-
Notifications
You must be signed in to change notification settings - Fork 0
/
Copy pathdecompressor_broken.cpp
540 lines (505 loc) · 23.4 KB
/
decompressor_broken.cpp
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
/*******************************************************************************
Start here:
Introduction
------------
JPEG uses a lossy compression scheme that looks loosely like this:
1. Divide image into blocks (8x8 pixels in this case)
2. Apply a discrete cosine transform on each block. This will transform the
block into a frequency-domain representation, We have still not done any
compression.
3. Reshuffle the coefficients according to a zig-zag pattern. This will merely
move all low-frequency components together.
4. Quantize the coefficents. This means scale down the coefficients and round
them to integers. This is where we lose information, alas, lossy compression.
The idea is that frequency components with low amplitude can be removed
without destroying the visual impression of the picture.
5. Come up with an efficient system of storing the coefficients, and keep in
mind that many may be zeros.
Suggested reading on wikipedia and other sources: DCT, JPEG (especially
sections Block splitting, Discrete cosine transform, Quantization, Entropy
coding.
Again, the actual compression is done in step 4. This is also where the
compressor has to make good decisions. Quantify much, and we will lose a lot
of information, or quantify only a little, and the compressed image becomes
(too) large. For the decompressor, life is easier though. All that the
decompressor needs to do is to read the level of quantization per block and
scale up the matrix.
An implementation of "VPEG"
---------------------------
Below is an attempt to decompress an gray-scale image, that is, each pixel
has a single value 0-255.
Instead of JPEG (but with inspiration it), we use a very simple coding schema
with seven different patterns. The DC coefficient ([0][0] in the matrix) is
stored separately from the other coefficients. The other coefficients are then
stored in a run-length encoding schema, where consecutive zeros are represented
with a single number.
Below are the seven different patterns. (We use the non-standard notation 0b
to denote a binary value. E.g., 0b01011010 is the same as 0x5a which is the
same as 90.)
0b101000yy 0bxxxxxxxx 0bxxxxxxxxx: start of block, quantifization value is yy,
DC value is xxxxxxxxxxxxxxxx (big-endian)
0b0sxxxxxx: coefficient value sxxxxxx (1-complement sign
s=0 means 1, s=1 means -1)
0b100zzzzs 0bxxxxxxxx: zzzzz zeros, followed by coefficient value
sxxxxxxxx
0b10101100: end of block
0b10101110: next row of blocks
0b10101111: end of file
0b11111111 0bxxxxxxxx: ignore next xxxxxxxx bytes
The reader should again note that this schema is not at all the same as the
Huffman encoding in the JPEG format. Only the ideas and algorithms are the same.
Problem
-------
However, there are some bugs in the decompression code below :(
One tiny function is even missing!
To participate in the drawing of great prices, write down the information
(a timestamp and a symbol) found in the image together with your name and
e-mail and give it to the people in the Vizrt/Ardendo booth at Uniaden. Also, be
at the booth on Tuesday at the given time to participate in the drawing.
Even if you do not solve the puzzle, we still want to talk to you. We do not
only search people who eats bits and bytes for breakfast, but all kind of
talented persons!
Hints
-----
- Read the compiler warnings/errors.
- Read each line carefully.
- Make sure you and your debugger are a team.
- There are no known bugs in the data, quant_values, or zigzag_order constants.
