1 /*
2  * jcmarker.c
3  *
4  * Copyright (C) 1991-1998, Thomas G. Lane.
5  * This file is part of the Independent JPEG Group's software.
6  * For conditions of distribution and use, see the accompanying README file.
7  *
8  * This file contains routines to write JPEG datastream markers.
9  */
10 
11 #define JPEG_INTERNALS
12 #include "jinclude.h"
13 #include "jpeglib.h"
14 
15 
16 typedef enum {			/* JPEG marker codes */
17   M_SOF0  = 0xc0,
18   M_SOF1  = 0xc1,
19   M_SOF2  = 0xc2,
20   M_SOF3  = 0xc3,
21 
22   M_SOF5  = 0xc5,
23   M_SOF6  = 0xc6,
24   M_SOF7  = 0xc7,
25 
26   M_JPG   = 0xc8,
27   M_SOF9  = 0xc9,
28   M_SOF10 = 0xca,
29   M_SOF11 = 0xcb,
30 
31   M_SOF13 = 0xcd,
32   M_SOF14 = 0xce,
33   M_SOF15 = 0xcf,
34 
35   M_DHT   = 0xc4,
36 
37   M_DAC   = 0xcc,
38 
39   M_RST0  = 0xd0,
40   M_RST1  = 0xd1,
41   M_RST2  = 0xd2,
42   M_RST3  = 0xd3,
43   M_RST4  = 0xd4,
44   M_RST5  = 0xd5,
45   M_RST6  = 0xd6,
46   M_RST7  = 0xd7,
47 
48   M_SOI   = 0xd8,
49   M_EOI   = 0xd9,
50   M_SOS   = 0xda,
51   M_DQT   = 0xdb,
52   M_DNL   = 0xdc,
53   M_DRI   = 0xdd,
54   M_DHP   = 0xde,
55   M_EXP   = 0xdf,
56 
57   M_APP0  = 0xe0,
58   M_APP1  = 0xe1,
59   M_APP2  = 0xe2,
60   M_APP3  = 0xe3,
61   M_APP4  = 0xe4,
62   M_APP5  = 0xe5,
63   M_APP6  = 0xe6,
64   M_APP7  = 0xe7,
65   M_APP8  = 0xe8,
66   M_APP9  = 0xe9,
67   M_APP10 = 0xea,
68   M_APP11 = 0xeb,
69   M_APP12 = 0xec,
70   M_APP13 = 0xed,
71   M_APP14 = 0xee,
72   M_APP15 = 0xef,
73 
74   M_JPG0  = 0xf0,
75   M_JPG13 = 0xfd,
76   M_COM   = 0xfe,
77 
78   M_TEM   = 0x01,
79 
80   M_ERROR = 0x100
81 } JPEG_MARKER;
82 
83 
84 /* Private state */
85 
86 typedef struct {
87   struct jpeg_marker_writer pub; /* public fields */
88 
89   unsigned int last_restart_interval; /* last DRI value emitted; 0 after SOI */
90 } my_marker_writer;
91 
92 typedef my_marker_writer * my_marker_ptr;
93 
94 
95 /*
96  * Basic output routines.
97  *
98  * Note that we do not support suspension while writing a marker.
99  * Therefore, an application using suspension must ensure that there is
100  * enough buffer space for the initial markers (typ. 600-700 bytes) before
101  * calling jpeg_start_compress, and enough space to write the trailing EOI
102  * (a few bytes) before calling jpeg_finish_compress.  Multipass compression
103  * modes are not supported at all with suspension, so those two are the only
104  * points where markers will be written.
105  */
106 
107 LOCAL(void)
emit_byte(j_compress_ptr cinfo,int val)108 emit_byte (j_compress_ptr cinfo, int val)
109 /* Emit a byte */
110 {
111   struct jpeg_destination_mgr * dest = cinfo->dest;
112 
113   *(dest->next_output_byte)++ = (JOCTET) val;
114   if (--dest->free_in_buffer == 0) {
115     if (! (*dest->empty_output_buffer) (cinfo))
116       ERREXIT(cinfo, JERR_CANT_SUSPEND);
117   }
118 }
119 
120 
121 LOCAL(void)
emit_marker(j_compress_ptr cinfo,JPEG_MARKER mark)122 emit_marker (j_compress_ptr cinfo, JPEG_MARKER mark)
123 /* Emit a marker code */
124 {
125   emit_byte(cinfo, 0xFF);
126   emit_byte(cinfo, (int) mark);
127 }
128 
129 
130 LOCAL(void)
emit_2bytes(j_compress_ptr cinfo,int value)131 emit_2bytes (j_compress_ptr cinfo, int value)
132 /* Emit a 2-byte integer; these are always MSB first in JPEG files */
133 {
134   emit_byte(cinfo, (value >> 8) & 0xFF);
135   emit_byte(cinfo, value & 0xFF);
136 }
137 
138 
139 /*
140  * Routines to write specific marker types.
