		break;

	case TileWidth:
		tiff_read_tag_value(&tiff->tilewidth, tiff, type, value, 1);
		break;

	case TileLength:
		tiff_read_tag_value(&tiff->tilelength, tiff, type, value, 1);
		break;

	case TileOffsets:
		if (tiff->tileoffsets)
			fz_throw(ctx, FZ_ERROR_GENERIC, "at most one tile offsets tag allowed");
		tiff->tileoffsets = fz_malloc_array(ctx, count, sizeof(unsigned));
		tiff_read_tag_value(tiff->tileoffsets, tiff, type, value, count);
		tiff->tileoffsetslen = count;
		break;

	case TileByteCounts:
		if (tiff->tilebytecounts)
			fz_throw(ctx, FZ_ERROR_GENERIC, "at most one tile byte counts tag allowed");
		tiff->tilebytecounts = fz_malloc_array(ctx, count, sizeof(unsigned));
		tiff_read_tag_value(tiff->tilebytecounts, tiff, type, value, count);
		tiff->tilebytecountslen = count;
		break;

	default:
		/* fz_warn(ctx, "unknown tag: %d t=%d n=%d", tag, type, count); */
		break;
	}
}

static void
tiff_swap_byte_order(unsigned char *buf, int n)
{
	int i, t;
	for (i = 0; i < n; i++)
	{
		t = buf[i * 2 + 0];
		buf[i * 2 + 0] = buf[i * 2 + 1];
		buf[i * 2 + 1] = t;
	}
}

static void
tiff_scale_lab_samples(fz_context *ctx, unsigned char *buf, int bps, int n)
{
	int i;
	if (bps == 8)
		for (i = 0; i < n; i++, buf += 3)
		{
			buf[1] ^= 128;
			buf[2] ^= 128;
		}
	else if (bps == 16)
		for (i = 0; i < n; i++, buf += 6)
		{
			buf[2] ^= 128;
			buf[4] ^= 128;
		}
}

static void
tiff_read_header(fz_context *ctx, struct tiff *tiff, unsigned char *buf, size_t len)
{
	unsigned version;

	memset(tiff, 0, sizeof(struct tiff));
	tiff->bp = buf;
	tiff->rp = buf;
	tiff->ep = buf + len;

	/* tag defaults, where applicable */
	tiff->bitspersample = 1;
	tiff->compression = 1;
	tiff->samplesperpixel = 1;
	tiff->resolutionunit = 2;
	tiff->rowsperstrip = 0xFFFFFFFF;
	tiff->fillorder = 1;
	tiff->planar = 1;
	tiff->subfiletype = 0;
	tiff->predictor = 1;
	tiff->ycbcrsubsamp[0] = 2;
	tiff->ycbcrsubsamp[1] = 2;

	/*
	 * Read IFH
	 */

	/* get byte order marker */
	tiff->order = readshort(tiff);
	if (tiff->order != TII && tiff->order != TMM)
		fz_throw(ctx, FZ_ERROR_GENERIC, "not a TIFF file, wrong magic marker");

	/* check version */
	version = readshort(tiff);
	if (version != 42)
		fz_throw(ctx, FZ_ERROR_GENERIC, "not a TIFF file, wrong version marker");

	/* get offset of IFD */
	tiff->ifd_offset = tiff_readlong(tiff);
}

static unsigned
tiff_next_ifd(fz_context *ctx, struct tiff *tiff, unsigned offset)
{
	unsigned count;

	if (offset > (unsigned)(tiff->ep - tiff->bp))
		fz_throw(ctx, FZ_ERROR_GENERIC, "invalid IFD offset %u", offset);

	tiff->rp = tiff->bp + offset;
	count = readshort(tiff);

	if (count * 12 > (unsigned)(tiff->ep - tiff->rp))
		fz_throw(ctx, FZ_ERROR_GENERIC, "overlarge IFD entry count %u", count);