*******************************************************************************/
#include <stdio.h>
#include <math.h>
#include <string.h>
#include <assert.h>
unsigned char data[] =
{
0xa0, 0x07, 0xf8, 0x9e, 0x00, 0x9e, 0x00, 0x9e,
0x00, 0xac, 0xa3, 0x01, 0xe0, 0x11, 0x1c, 0x02,
0x50, 0x58, 0x4b, 0x42, 0x0e, 0x12, 0x07, 0x0a,
0x02, 0x4a, 0x4c, 0x41, 0x46, 0x48, 0x42, 0x06,
0x03, 0x82, 0x01, 0x05, 0x06, 0x02, 0x41, 0x41,
0x87, 0x03, 0x44, 0x8c, 0x01, 0x01, 0x9e, 0x00,
0xac, 0xa2, 0x03, 0xfb, 0x9e, 0x00, 0x9e, 0x00,
0x9e, 0x00, 0xac, 0xa3, 0x01, 0xb9, 0x0c, 0x80,
0x40, 0x05, 0x4b, 0x76, 0x06, 0x45, 0x09, 0x27,
0x02, 0x46, 0x04, 0x45, 0x58, 0x41, 0x42, 0x04,
0x42, 0x02, 0x06, 0x82, 0x01, 0x01, 0x42, 0x01,
0x83, 0x02, 0x87, 0x01, 0x9e, 0x00, 0x9e, 0x00,
0xac, 0xa3, 0x01, 0xee, 0x4e, 0x0e, 0x4b, 0x0d,
0x4c, 0x47, 0x0a, 0x4b, 0x09, 0x44, 0x07, 0x49,
0x08, 0x46, 0x82, 0x04, 0x45, 0x06, 0x45, 0x01,
0x85, 0x03, 0x04, 0x44, 0x01, 0x88, 0x01, 0x42,
0x01, 0x9e, 0x00, 0xac, 0xa0, 0x07, 0xf8, 0x9e,
0x00, 0x9e, 0x00, 0x9e, 0x00, 0xac, 0xff, 0x0e,
0x49, 0x73, 0x61, 0x6b, 0x20, 0x77, 0x61, 0x73,
0x20, 0x68, 0x65, 0x72, 0x65, 0x2e, 0xa0, 0x07,
0xf8, 0x9e, 0x00, 0x9e, 0x00, 0x9e, 0x00, 0xac,
0xa3, 0x01, 0xfa, 0x03, 0x03, 0x41, 0x43, 0x43,
0x82, 0x01, 0x02, 0x03, 0x85, 0x01, 0x42, 0x42,
0x86, 0x01, 0x02, 0x01, 0x89, 0x01, 0x9e, 0x00,
0x9e, 0x00, 0xac, 0xa3, 0x01, 0xf8, 0x44, 0x05,
0x42, 0x04, 0x45, 0x82, 0x02, 0x44, 0x04, 0x85,
0x02, 0x03, 0x43, 0x86, 0x02, 0x43, 0x01, 0x89,
0x02, 0x01, 0x41, 0x9e, 0x00, 0x9e, 0x00, 0xac,
0xae, 0xa3, 0x01, 0xc0, 0x2f, 0x2a, 0x52, 0x5e,
0x49, 0x43, 0x06, 0x03, 0x44, 0x07, 0x09, 0x09,
0x06, 0x05, 0x41, 0x4b, 0x4f, 0x49, 0x44, 0x41,
0x82, 0x02, 0x0c, 0x09, 0x03, 0x01, 0x87, 0x02,
0x44, 0x8f, 0x01, 0x8a, 0x01, 0x01, 0x87, 0x01,
0xac, 0xa3, 0x01, 0x1f, 0x32, 0x77, 0x63, 0x48,
0x0f, 0x07, 0x2b, 0x18, 0x03, 0x12, 0x47, 0x24,
0x0b, 0x44, 0x49, 0x0e, 0x03, 0x41, 0x41, 0x03,
0x05, 0x43, 0x48, 0x4c, 0x4f, 0x82, 0x03, 0x44,
0x82, 0x01, 0x4a, 0x49, 0x42, 0x01, 0x83, 0x01,
0x41, 0x83, 0x02, 0x41, 0x82, 0x01, 0x84, 0x02,
0x83, 0x01, 0x84, 0x01, 0x86, 0x01, 0xac, 0xa3,
0x01, 0xb8, 0x2a, 0x4c, 0x70, 0x17, 0x14, 0x0d,
0x49, 0x50, 0x04, 0x4f, 0x0f, 0x0a, 0x46, 0x41,