141  */
142 
143 LOCAL(int)
emit_dqt(j_compress_ptr cinfo,int index)144 emit_dqt (j_compress_ptr cinfo, int index)
145 /* Emit a DQT marker */
146 /* Returns the precision used (0 = 8bits, 1 = 16bits) for baseline checking */
147 {
148   JQUANT_TBL * qtbl = cinfo->quant_tbl_ptrs[index];
149   int prec;
150   int i;
151 
152   if (qtbl == NULL)
153     ERREXIT1(cinfo, JERR_NO_QUANT_TABLE, index);
154 
155   prec = 0;
156   for (i = 0; i < DCTSIZE2; i++) {
157     if (qtbl->quantval[i] > 255)
158       prec = 1;
159   }
160 
161   if (! qtbl->sent_table) {
162     emit_marker(cinfo, M_DQT);
163 
164     emit_2bytes(cinfo, prec ? DCTSIZE2*2 + 1 + 2 : DCTSIZE2 + 1 + 2);
165 
166     emit_byte(cinfo, index + (prec<<4));
167 
168     for (i = 0; i < DCTSIZE2; i++) {
169       /* The table entries must be emitted in zigzag order. */
170       unsigned int qval = qtbl->quantval[jpeg_natural_order[i]];
171       if (prec)
172 	emit_byte(cinfo, (int) (qval >> 8));
173       emit_byte(cinfo, (int) (qval & 0xFF));
174     }
175 
176     qtbl->sent_table = TRUE;
177   }
178 
179   return prec;
180 }
181 
182 
183 LOCAL(void)
emit_dht(j_compress_ptr cinfo,int index,boolean is_ac)184 emit_dht (j_compress_ptr cinfo, int index, boolean is_ac)
185 /* Emit a DHT marker */
186 {
187   JHUFF_TBL * htbl;
188   int length, i;
189 
190   if (is_ac) {
191     htbl = cinfo->ac_huff_tbl_ptrs[index];
192     index += 0x10;		/* output index has AC bit set */
193   } else {
194     htbl = cinfo->dc_huff_tbl_ptrs[index];
195   }
196 
197   if (htbl == NULL)
198     ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, index);
199 
200   if (! htbl->sent_table) {
201     emit_marker(cinfo, M_DHT);
202 
203     length = 0;
204     for (i = 1; i <= 16; i++)
205       length += htbl->bits[i];
206 
207     emit_2bytes(cinfo, length + 2 + 1 + 16);
208     emit_byte(cinfo, index);
209 
210     for (i = 1; i <= 16; i++)
211       emit_byte(cinfo, htbl->bits[i]);
212 
213     for (i = 0; i < length; i++)
214       emit_byte(cinfo, htbl->huffval[i]);
215 
216     htbl->sent_table = TRUE;
217   }
218 }
219 
220 
221 LOCAL(void)
emit_dac(j_compress_ptr cinfo)222 emit_dac (j_compress_ptr cinfo)
223 /* Emit a DAC marker */
224 /* Since the useful info is so small, we want to emit all the tables in */
225 /* one DAC marker.  Therefore this routine does its own scan of the table. */
226 {
227 #ifdef C_ARITH_CODING_SUPPORTED
228   char dc_in_use[NUM_ARITH_TBLS];
229   char ac_in_use[NUM_ARITH_TBLS];
230   int length, i;
231   jpeg_component_info *compptr;
232 
233   for (i = 0; i < NUM_ARITH_TBLS; i++)
234     dc_in_use[i] = ac_in_use[i] = 0;
235 
236   for (i = 0; i < cinfo->comps_in_scan; i++) {
237     compptr = cinfo->cur_comp_info[i];
238     dc_in_use[compptr->dc_tbl_no] = 1;
239     ac_in_use[compptr->ac_tbl_no] = 1;
240   }