	tiff->rp += count * 12;
	offset = tiff_readlong(tiff);

	return offset;
}

static void
tiff_seek_ifd(fz_context *ctx, struct tiff *tiff, int subimage)
{
	unsigned offset = tiff->ifd_offset;

	while (subimage--)
	{
		offset = tiff_next_ifd(ctx, tiff, offset);

		if (offset == 0)
			fz_throw(ctx, FZ_ERROR_GENERIC, "subimage index %i out of range", subimage);
	}

	tiff->rp = tiff->bp + offset;

	if (tiff->rp < tiff->bp || tiff->rp > tiff->ep)
		fz_throw(ctx, FZ_ERROR_GENERIC, "invalid IFD offset %u", tiff->ifd_offset);
}

static void
tiff_read_ifd(fz_context *ctx, struct tiff *tiff)
{
	unsigned offset;
	unsigned count;
	unsigned i;

	offset = tiff->rp - tiff->bp;

	count = readshort(tiff);

	if (count * 12 > (unsigned)(tiff->ep - tiff->rp))
		fz_throw(ctx, FZ_ERROR_GENERIC, "overlarge IFD entry count %u", count);

	offset += 2;
	for (i = 0; i < count; i++)
	{
		tiff_read_tag(ctx, tiff, offset);
		offset += 12;
	}
}

static void
tiff_ycc_to_rgb(fz_context *ctx, struct tiff *tiff)
{
	unsigned x, y;

	for (y = 0; y < tiff->imagelength; y++)
	{
		unsigned char * row = &tiff->samples[tiff->stride * y];
		for (x = 0; x < tiff->imagewidth; x++)
		{
			int ycc[3];
			ycc[0] = row[x * 3 + 0];
			ycc[1] = row[x * 3 + 1] - 128;
			ycc[2] = row[x * 3 + 2] - 128;

			row[x * 3 + 0] = fz_clampi(ycc[0] + 1.402f * ycc[2], 0, 255);
			row[x * 3 + 1] = fz_clampi(ycc[0] - 0.34413f * ycc[1] - 0.71414f * ycc[2], 0, 255);
			row[x * 3 + 2] = fz_clampi(ycc[0] + 1.772f * ycc[1], 0, 255);
		}
	}
}

static void
tiff_decode_ifd(fz_context *ctx, struct tiff *tiff)
{
	unsigned i;

	if (tiff->imagelength <= 0)
		fz_throw(ctx, FZ_ERROR_GENERIC, "image height must be > 0");
	if (tiff->imagewidth <= 0)
		fz_throw(ctx, FZ_ERROR_GENERIC, "image width must be > 0");

	if (tiff->imagelength > UINT_MAX / tiff->imagewidth / (tiff->samplesperpixel + 2) / (tiff->bitspersample / 8 + 1))
		fz_throw(ctx, FZ_ERROR_GENERIC, "image too large");

	if (tiff->planar != 1)
		fz_throw(ctx, FZ_ERROR_GENERIC, "image data is not in chunky format");

	if (tiff->photometric == 6)
	{
		if (tiff->samplesperpixel != 3)
			fz_throw(ctx, FZ_ERROR_GENERIC, "unsupported samples per pixel when subsampling");
		if (tiff->bitspersample != 8)
			fz_throw(ctx, FZ_ERROR_GENERIC, "unsupported bits per sample when subsampling");
		if (tiff->ycbcrsubsamp[0] == 0 || tiff->ycbcrsubsamp[1] == 0)
			fz_throw(ctx, FZ_ERROR_GENERIC, "unsupported subsampling factor");
	}

	tiff->stride = (tiff->imagewidth * tiff->samplesperpixel * tiff->bitspersample + 7) / 8;
	tiff->tilestride = (tiff->tilewidth * tiff->samplesperpixel * tiff->bitspersample + 7) / 8;