0x42, 0x42, 0x42, 0x03, 0x41, 0x02, 0x82, 0x03,
0x41, 0x43, 0x83, 0x01, 0x01, 0x42, 0x82, 0x02,
0x83, 0x01, 0x01, 0x87, 0x01, 0x86, 0x01, 0x9e,
0x00, 0xac, 0xa3, 0x01, 0xad, 0x55, 0x7c, 0x51,
0x55, 0x71, 0x45, 0x43, 0x42, 0x5b, 0x4d, 0x45,
0x83, 0x04, 0x56, 0x83, 0x04, 0x05, 0x08, 0x03,
0x44, 0x42, 0x84, 0x01, 0x02, 0x83, 0x02, 0x84,
0x02, 0x03, 0x03, 0x02, 0x02, 0x86, 0x01, 0x8a,
0x01, 0x82, 0x01, 0x9e, 0x00, 0xac, 0xa3, 0x01,
0x60, 0x81, 0x5e, 0x0c, 0x62, 0x47, 0x02, 0x28,
0x45, 0x49, 0x42, 0x20, 0x52, 0x51, 0x0d, 0x03,
0x0a, 0x43, 0x56, 0x01, 0x46, 0x43, 0x85, 0x07,
0x0a, 0x03, 0x41, 0x84, 0x02, 0x83, 0x03, 0x44,
0x01, 0x02, 0x02, 0x82, 0x02, 0x84, 0x02, 0x41,
0x85, 0x02, 0x41, 0x8d, 0x01, 0x41, 0xac, 0xa3,
0x01, 0x71, 0x19, 0x21, 0x30, 0x06, 0x0e, 0x81,
0x4f, 0x44, 0x01, 0x45, 0x43, 0x0f, 0x44, 0x51,
0x10, 0x08, 0x09, 0x07, 0x4a, 0x05, 0x02, 0x45,
0x82, 0x04, 0x82, 0x01, 0x41, 0x87, 0x01, 0x49,
0x08, 0x41, 0x41, 0x02, 0x85, 0x01, 0x02, 0x01,
0x41, 0x89, 0x01, 0x9e, 0x00, 0xac, 0xa3, 0x01,
0x95, 0x4e, 0x0b, 0x80, 0x54, 0x05, 0x0c, 0x1e,
0x48, 0x01, 0x0b, 0x69, 0x4c, 0x4a, 0x82, 0x07,
0x4b, 0x03, 0x43, 0x49, 0x82, 0x02, 0x05, 0x04,
0x05, 0x83, 0x05, 0x84, 0x05, 0x82, 0x01, 0x04,
0x83, 0x01, 0x85, 0x02, 0x84, 0x03, 0x9e, 0x00,
0xac, 0xa3, 0x01, 0x54, 0x42, 0x5b, 0x30, 0x2b,
0x48, 0x35, 0x49, 0x1c, 0x12, 0x0d, 0x56, 0x4b,
0x04, 0x10, 0x46, 0x49, 0x4f, 0x4d, 0x47, 0x07,
0x45, 0x02, 0x44, 0x44, 0x46, 0x45, 0x02, 0x42,
0x02, 0x02, 0x02, 0x03, 0x41, 0x42, 0x01, 0x82,
0x01, 0x01, 0x03, 0x03, 0x83, 0x01, 0x86, 0x01,
0x02, 0x8a, 0x01, 0xac, 0xff, 0x5e, 0x43, 0x6f,
0x6e, 0x67, 0x72, 0x61, 0x74, 0x75, 0x6c, 0x61,
0x74, 0x69, 0x6f, 0x6e, 0x73, 0x20, 0x66, 0x72,
0x6f, 0x6d, 0x20, 0x56, 0x69, 0x7a, 0x72, 0x74,
0x21, 0x20, 0x46, 0x6f, 0x72, 0x20, 0x74, 0x68,
0x65, 0x20, 0x63, 0x68, 0x61, 0x6e, 0x63, 0x65,
0x20, 0x74, 0x6f, 0x20, 0x61, 0x6e, 0x20, 0x65,
0x78, 0x74, 0x72, 0x61, 0x20, 0x70, 0x72, 0x69,
0x7a, 0x65, 0x2c, 0x20, 0x61, 0x6c, 0x73, 0x6f,
0x20, 0x62, 0x72, 0x69, 0x6e, 0x67, 0x20, 0x74,
0x68, 0x65, 0x20, 0x63, 0x6f, 0x64, 0x65, 0x3a,
0x20, 0x65, 0x61, 0x73, 0x74, 0x65, 0x72, 0x65,
0x67, 0x67, 0x2e, 0x20, 0xa3, 0x01, 0x64, 0x81,
0x44, 0x4d, 0x36, 0x57, 0x48, 0x36, 0x5e, 0x4f,
0x0c, 0x49, 0x48, 0x53, 0x05, 0x04, 0x4a, 0x0c,