241 
242   length = 0;
243   for (i = 0; i < NUM_ARITH_TBLS; i++)
244     length += dc_in_use[i] + ac_in_use[i];
245 
246   emit_marker(cinfo, M_DAC);
247 
248   emit_2bytes(cinfo, length*2 + 2);
249 
250   for (i = 0; i < NUM_ARITH_TBLS; i++) {
251     if (dc_in_use[i]) {
252       emit_byte(cinfo, i);
253       emit_byte(cinfo, cinfo->arith_dc_L[i] + (cinfo->arith_dc_U[i]<<4));
254     }
255     if (ac_in_use[i]) {
256       emit_byte(cinfo, i + 0x10);
257       emit_byte(cinfo, cinfo->arith_ac_K[i]);
258     }
259   }
260 #endif /* C_ARITH_CODING_SUPPORTED */
261 }
262 
263 
264 LOCAL(void)
emit_dri(j_compress_ptr cinfo)265 emit_dri (j_compress_ptr cinfo)
266 /* Emit a DRI marker */
267 {
268   emit_marker(cinfo, M_DRI);
269 
270   emit_2bytes(cinfo, 4);	/* fixed length */
271 
272   emit_2bytes(cinfo, (int) cinfo->restart_interval);
273 }
274 
275 
276 LOCAL(void)
emit_sof(j_compress_ptr cinfo,JPEG_MARKER code)277 emit_sof (j_compress_ptr cinfo, JPEG_MARKER code)
278 /* Emit a SOF marker */
279 {
280   int ci;
281   jpeg_component_info *compptr;
282 
283   emit_marker(cinfo, code);
284 
285   emit_2bytes(cinfo, 3 * cinfo->num_components + 2 + 5 + 1); /* length */
286 
287   /* Make sure image isn't bigger than SOF field can handle */
288   if ((long) cinfo->image_height > 65535L ||
289       (long) cinfo->image_width > 65535L)
290     ERREXIT1(cinfo, JERR_IMAGE_TOO_BIG, (unsigned int) 65535);
291 
292   emit_byte(cinfo, cinfo->data_precision);
293   emit_2bytes(cinfo, (int) cinfo->image_height);
294   emit_2bytes(cinfo, (int) cinfo->image_width);
295 
296   emit_byte(cinfo, cinfo->num_components);
297 
298   for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
299        ci++, compptr++) {
300     emit_byte(cinfo, compptr->component_id);
301     emit_byte(cinfo, (compptr->h_samp_factor << 4) + compptr->v_samp_factor);
302     emit_byte(cinfo, compptr->quant_tbl_no);
303   }
304 }
305 
306 
307 LOCAL(void)
emit_sos(j_compress_ptr cinfo)308 emit_sos (j_compress_ptr cinfo)
309 /* Emit a SOS marker */
310 {
311   int i, td, ta;
312   jpeg_component_info *compptr;
313 
314   emit_marker(cinfo, M_SOS);
315 
316   emit_2bytes(cinfo, 2 * cinfo->comps_in_scan + 2 + 1 + 3); /* length */
317 
318   emit_byte(cinfo, cinfo->comps_in_scan);
319 
320   for (i = 0; i < cinfo->comps_in_scan; i++) {
321     compptr = cinfo->cur_comp_info[i];
322     emit_byte(cinfo, compptr->component_id);
323     td = compptr->dc_tbl_no;
324     ta = compptr->ac_tbl_no;
325     if (cinfo->progressive_mode) {
326       /* Progressive mode: only DC or only AC tables are used in one scan;
327        * furthermore, Huffman coding of DC refinement uses no table at all.
328        * We emit 0 for unused field(s); this is recommended by the P&M text
329        * but does not seem to be specified in the standard.