	switch (tiff->photometric)
	{
	case 0: /* WhiteIsZero -- inverted */
		tiff->colorspace = fz_device_gray(ctx);
		break;
	case 1: /* BlackIsZero */
		tiff->colorspace = fz_device_gray(ctx);
		break;
	case 2: /* RGB */
		tiff->colorspace = fz_device_rgb(ctx);
		break;
	case 3: /* RGBPal */
		tiff->colorspace = fz_device_rgb(ctx);
		break;
	case 5: /* CMYK */
		tiff->colorspace = fz_device_cmyk(ctx);
		break;
	case 6: /* YCbCr */
		/* it's probably a jpeg ... we let jpeg convert to rgb */
		tiff->colorspace = fz_device_rgb(ctx);
		break;
	case 8: /* 1976 CIE L*a*b* */
		tiff->colorspace = fz_device_lab(ctx);
		break;
	case 32844: /* SGI CIE Log 2 L (16bpp Greyscale) */
		tiff->colorspace = fz_device_gray(ctx);
		if (tiff->bitspersample != 8)
			tiff->bitspersample = 8;
		tiff->stride >>= 1;
		break;
	case 32845: /* SGI CIE Log 2 L, u, v (24bpp or 32bpp) */
		tiff->colorspace = fz_device_rgb(ctx);
		if (tiff->bitspersample != 8)
			tiff->bitspersample = 8;
		tiff->stride >>= 1;
		break;
	default:
		fz_throw(ctx, FZ_ERROR_GENERIC, "unknown photometric: %d", tiff->photometric);
	}

	switch (tiff->resolutionunit)
	{
	case 2:
		/* no unit conversion needed */
		break;
	case 3:
		tiff->xresolution = tiff->xresolution * 254 / 100;
		tiff->yresolution = tiff->yresolution * 254 / 100;
		break;
	default:
		tiff->xresolution = 96;
		tiff->yresolution = 96;
		break;
	}

	/* Note xres and yres could be 0 even if unit was set. If so default to 96dpi. */
	if (tiff->xresolution == 0 || tiff->yresolution == 0)
	{
		tiff->xresolution = 96;
		tiff->yresolution = 96;
	}

	if (tiff->rowsperstrip > tiff->imagelength)
		tiff->rowsperstrip = tiff->imagelength;

	/* some creators don't write byte counts for uncompressed images */
	if (tiff->compression == 1)
	{
		if (!tiff->tilelength && !tiff->tilewidth && !tiff->stripbytecounts)
		{
			tiff->stripbytecountslen = (tiff->imagelength + tiff->rowsperstrip - 1) / tiff->rowsperstrip;
			tiff->stripbytecounts = fz_malloc_array(ctx, tiff->stripbytecountslen, sizeof(unsigned));
			for (i = 0; i < tiff->stripbytecountslen; i++)
				tiff->stripbytecounts[i] = tiff->rowsperstrip * tiff->stride;
		}
		if (tiff->tilelength && tiff->tilewidth && !tiff->tilebytecounts)
		{
			unsigned tilesdown = (tiff->imagelength + tiff->tilelength - 1) / tiff->tilelength;
			unsigned tilesacross = (tiff->imagewidth + tiff->tilewidth - 1) / tiff->tilewidth;
			tiff->tilebytecountslen = tilesacross * tilesdown;
			tiff->tilebytecounts = fz_malloc_array(ctx, tiff->tilebytecountslen, sizeof(unsigned));
			for (i = 0; i < tiff->tilebytecountslen; i++)
				tiff->tilebytecounts[i] = tiff->tilelength * tiff->tilestride;
		}
	}