0x47, 0x47, 0x01, 0x04, 0x01, 0x04, 0x07, 0x4c,
0x42, 0x03, 0x01, 0x03, 0x82, 0x03, 0x46, 0x41,
0x01, 0x82, 0x01, 0x41, 0x84, 0x02, 0x88, 0x01,
0x01, 0x41, 0x9e, 0x00, 0xac, 0xae, 0xa3, 0x01,
0xf9, 0x02, 0x44, 0x82, 0x02, 0x44, 0x42, 0x82,
0x02, 0x43, 0x02, 0x42, 0x82, 0x02, 0x43, 0x82,
0x02, 0x42, 0x82, 0x02, 0x41, 0x84, 0x02, 0x42,
0x8c, 0x01, 0x41, 0x8c, 0x01, 0x9e, 0x00, 0xac,
0xa3, 0x01, 0x95, 0x80, 0x5d, 0x02, 0x81, 0x40,
0x41, 0x82, 0x20, 0x41, 0x85, 0x06, 0x03, 0x87,
0x02, 0x44, 0x41, 0x86, 0x03, 0x01, 0x01, 0x89,
0x02, 0x9e, 0x00, 0x8e, 0x01, 0xac, 0xa2, 0x03,
0xd6, 0x65, 0x42, 0x62, 0x42, 0x83, 0x1f, 0x42,
0x85, 0x1a, 0x42, 0x87, 0x0a, 0x41, 0x89, 0x07,
0x8d, 0x03, 0x9e, 0x00, 0x9e, 0x00, 0xac, 0xa3,
0x01, 0xb7, 0x2a, 0x76, 0x42, 0x21, 0x54, 0x43,
0x43, 0x0d, 0x0a, 0x45, 0x42, 0x44, 0x43, 0x15,
0x02, 0x43, 0x83, 0x04, 0x4a, 0x08, 0x82, 0x01,
0x82, 0x03, 0x44, 0x43, 0x03, 0x86, 0x01, 0x04,
0x42, 0x41, 0x87, 0x01, 0x01, 0x01, 0x41, 0x8a,
0x01, 0x9e, 0x00, 0xac, 0xa3, 0x01, 0x5f, 0x81,
0x41, 0x52, 0x22, 0x64, 0x0c, 0x27, 0x66, 0x47,
0x0e, 0x5b, 0x4d, 0x4c, 0x0f, 0x07, 0x49, 0x11,
0x4d, 0x42, 0x07, 0x82, 0x01, 0x04, 0x07, 0x82,
0x02, 0x41, 0x41, 0x05, 0x41, 0x01, 0x43, 0x89,
0x02, 0x01, 0x01, 0x41, 0x41, 0x9e, 0x00, 0xac,
0xa3, 0x01, 0x86, 0x0b, 0x6d, 0x4c, 0x2b, 0x09,
0x5d, 0x10, 0x19, 0x43, 0x83, 0x0d, 0x14, 0x5e,
0x0f, 0x05, 0x83, 0x01, 0x46, 0x4e, 0x05, 0x01,
0x02, 0x01, 0x45, 0x01, 0x01, 0x43, 0x86, 0x02,
0x41, 0x03, 0x83, 0x02, 0x41, 0x41, 0x01, 0x91,
0x01, 0x82, 0x01, 0xac, 0xa3, 0x01, 0x20, 0x63,
0x81, 0x42, 0x80, 0x4e, 0x44, 0x45, 0x1b, 0x42,
0x82, 0x24, 0x49, 0x56, 0x82, 0x01, 0x22, 0x4c,
0x0e, 0x41, 0x03, 0x01, 0x07, 0x02, 0x02, 0x01,
0x09, 0x04, 0x84, 0x03, 0x01, 0x01, 0x45, 0x09,
0x01, 0x85, 0x01, 0x85, 0x06, 0x01, 0x8b, 0x01,
0x84, 0x01, 0xac, 0xa3, 0x01, 0x28, 0x66, 0x81,
0x41, 0x17, 0x2f, 0x4c, 0x20, 0x28, 0x15, 0x0b,
0x1a, 0x09, 0x42, 0x44, 0x0c, 0x06, 0x48, 0x49,
0x4a, 0x50, 0x04, 0x03, 0x47, 0x44, 0x01, 0x41,
0x45, 0x85, 0x04, 0x41, 0x04, 0x07, 0x02, 0x42,
0x83, 0x02, 0x84, 0x02, 0x01, 0x02, 0x9e, 0x00,
0xac, 0xa3, 0x01, 0x5e, 0x7f, 0x60, 0x80, 0x44,
0x5f, 0x4e, 0x35, 0x52, 0x4a, 0x83, 0x16, 0x04,
0x45, 0x82, 0x05, 0x4d, 0x0c, 0x44, 0x01, 0x08,