330        */
331       if (cinfo->Ss == 0) {
332 	ta = 0;			/* DC scan */
333 	if (cinfo->Ah != 0 && !cinfo->arith_code)
334 	  td = 0;		/* no DC table either */
335       } else {
336 	td = 0;			/* AC scan */
337       }
338     }
339     emit_byte(cinfo, (td << 4) + ta);
340   }
341 
342   emit_byte(cinfo, cinfo->Ss);
343   emit_byte(cinfo, cinfo->Se);
344   emit_byte(cinfo, (cinfo->Ah << 4) + cinfo->Al);
345 }
346 
347 
348 LOCAL(void)
emit_jfif_app0(j_compress_ptr cinfo)349 emit_jfif_app0 (j_compress_ptr cinfo)
350 /* Emit a JFIF-compliant APP0 marker */
351 {
352   /*
353    * Length of APP0 block	(2 bytes)
354    * Block ID			(4 bytes - ASCII "JFIF")
355    * Zero byte			(1 byte to terminate the ID string)
356    * Version Major, Minor	(2 bytes - major first)
357    * Units			(1 byte - 0x00 = none, 0x01 = inch, 0x02 = cm)
358    * Xdpu			(2 bytes - dots per unit horizontal)
359    * Ydpu			(2 bytes - dots per unit vertical)
360    * Thumbnail X size		(1 byte)
361    * Thumbnail Y size		(1 byte)
362    */
363 
364   emit_marker(cinfo, M_APP0);
365 
366   emit_2bytes(cinfo, 2 + 4 + 1 + 2 + 1 + 2 + 2 + 1 + 1); /* length */
367 
368   emit_byte(cinfo, 0x4A);	/* Identifier: ASCII "JFIF" */
369   emit_byte(cinfo, 0x46);
370   emit_byte(cinfo, 0x49);
371   emit_byte(cinfo, 0x46);
372   emit_byte(cinfo, 0);
373   emit_byte(cinfo, cinfo->JFIF_major_version); /* Version fields */
374   emit_byte(cinfo, cinfo->JFIF_minor_version);
375   emit_byte(cinfo, cinfo->density_unit); /* Pixel size information */
376   emit_2bytes(cinfo, (int) cinfo->X_density);
377   emit_2bytes(cinfo, (int) cinfo->Y_density);
378   emit_byte(cinfo, 0);		/* No thumbnail image */
379   emit_byte(cinfo, 0);
380 }
381 
382 
383 LOCAL(void)
emit_adobe_app14(j_compress_ptr cinfo)384 emit_adobe_app14 (j_compress_ptr cinfo)
385 /* Emit an Adobe APP14 marker */
386 {
387   /*
388    * Length of APP14 block	(2 bytes)
389    * Block ID			(5 bytes - ASCII "Adobe")
390    * Version Number		(2 bytes - currently 100)
391    * Flags0			(2 bytes - currently 0)
392    * Flags1			(2 bytes - currently 0)
393    * Color transform		(1 byte)
394    *
395    * Although Adobe TN 5116 mentions Version = 101, all the Adobe files
396    * now in circulation seem to use Version = 100, so that's what we write.
397    *
398    * We write the color transform byte as 1 if the JPEG color space is
399    * YCbCr, 2 if it's YCCK, 0 otherwise.  Adobe's definition has to do with
400    * whether the encoder performed a transformation, which is pretty useless.
401    */
402 
403   emit_marker(cinfo, M_APP14);
404 
405   emit_2bytes(cinfo, 2 + 5 + 2 + 2 + 2 + 1); /* length */
406 
407   emit_byte(cinfo, 0x41);	/* Identifier: ASCII "Adobe" */
408   emit_byte(cinfo, 0x64);
409   emit_byte(cinfo, 0x6F);
410   emit_byte(cinfo, 0x62);
411   emit_byte(cinfo, 0x65);
412   emit_2bytes(cinfo, 100);	/* Version */
413   emit_2bytes(cinfo, 0);	/* Flags0 */
414   emit_2bytes(cinfo, 0);	/* Flags1 */
415   switch (cinfo->jpeg_color_space) {
416   case JCS_YCbCr:
417     emit_byte(cinfo, 1);	/* Color transform = 1 */
418     break;
419   case JCS_YCCK:
420     emit_byte(cinfo, 2);	/* Color transform = 2 */
421     break;
422   default:
423     emit_byte(cinfo, 0);	/* Color transform = 0 */
424     break;
425   }
426 }
427 
428 
429 /*
430  * These routines allow writing an arbitrary marker with parameters.
431  * The only intended use is to emit COM or APPn markers after calling
432  * write_file_header and before calling write_frame_header.
433  * Other uses are not guaranteed to produce desirable results.
434  * Counting the parameter bytes properly is the caller's responsibility.
