CCSDS 122.0-B Image Data Compression
idc: extract test_idc suite, drop test_/find_/make_ prefixes
- Move every test case from test/test.ml into test/test_idc.ml,
drop the redundant test_ prefix on each (E325/E331), and reduce the
runner to a single Alcotest.run line (E600).
- idc.ml: rename make_2d -> array_2d and find_max_abs -> max_abs (E331).
- Replace the catch-all (with _ -> ()) in the fuzz decompress safety
test with Invalid_argument / Failure handlers (E311).
- Rename fuzz_compress.{ml,mli} to fuzz_idc.{ml,mli} and the fuzz
suite from "compress" to "idc" so E710/E720 see a corresponding
library module.
+280
-279
+1
-1
fuzz/dune
+1
-1
fuzz/dune
+1
-1
fuzz/fuzz.ml
+1
-1
fuzz/fuzz.ml
+2
-2
fuzz/fuzz_compress.ml
fuzz/fuzz_idc.ml
+2
-2
fuzz/fuzz_compress.ml
fuzz/fuzz_idc.ml
···
28
28
try
29
29
let _ = Idc.decompress ~width:8 ~height:8 data in
30
30
()
31
-
with _ -> ()
31
+
with Invalid_argument _ | Failure _ -> ()
32
32
33
33
(** Compressed output must be deterministic. *)
34
34
let test_deterministic buf =
···
47
47
if c1 <> c2 then fail "compression is not deterministic"
48
48
49
49
let suite =
50
-
( "compress",
50
+
( "idc",
51
51
[
52
52
test_case "roundtrip 8x8" [ bytes ] test_roundtrip_small;
53
53
test_case "decompress crash safety" [ bytes ] test_decompress_crash_safety;
fuzz/fuzz_compress.mli
fuzz/fuzz_idc.mli
fuzz/fuzz_compress.mli
fuzz/fuzz_idc.mli
+7
-7
lib/idc.ml
+7
-7
lib/idc.ml
···
83
83
84
84
(* ---- 2D array helpers ---- *)
85
85
86
-
let make_2d rows cols init = Array.init rows (fun _ -> Array.make cols init)
86
+
let array_2d rows cols init = Array.init rows (fun _ -> Array.make cols init)
87
87
88
88
let image_to_2d ~width ~height (data : bytes) =
89
-
let arr = make_2d height width 0 in
89
+
let arr = array_2d height width 0 in
90
90
for y = 0 to height - 1 do
91
91
for x = 0 to width - 1 do
92
92
arr.(y).(x) <- Char.code (Bytes.get data ((y * width) + x))
···
458
458
459
459
(** Quantize float coefficients to integers by rounding. *)
460
460
let quantize_2d (arr : float array array) rows cols =
461
-
let result = make_2d rows cols 0 in
461
+
let result = array_2d rows cols 0 in
462
462
for y = 0 to rows - 1 do
463
463
for x = 0 to cols - 1 do
464
464
result.(y).(x) <- Float.to_int (Float.round arr.(y).(x))
···
484
484
of (1 + mag_bits) bits. For images where the DWT produces many zero detail
485
485
coefficients, this gives significant savings. *)
486
486
487
-
let find_max_abs arr rows cols =
487
+
let max_abs arr rows cols =
488
488
let m = ref 0 in
489
489
for y = 0 to rows - 1 do
490
490
for x = 0 to cols - 1 do
···
510
510
511
511
let encode_coefficients ~wavelet ~width ~height arr =
512
512
let bw = Bitstream.create (width * height) in
513
-
let max_mag = find_max_abs arr height width in
513
+
let max_mag = max_abs arr height width in
514
514
let mag_bits = bits_needed max_mag in
515
515
(* Header *)
516
516
Bitstream.write_bits bw 16 width;
···
545
545
let wavelet = wavelet_of_id (Bitstream.read_bits br 8) in
546
546
let max_mag = Bitstream.read_bits br 16 in
547
547
let mag_bits = bits_needed max_mag in
548
-
let arr = make_2d height width 0 in
548
+
let arr = array_2d height width 0 in
549
549
(* Read zero map *)
550
-
let is_nonzero = make_2d height width false in
550
+
let is_nonzero = array_2d height width false in
551
551
for y = 0 to height - 1 do
552
552
for x = 0 to width - 1 do
553
553
is_nonzero.(y).(x) <- Bitstream.read_bits br 1 = 1
+1
-268
test/test.ml
+1
-268
test/test.ml
···
1
-
(* Copyright (c) 2026 Thomas Gazagnaire <thomas@gazagnaire.org>
2
-
3
-
Permission to use, copy, modify, and distribute this software for any
4
-
purpose with or without fee is hereby granted, provided that the above
5
-
copyright notice and this permission notice appear in all copies.