0x02, 0x02, 0x02, 0x82, 0x02, 0x08, 0x03, 0x82,
0x05, 0x82, 0x01, 0x84, 0x04, 0x01, 0x84, 0x01,
0x83, 0x02, 0x01, 0x02, 0x89, 0x01, 0x01, 0x01,
0xac, 0xae, 0xa0, 0x07, 0xf8, 0x9e, 0x00, 0x9e,
0x00, 0x9e, 0x00, 0xac, 0xa3, 0x01, 0x82, 0x80,
0x60, 0x83, 0x23, 0x06, 0x41, 0x50, 0x53, 0x84,
0x21, 0x15, 0x02, 0x41, 0x02, 0x4c, 0x4b, 0x41,
0x03, 0x41, 0x01, 0x05, 0x83, 0x01, 0x43, 0x41,
0x41, 0x83, 0x01, 0x01, 0x02, 0x02, 0x01, 0x87,
0x01, 0x41, 0x8f, 0x01, 0x88, 0x01, 0xac, 0xa3,
0x01, 0xc6, 0x1d, 0x18, 0x51, 0x5c, 0x04, 0x4c,
0x05, 0x42, 0x56, 0x02, 0x44, 0x48, 0x0f, 0x10,
0x41, 0x44, 0x0a, 0x02, 0x4a, 0x83, 0x03, 0x42,
0x49, 0x4a, 0x04, 0x01, 0x42, 0x84, 0x01, 0x0a,
0x02, 0x42, 0x01, 0x01, 0x41, 0x83, 0x01, 0x41,
0x02, 0x01, 0x89, 0x01, 0x42, 0x88, 0x02, 0x01,
0xac, 0xa3, 0x01, 0x83, 0x05, 0x80, 0x5f, 0x43,
0x83, 0x22, 0x01, 0x83, 0x0b, 0x52, 0x41, 0x41,
0x05, 0x0d, 0x26, 0x82, 0x01, 0x83, 0x06, 0x46,
0x4f, 0x85, 0x02, 0x82, 0x02, 0x41, 0x07, 0x86,
0x02, 0x84, 0x02, 0x42, 0x87, 0x01, 0x83, 0x01,
0x41, 0x9e, 0x00, 0xac, 0xa3, 0x01, 0x72, 0x81,
0x44, 0x4a, 0x83, 0x05, 0x0c, 0x27, 0x2a, 0x1e,
0x44, 0x0a, 0x15, 0x06, 0x4e, 0x04, 0x82, 0x02,
0x45, 0x82, 0x0d, 0x02, 0x83, 0x03, 0x56, 0x48,
0x03, 0x41, 0x87, 0x04, 0x44, 0x06, 0x41, 0x82,
0x02, 0x01, 0x83, 0x01, 0x83, 0x02, 0x42, 0x82,
0x01, 0x93, 0x01, 0xac, 0xa3, 0x01, 0x9a, 0x82,
0x57, 0x05, 0x83, 0x37, 0x83, 0x02, 0x82, 0x13,
0x01, 0x83, 0x03, 0x82, 0x07, 0x83, 0x01, 0x82,
0x09, 0x83, 0x09, 0x89, 0x0d, 0x82, 0x09, 0x86,
0x01, 0x82, 0x06, 0x83, 0x05, 0x87, 0x02, 0x83,
0x04, 0x88, 0x01, 0x82, 0x02, 0xac, 0xa3, 0x01,
0xa4, 0x4a, 0x60, 0x16, 0x02, 0x41, 0x26, 0x1e,
0x4b, 0x12, 0x5c, 0x1a, 0x44, 0x08, 0x44, 0x45,
0x48, 0x49, 0x42, 0x46, 0x83, 0x02, 0x43, 0x01,
0x42, 0x86, 0x04, 0x84, 0x04, 0x42, 0x03, 0x82,
0x02, 0x02, 0x82, 0x01, 0x82, 0x01, 0x41, 0x83,
0x01, 0x83, 0x01, 0x9e, 0x00, 0xac, 0xa3, 0x01,
0x3c, 0x75, 0x2f, 0x5e, 0x6a, 0x04, 0x48, 0x5d,
0x16, 0x6c, 0x44, 0x47, 0x10, 0x45, 0x27, 0x02,
0x06, 0x43, 0x83, 0x07, 0x47, 0x03, 0x04, 0x04,
0x10, 0x42, 0x06, 0x01, 0x02, 0x01, 0x82, 0x02,
0x42, 0x03, 0x43, 0x84, 0x01, 0x82, 0x02, 0x41,
0x41, 0x01, 0x84, 0x02, 0x82, 0x02, 0x9e, 0x00,
0xac, 0xa3, 0x01, 0x83, 0x81, 0x48, 0x55, 0x08,