435  */
436 
437 METHODDEF(void)
write_marker_header(j_compress_ptr cinfo,int marker,unsigned int datalen)438 write_marker_header (j_compress_ptr cinfo, int marker, unsigned int datalen)
439 /* Emit an arbitrary marker header */
440 {
441   if (datalen > (unsigned int) 65533)		/* safety check */
442     ERREXIT(cinfo, JERR_BAD_LENGTH);
443 
444   emit_marker(cinfo, (JPEG_MARKER) marker);
445 
446   emit_2bytes(cinfo, (int) (datalen + 2));	/* total length */
447 }
448 
449 METHODDEF(void)
write_marker_byte(j_compress_ptr cinfo,int val)450 write_marker_byte (j_compress_ptr cinfo, int val)
451 /* Emit one byte of marker parameters following write_marker_header */
452 {
453   emit_byte(cinfo, val);
454 }
455 
456 
457 /*
458  * Write datastream header.
459  * This consists of an SOI and optional APPn markers.
460  * We recommend use of the JFIF marker, but not the Adobe marker,
461  * when using YCbCr or grayscale data.  The JFIF marker should NOT
462  * be used for any other JPEG colorspace.  The Adobe marker is helpful
463  * to distinguish RGB, CMYK, and YCCK colorspaces.
464  * Note that an application can write additional header markers after
465  * jpeg_start_compress returns.
466  */
467 
468 METHODDEF(void)
write_file_header(j_compress_ptr cinfo)469 write_file_header (j_compress_ptr cinfo)
470 {
471   my_marker_ptr marker = (my_marker_ptr) cinfo->marker;
472 
473   emit_marker(cinfo, M_SOI);	/* first the SOI */
474 
475   /* SOI is defined to reset restart interval to 0 */
476   marker->last_restart_interval = 0;
477 
478   if (cinfo->write_JFIF_header)	/* next an optional JFIF APP0 */
479     emit_jfif_app0(cinfo);
480   if (cinfo->write_Adobe_marker) /* next an optional Adobe APP14 */
481     emit_adobe_app14(cinfo);
482 }
483 
484 
485 /*
486  * Write frame header.
487  * This consists of DQT and SOFn markers.
488  * Note that we do not emit the SOF until we have emitted the DQT(s).
489  * This avoids compatibility problems with incorrect implementations that
490  * try to error-check the quant table numbers as soon as they see the SOF.
491  */
492 
493 METHODDEF(void)
write_frame_header(j_compress_ptr cinfo)494 write_frame_header (j_compress_ptr cinfo)
495 {
496   int ci, prec;
497   boolean is_baseline;
498   jpeg_component_info *compptr;
499 
500   /* Emit DQT for each quantization table.
501    * Note that emit_dqt() suppresses any duplicate tables.
502    */
503   prec = 0;
504   for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
505        ci++, compptr++) {
506     prec += emit_dqt(cinfo, compptr->quant_tbl_no);
507   }
508   /* now prec is nonzero iff there are any 16-bit quant tables. */
509 
510   /* Check for a non-baseline specification.
511    * Note we assume that Huffman table numbers won't be changed later.
512    */
513   if (cinfo->arith_code || cinfo->progressive_mode ||
514       cinfo->data_precision != 8) {
515     is_baseline = FALSE;
516   } else {
517     is_baseline = TRUE;
518     for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
519 	 ci++, compptr++) {
520       if (compptr->dc_tbl_no > 1 || compptr->ac_tbl_no > 1)
521 	is_baseline = FALSE;
522     }
523     if (prec && is_baseline) {
524       is_baseline = FALSE;
525       /* If it's baseline except for quantizer size, warn the user */
526       TRACEMS(cinfo, 0, JTRC_16BIT_TABLES);
527     }
528   }
529 
530   /* Emit the proper SOF marker */
531   if (cinfo->arith_code) {
532     emit_sof(cinfo, M_SOF9);	/* SOF code for arithmetic coding */
533   } else {
534     if (cinfo->progressive_mode)
535       emit_sof(cinfo, M_SOF2);	/* SOF code for progressive Huffman */
536     else if (is_baseline)
537       emit_sof(cinfo, M_SOF0);	/* SOF code for baseline implementation */
538     else
539       emit_sof(cinfo, M_SOF1);	/* SOF code for non-baseline Huffman file */
540   }
541 }
542 
543 
544 /*
545  * Write scan header.
546  * This consists of DHT or DAC markers, optional DRI, and SOS.
547  * Compressed data will be written following the SOS.