	/* some creators write strip tags when they meant to write tile tags... */
	if (tiff->tilelength && tiff->tilewidth)
	{
		if (!tiff->tileoffsets && !tiff->tileoffsetslen &&
				tiff->stripoffsets && tiff->stripoffsetslen)
		{
			tiff->tileoffsets = tiff->stripoffsets;
			tiff->tileoffsetslen = tiff->stripoffsetslen;
			tiff->stripoffsets = NULL;
			tiff->stripoffsetslen = 0;
		}
		if (!tiff->tilebytecounts && !tiff->tilebytecountslen &&
				tiff->stripbytecounts && tiff->stripbytecountslen)
		{
			tiff->tilebytecounts = tiff->stripbytecounts;
			tiff->tilebytecountslen = tiff->stripbytecountslen;
			tiff->stripbytecounts = NULL;
			tiff->stripbytecountslen = 0;
		}
	}
}

static void
tiff_decode_samples(fz_context *ctx, struct tiff *tiff)
{
	unsigned i;

	tiff->samples = fz_malloc_array(ctx, tiff->imagelength, tiff->stride);
	memset(tiff->samples, 0x55, tiff->imagelength * tiff->stride);

	if (tiff->tilelength && tiff->tilewidth && tiff->tileoffsets && tiff->tilebytecounts)
		tiff_decode_tiles(ctx, tiff);
	else if (tiff->rowsperstrip && tiff->stripoffsets && tiff->stripbytecounts)
		tiff_decode_strips(ctx, tiff);
	else
		fz_throw(ctx, FZ_ERROR_GENERIC, "image is missing both strip and tile data");

	/* Predictor (only for LZW and Flate) */
	if ((tiff->compression == 5 || tiff->compression == 8 || tiff->compression == 32946) && tiff->predictor == 2)
	{
		unsigned char *p = tiff->samples;
		for (i = 0; i < tiff->imagelength; i++)
		{
			tiff_unpredict_line(p, tiff->imagewidth, tiff->samplesperpixel, tiff->bitspersample);
			p += tiff->stride;
		}
	}

	/* YCbCr -> RGB, but JPEG already has done this conversion  */
	if (tiff->photometric == 6 && tiff->compression != 6 && tiff->compression != 7)
		tiff_ycc_to_rgb(ctx, tiff);

	/* RGBPal */
	if (tiff->photometric == 3 && tiff->colormap)
		tiff_expand_colormap(ctx, tiff);

	/* WhiteIsZero .. invert */
	if (tiff->photometric == 0)
	{
		unsigned char *p = tiff->samples;
		for (i = 0; i < tiff->imagelength; i++)
		{
			tiff_invert_line(p, tiff->imagewidth, tiff->samplesperpixel, tiff->bitspersample, tiff->extrasamples);
			p += tiff->stride;
		}
	}

	/* Premultiplied transparency */
	if (tiff->extrasamples == 1)
	{
		/* In GhostXPS we undo the premultiplication here; muxps holds
		 * all our images premultiplied by default, so nothing to do.
		 */
	}

	/* Non-premultiplied transparency */
	if (tiff->extrasamples == 2)
	{
		/* Premultiplied files are corrected for elsewhere */
	}

	/* Byte swap 16-bit images to big endian if necessary */
	if (tiff->bitspersample == 16 && tiff->order == TII)
		tiff_swap_byte_order(tiff->samples, tiff->imagewidth * tiff->imagelength * tiff->samplesperpixel);

	/* Lab colorspace expects all sample components 0..255.
	TIFF supplies them as L = 0..255, a/b = -128..127 (for
	8 bits per sample, -32768..32767 for 16 bits per sample)
	Scale them to the colorspace's expectations. */
	if (tiff->photometric == 8 && tiff->samplesperpixel == 3)
		tiff_scale_lab_samples(ctx, tiff->samples, tiff->bitspersample, tiff->imagewidth * tiff->imagelength);
}

fz_pixmap *
fz_load_tiff_subimage(fz_context *ctx, unsigned char *buf, size_t len, int subimage)
{
	fz_pixmap *image = NULL;
	struct tiff tiff = { 0 };
	int alpha;

	fz_var(image);

	fz_try(ctx)
	{
		tiff_read_header(ctx, &tiff, buf, len);
		tiff_seek_ifd(ctx, &tiff, subimage);
		tiff_read_ifd(ctx, &tiff);