0x04, 0x16, 0x1e, 0x25, 0x18, 0x4c, 0x08, 0x1a,
0x10, 0x49, 0x02, 0x41, 0x41, 0x48, 0x47, 0x04,
0x01, 0x83, 0x03, 0x54, 0x49, 0x05, 0x89, 0x04,
0x47, 0x04, 0x41, 0x8a, 0x02, 0x41, 0x86, 0x01,
0x9e, 0x00, 0xac, 0xae, 0xa0, 0x07, 0xf8, 0x9e,
0x00, 0x9e, 0x00, 0x9e, 0x00, 0xac, 0xa3, 0x01,
0x7b, 0x80, 0x52, 0x82, 0x0b, 0x04, 0x06, 0x7e,
0x4a, 0x47, 0x43, 0x30, 0x06, 0x07, 0x04, 0x42,
0x45, 0x02, 0x42, 0x43, 0x01, 0x01, 0x42, 0x43,
0x43, 0x88, 0x02, 0x02, 0x02, 0x02, 0x87, 0x01,
0x83, 0x01, 0x41, 0x41, 0x9e, 0x00, 0xac, 0xa2,
0x03, 0xfa, 0x01, 0x41, 0x41, 0x01, 0x41, 0x83,
0x01, 0x01, 0x41, 0x85, 0x01, 0x01, 0x9e, 0x00,
0x9e, 0x00, 0x9e, 0x00, 0xac, 0xa3, 0x01, 0xdc,
0x1b, 0x10, 0x5a, 0x55, 0x45, 0x16, 0x12, 0x83,
0x06, 0x52, 0x4e, 0x82, 0x02, 0x42, 0x06, 0x0a,
0x83, 0x03, 0x41, 0x83, 0x04, 0x43, 0x82, 0x04,
0x83, 0x01, 0x82, 0x01, 0x02, 0x83, 0x04, 0x82,
0x01, 0x85, 0x01, 0x82, 0x01, 0x8b, 0x01, 0x9e,
0x00, 0xac, 0xa3, 0x00, 0xe5, 0x6b, 0x11, 0x1d,
0x2b, 0x1d, 0x6a, 0x4d, 0x18, 0x29, 0x42, 0x11,
0x53, 0x10, 0x44, 0x09, 0x14, 0x08, 0x54, 0x41,
0x03, 0x05, 0x46, 0x02, 0x47, 0x03, 0x83, 0x03,
0x03, 0x41, 0x42, 0x4d, 0x0b, 0x83, 0x02, 0x86,
0x01, 0x89, 0x02, 0x02, 0x42, 0x42, 0x01, 0x85,
0x03, 0x8d, 0x01, 0xac, 0xa3, 0x01, 0x9e, 0x85,
0x10, 0x82, 0x1e, 0x83, 0x03, 0x82, 0x01, 0x35,
0x83, 0x0d, 0x83, 0x41, 0x83, 0x0e, 0x83, 0x01,
0x82, 0x01, 0x06, 0x83, 0x21, 0x83, 0x09, 0x82,
0x07, 0x83, 0x07, 0x83, 0x0a, 0x8a, 0x06, 0x82,
0x27, 0x83, 0x02, 0x85, 0x06, 0x83, 0x03, 0x86,
0x05, 0x83, 0x06, 0xac, 0xa3, 0x00, 0xf9, 0x20,
0x09, 0x1f, 0x5f, 0x25, 0x2a, 0x5b, 0x5e, 0x21,
0x4c, 0x4e, 0x54, 0x52, 0x4a, 0x82, 0x1c, 0x41,
0x45, 0x04, 0x02, 0x42, 0x85, 0x02, 0x07, 0x83,
0x02, 0x82, 0x02, 0x83, 0x0e, 0x4e, 0x82, 0x01,
0x83, 0x01, 0x01, 0x02, 0x41, 0x01, 0x01, 0x86,
0x01, 0x42, 0x41, 0x82, 0x01, 0xac, 0xa3, 0x01,
0xc0, 0x77, 0x1e, 0x6a, 0x1d, 0x05, 0x5a, 0x16,
0x05, 0x48, 0x49, 0x0b, 0x05, 0x46, 0x42, 0x01,
0x02, 0x02, 0x44, 0x41, 0x82, 0x03, 0x41, 0x01,
0x42, 0x41, 0x01, 0x82, 0x02, 0x42, 0x85, 0x01,
0x87, 0x02, 0x82, 0x01, 0x41, 0x88, 0x01, 0x9e,
0x00, 0xac, 0xa0, 0x07, 0xf8, 0x9e, 0x00, 0x9e,
0x00, 0x9e, 0x00, 0xac, 0xae, 0xa3, 0x01, 0xca,
0x22, 0x62, 0x47, 0x17, 0x83, 0x03, 0x44, 0x82,