548  */
549 
550 METHODDEF(void)
write_scan_header(j_compress_ptr cinfo)551 write_scan_header (j_compress_ptr cinfo)
552 {
553   my_marker_ptr marker = (my_marker_ptr) cinfo->marker;
554   int i;
555   jpeg_component_info *compptr;
556 
557   if (cinfo->arith_code) {
558     /* Emit arith conditioning info.  We may have some duplication
559      * if the file has multiple scans, but it's so small it's hardly
560      * worth worrying about.
561      */
562     emit_dac(cinfo);
563   } else {
564     /* Emit Huffman tables.
565      * Note that emit_dht() suppresses any duplicate tables.
566      */
567     for (i = 0; i < cinfo->comps_in_scan; i++) {
568       compptr = cinfo->cur_comp_info[i];
569       if (cinfo->progressive_mode) {
570 	/* Progressive mode: only DC or only AC tables are used in one scan */
571 	if (cinfo->Ss == 0) {
572 	  if (cinfo->Ah == 0)	/* DC needs no table for refinement scan */
573 	    emit_dht(cinfo, compptr->dc_tbl_no, FALSE);
574 	} else {
575 	  emit_dht(cinfo, compptr->ac_tbl_no, TRUE);
576 	}
577       } else {
578 	/* Sequential mode: need both DC and AC tables */
579 	emit_dht(cinfo, compptr->dc_tbl_no, FALSE);
580 	emit_dht(cinfo, compptr->ac_tbl_no, TRUE);
581       }
582     }
583   }
584 
585   /* Emit DRI if required --- note that DRI value could change for each scan.
586    * We avoid wasting space with unnecessary DRIs, however.
587    */
588   if (cinfo->restart_interval != marker->last_restart_interval) {
589     emit_dri(cinfo);
590     marker->last_restart_interval = cinfo->restart_interval;
591   }
592 
593   emit_sos(cinfo);
594 }
595 
596 
597 /*
598  * Write datastream trailer.
599  */
600 
601 METHODDEF(void)
write_file_trailer(j_compress_ptr cinfo)602 write_file_trailer (j_compress_ptr cinfo)
603 {
604   emit_marker(cinfo, M_EOI);
605 }
606 
607 
608 /*
609  * Write an abbreviated table-specification datastream.
610  * This consists of SOI, DQT and DHT tables, and EOI.
611  * Any table that is defined and not marked sent_table = TRUE will be
612  * emitted.  Note that all tables will be marked sent_table = TRUE at exit.
613  */
614 
615 METHODDEF(void)
write_tables_only(j_compress_ptr cinfo)616 write_tables_only (j_compress_ptr cinfo)
617 {
618   int i;
619 
620   emit_marker(cinfo, M_SOI);
621 
622   for (i = 0; i < NUM_QUANT_TBLS; i++) {
623     if (cinfo->quant_tbl_ptrs[i] != NULL)
624       (void) emit_dqt(cinfo, i);
625   }
626 
627   if (! cinfo->arith_code) {
628     for (i = 0; i < NUM_HUFF_TBLS; i++) {
629       if (cinfo->dc_huff_tbl_ptrs[i] != NULL)
630 	emit_dht(cinfo, i, FALSE);
631       if (cinfo->ac_huff_tbl_ptrs[i] != NULL)
632 	emit_dht(cinfo, i, TRUE);
633     }
634   }
635 
636   emit_marker(cinfo, M_EOI);
637 }
638 
639 
640 /*
641  * Initialize the marker writer module.
642  */
643 
644 GLOBAL(void)
jinit_marker_writer(j_compress_ptr cinfo)645 jinit_marker_writer (j_compress_ptr cinfo)
646 {
647   my_marker_ptr marker;
648 
649   /* Create the subobject */
650   marker = (my_marker_ptr)
651     (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
652 				SIZEOF(my_marker_writer));
653   cinfo->marker = (struct jpeg_marker_writer *) marker;
654   /* Initialize method pointers */
655   marker->pub.write_file_header = write_file_header;
656   marker->pub.write_frame_header = write_frame_header;
657   marker->pub.write_scan_header = write_scan_header;
658   marker->pub.write_file_trailer = write_file_trailer;
659   marker->pub.write_tables_only = write_tables_only;
660   marker->pub.write_marker_header = write_marker_header;
661   marker->pub.write_marker_byte = write_marker_byte;
662   /* Initialize private state */
663   marker->last_restart_interval = 0;
664 }
665