		/* Decode the image data */
		tiff_decode_ifd(ctx, &tiff);
		tiff_decode_samples(ctx, &tiff);

		/* Expand into fz_pixmap struct */
		alpha = tiff.extrasamples != 0;
		image = fz_new_pixmap(ctx, tiff.colorspace, tiff.imagewidth, tiff.imagelength, NULL, alpha);
		image->xres = tiff.xresolution;
		image->yres = tiff.yresolution;

		fz_unpack_tile(ctx, image, tiff.samples, tiff.samplesperpixel, tiff.bitspersample, tiff.stride, 0);

		/* We should only do this on non-pre-multiplied images, but files in the wild are bad */
		/* TODO: check if any samples are non-premul to detect bad files */
		if (tiff.extrasamples /* == 2 */)
			fz_premultiply_pixmap(ctx, image);
	}
	fz_always(ctx)
	{
		/* Clean up scratch memory */
		fz_free(ctx, tiff.colormap);
		fz_free(ctx, tiff.stripoffsets);
		fz_free(ctx, tiff.stripbytecounts);
		fz_free(ctx, tiff.tileoffsets);
		fz_free(ctx, tiff.tilebytecounts);
		fz_free(ctx, tiff.data);
		fz_free(ctx, tiff.samples);
		fz_free(ctx, tiff.profile);
	}
	fz_catch(ctx)
	{
		fz_drop_pixmap(ctx, image);
		fz_rethrow(ctx);
	}

	return image;
}

fz_pixmap *
fz_load_tiff(fz_context *ctx, unsigned char *buf, size_t len)
{
	return fz_load_tiff_subimage(ctx, buf, len, 0);
}

void
fz_load_tiff_info_subimage(fz_context *ctx, unsigned char *buf, size_t len, int *wp, int *hp, int *xresp, int *yresp, fz_colorspace **cspacep, int subimage)
{
	struct tiff tiff = { 0 };

	fz_try(ctx)
	{
		tiff_read_header(ctx, &tiff, buf, len);
		tiff_seek_ifd(ctx, &tiff, subimage);
		tiff_read_ifd(ctx, &tiff);

		tiff_decode_ifd(ctx, &tiff);

		*wp = tiff.imagewidth;
		*hp = tiff.imagelength;
		*xresp = (tiff.xresolution ? tiff.xresolution : 96);
		*yresp = (tiff.yresolution ? tiff.yresolution : 96);
		if (tiff.extrasamples /* == 2 */)
			*cspacep = fz_device_rgb(ctx);
		else
			*cspacep = tiff.colorspace;
	}
	fz_always(ctx)
	{
		/* Clean up scratch memory */
		fz_free(ctx, tiff.colormap);
		fz_free(ctx, tiff.stripoffsets);
		fz_free(ctx, tiff.stripbytecounts);
		fz_free(ctx, tiff.samples);
		fz_free(ctx, tiff.profile);
	}
	fz_catch(ctx)
	{
		fz_rethrow(ctx);
	}
}

void
fz_load_tiff_info(fz_context *ctx, unsigned char *buf, size_t len, int *wp, int *hp, int *xresp, int *yresp, fz_colorspace **cspacep)
{
	fz_load_tiff_info_subimage(ctx, buf, len, wp, hp, xresp, yresp, cspacep, 0);
}

int
fz_load_tiff_subimage_count(fz_context *ctx, unsigned char *buf, size_t len)
{
	unsigned offset;
	unsigned subimage_count = 0;
	struct tiff tiff = { 0 };

	tiff_read_header(ctx, &tiff, buf, len);

	offset = tiff.ifd_offset;

	do {
		subimage_count++;
		offset = tiff_next_ifd(ctx, &tiff, offset);
	} while (offset != 0);

	return subimage_count;
}