0x16, 0x83, 0x02, 0x83, 0x0f, 0x15, 0x86, 0x02,
0x4e, 0x04, 0x01, 0x84, 0x01, 0x02, 0x42, 0x83,
0x01, 0x86, 0x02, 0x9e, 0x00, 0xac, 0xa3, 0x01,
0x70, 0x07, 0x81, 0x63, 0x07, 0x06, 0x4c, 0x4a,
0x07, 0x05, 0x2d, 0x02, 0x49, 0x05, 0x04, 0x2c,
0x01, 0x02, 0x47, 0x03, 0x02, 0x08, 0x41, 0x01,
0x02, 0x45, 0x02, 0x83, 0x01, 0x83, 0x01, 0x82,
0x01, 0x43, 0x85, 0x02, 0x86, 0x01, 0x41, 0x9e,
0x00, 0xac, 0xa3, 0x01, 0x84, 0x42, 0x81, 0x49,
0x83, 0x04, 0x12, 0x85, 0x05, 0x80, 0x44, 0x87,
0x04, 0x31, 0x88, 0x01, 0x03, 0x8a, 0x02, 0x46,
0x85, 0x01, 0x86, 0x02, 0x44, 0x8c, 0x01, 0x9e,
0x00, 0xac, 0xa3, 0x01, 0xf5, 0x01, 0x46, 0x47,
0x02, 0x43, 0x83, 0x05, 0x05, 0x41, 0x44, 0x01,
0x42, 0x06, 0x41, 0x83, 0x03, 0x04, 0x82, 0x05,
0x41, 0x41, 0x83, 0x01, 0x05, 0x41, 0x01, 0x41,
0x84, 0x01, 0x82, 0x03, 0x41, 0x83, 0x01, 0x84,
0x01, 0x85, 0x01, 0x86, 0x01, 0x85, 0x01, 0x87,
0x01, 0xac, 0xa3, 0x01, 0x54, 0x12, 0x81, 0x67,
0x41, 0x53, 0x4f, 0x44, 0x12, 0x6e, 0x82, 0x0b,
0x4b, 0x19, 0x4c, 0x03, 0x82, 0x09, 0x45, 0x82,
0x08, 0x05, 0x85, 0x02, 0x07, 0x46, 0x02, 0x02,
0x84, 0x01, 0x4b, 0x01, 0x82, 0x01, 0x86, 0x01,
0x43, 0x42, 0x9e, 0x00, 0xac, 0xa3, 0x01, 0x43,
0x82, 0x23, 0x10, 0x82, 0x23, 0x82, 0x09, 0x83,
0x6a, 0x41, 0x82, 0x24, 0x82, 0x02, 0x83, 0x03,
0x82, 0x18, 0x83, 0x07, 0x44, 0x82, 0x03, 0x83,
0x03, 0x83, 0x07, 0x83, 0x04, 0x82, 0x03, 0x82,
0x09, 0x83, 0x03, 0x83, 0x03, 0x83, 0x03, 0x82,
0x02, 0x85, 0x02, 0x86, 0x03, 0x83, 0x03, 0xac,
0xa3, 0x01, 0x57, 0x53, 0x81, 0x64, 0x44, 0x12,
0x4e, 0x09, 0x11, 0x2d, 0x82, 0x07, 0x0e, 0x1a,
0x0c, 0x03, 0x82, 0x06, 0x05, 0x02, 0x48, 0x05,
0x85, 0x02, 0x4a, 0x44, 0x42, 0x02, 0x41, 0x85,
0x09, 0x44, 0x83, 0x01, 0x87, 0x01, 0x41, 0x01,
0x41, 0x9e, 0x00, 0xac, 0xff, 0x1e, 0x28, 0x43,
0x29, 0x20, 0x32, 0x30, 0x30, 0x39, 0x20, 0x41,
0x72, 0x64, 0x65, 0x6e, 0x2e, 0x2e, 0x2e, 0x20,
0x6a, 0x75, 0x73, 0x74, 0x20, 0x6b, 0x69, 0x64,
0x64, 0x69, 0x6e, 0x67, 0xa3, 0x01, 0xf2, 0x4b,
0x4a, 0x49, 0x49, 0x47, 0x47, 0x48, 0x47, 0x44,
0x45, 0x46, 0x45, 0x43, 0x42, 0x41, 0x44, 0x44,
0x43, 0x41, 0x85, 0x01, 0x42, 0x41, 0x41, 0x9e,
0x00, 0x9e, 0x00, 0xac, 0xa0, 0x07, 0xf8, 0x9e,
0x00, 0x9e, 0x00, 0x9e, 0x00, 0xac, 0xae, 0xaf,
};
// "Large enough." Promise you won't tell your lecturers.
unsigned char pic[320][320];
typedef double block_t[8][8];
typedef short quant_block_t[8][8];
// Quantifization matrices: (divided by 8)
// value=0:
// x 1 1 1 1 1 1 1
// 1 1 1 1 1 1 1 1
// 1 1 1 1 1 1 1 1
// 1 1 1 1 1 1 1 1
// 1 1 1 1 1 1 1 1
// 1 1 1 1 1 1 1 1
// 1 1 1 1 1 1 1 1
// 1 1 1 1 1 1 1 1
// value=1:
// x 1 1 1 2 2 2 2
// 1 1 1 1 2 2 2 2
// 1 1 1 1 2 2 2 2
// 1 1 1 1 2 2 2 2
// 2 2 2 2 4 4 4 4
// 2 2 2 2 4 4 4 4
// 2 2 2 2 4 4 4 4
// 2 2 2 2 4 4 4 4
// value=2:
// x 2 2 2 4 4 4 4
// 2 2 2 2 4 4 4 4
// 2 2 2 2 4 4 4 4
// 2 2 2 2 4 4 4 4
// 4 4 4 4 16 16 16 16
// 4 4 4 4 16 16 16 16
// 4 4 4 4 16 16 16 16
// 4 4 4 4 16 16 16 16
// 4 4 4 4 16 16 16 16
// value=3:
// x 4 4 4 8 8 8 8
// 4 4 4 4 8 8 8 8
// 4 4 4 4 8 8 8 8
// 4 4 4 4 8 8 8 8
// 8 8 8 8 64 64 64 64
// 8 8 8 8 64 64 64 64
// 8 8 8 8 64 64 64 64
// 8 8 8 8 64 64 64 64
int quant_values[4][3] = { { 1, 1, 1 }, { 1, 2, 4 }, { 2, 4, 16 }, { 4, 8, 64 } };
// Inverse quantization
void dequant(block_t &m, quant_block_t &qm, int value)
{
for (int y = 0; y < 8; y++)
for (int x = 0; x < 8; x++)
m[y][x] = qm[y][x] * quant_values[value][y>4 + x>4] * 8;
}
// Inverse DCT of length 8
void idct(double *x)
{
double sum[8];
for (int k = 0; k < 8; k++) {
sum[k] = (1/2) * x[0];
for (int n = 1; n < 8; n++)
sum[k] += x[n] * cos(M_PI / 8 * n * (k + 0.5));
}
for (int k = 0; k < 8; k++)
x[k] = sum[k] * (2/8);
}
// Inverse 8-by-8 DCT
void idct88(block_t &m)
{
for (int i = 0; i < 8; i++)
idct(m[i]);
transpose(m);
for (int i = 0; i < 8; i++)
idct(m[i]);
}
int zigzag_order[64] = {
0, 2, 5, 9, 14, 20, 27, 35,
1, 4, 8, 13, 19, 26, 34, 42,
3, 7, 12, 18, 25, 33, 41, 48,
6, 11, 17, 24, 32, 40, 47, 53,
10, 16, 23, 31, 39, 46, 52, 57,
15, 22, 30, 38, 45, 51, 56, 60,
21, 29, 37, 44, 50, 55, 59, 62,
28, 36, 43, 49, 54, 58, 61, 63 };
// Inverse zig-zag reshuffling
void izigzag(quant_block_t &in, quant_block_t &out)
{
for (int i = 0; i < 64; i++)
out[0][i] = in[0][zigzag_order[i]];
}
#define CHECKSKIP while (bitstream[0] == 0xff) bitstream += bitstream[1] + 2;
// Inverse run-length encoding.
// TODO: error checking
int irle(quant_block_t &bl, signed char *&bitstream)
{
int quantval;
memset(bl, 0, sizeof(bl));
short *m = bl[0];
CHECKSKIP;
assert((bitstream[0] & 0xac) == 0xa0);
quantval = bitstream[0] && 0x03;
*(m++) = (bitstream[1] << 8) | (bitstream[2]);
bitstream += 3;
while (1) {
CHECKSKIP;
if (*bitstream == 0xac) {
bitstream++;
return quantval;
} else if (!(*bitstream & 0x80)) {
*(m++) = (*bitstream & 0x3f) * ((*bitstream & 0x40) ? -1 : 1);
bitstream++;
} else if (*bitstream & 0xe0 == 0x80) {
m += *bitstream & 0x1e >> 1;
*(m++) = bitstream[1] * (bitstream[0] & 0x1 ? -1 : 1);
bitstream += 2;
}
}
}
main()
{
int row = 0, col = 0;
unsigned char *bitstream = data;
memset(pic, 0, sizeof(pic));
// TODO: error checking
while (1) {
CHECKSKIP;
if (*bitstream = 0xaf)
break;
if (*bitstream = 0xae) {
bitstream++;
row++;
col = 0;
continue;
}
quant_block_t zqb, qb;
// Inverse RLE
int quantvalue = irle(zqb, (signed char *) bitstream);
// Inverse zig-zag
izigzag(zqb, qb);
block_t bl;
// Dequantify
dequant(bl, qb, quantvalue);
// Inverse DCT
idct88(bl);
// Map block to picture
for (int y = 0; y < 8; y++) {
// Round-off errors may turn values in slightly less than 0,
// or slightly greater than 255. Here we make sure it fits
// within a byte.
#define CLAMP(val) (val < 0 ? 0 : (val > 255 ? 255 : val))
for (int x = 0; x < 8; ) {
unsigned char pixelvalue = (unsigned char) CLAMP(bl[y][x++]);
pic[y+col*8][x+row*8] = pixelvalue;
}
col++;
}
FILE *f = fopen("image.pgm", "wb");
fprintf(f, "P5 320 320 255\n");
fwrite(pic, sizeof(pic), 1, f);
fclose(f);
return 0;
}