6
-
7
-
THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
8
-
WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
9
-
MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
10
-
ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
11
-
WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
12
-
ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
13
-
OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. *)
14
-
15
-
let check_roundtrip ~width ~height data =
16
-
let compressed = Idc.compress ~wavelet:`Int_5_3 ~width ~height data in
17
-
let decompressed = Idc.decompress ~width ~height compressed in
18
-
if data <> decompressed then
19
-
Alcotest.failf
20
-
"roundtrip failed: input and output differ (width=%d height=%d)" width
21
-
height
22
-
23
-
(* Constant image: all pixels the same value. *)
24
-
let test_constant_8x8 () =
25
-
let width = 8 and height = 8 in
26
-
let data = Bytes.make (width * height) '\x80' in
27
-
check_roundtrip ~width ~height data
28
-
29
-
(* Gradient image: pixel values increase left to right. *)
30
-
let test_gradient_8x8 () =
31
-
let width = 8 and height = 8 in
32
-
let data = Bytes.create (width * height) in
33
-
for y = 0 to height - 1 do
34
-
for x = 0 to width - 1 do
35
-
Bytes.set data ((y * width) + x) (Char.chr (x * 32))
36
-
done
37
-
done;
38
-
check_roundtrip ~width ~height data
39
-
40
-
(* Checkerboard pattern. *)
41
-
let test_checkerboard_8x8 () =
42
-
let width = 8 and height = 8 in
43
-
let data = Bytes.create (width * height) in
44
-
for y = 0 to height - 1 do
45
-
for x = 0 to width - 1 do
46
-
let v = if (x + y) mod 2 = 0 then 255 else 0 in
47
-
Bytes.set data ((y * width) + x) (Char.chr v)
48
-
done
49
-
done;
50
-
check_roundtrip ~width ~height data
51
-
52
-
(* 16x16 gradient roundtrip. *)
53
-
let test_gradient_16x16 () =
54
-
let width = 16 and height = 16 in
55
-
let data = Bytes.create (width * height) in
56
-
for y = 0 to height - 1 do
57
-
for x = 0 to width - 1 do
58
-
let v = ((x * 16) + (y * 16)) mod 256 in
59
-
Bytes.set data ((y * width) + x) (Char.chr v)
60
-
done
61
-
done;
62
-
check_roundtrip ~width ~height data
63
-
64
-
(* All zeros. *)
65
-
let test_zeros_8x8 () =
66
-
let width = 8 and height = 8 in
67
-
let data = Bytes.make (width * height) '\x00' in
68
-
check_roundtrip ~width ~height data
69
-
70
-
(* All 255. *)
71
-
let test_max_8x8 () =
72
-
let width = 8 and height = 8 in
73
-
let data = Bytes.make (width * height) '\xff' in
74
-
check_roundtrip ~width ~height data
75
-
76
-
(* Single pixel variations. *)
77
-
let test_single_bright_pixel () =
78
-
let width = 8 and height = 8 in
79
-
let data = Bytes.make (width * height) '\x00' in
80
-
Bytes.set data 27 '\xff';
81
-
check_roundtrip ~width ~height data
82
-
83
-
(* Verify compression ratio < 1.0 for a piecewise-constant "blocky" image.
84
-
Natural images have large regions of similar intensity separated by edges.
85
-
After DWT, most detail coefficients are zero except near edges, giving
86
-
excellent compression. *)
87
-
let test_compression_ratio_blocky () =
88
-
let width = 64 and height = 64 in
89
-
let data = Bytes.create (width * height) in
90
-
(* Four quadrants with different constant values *)
91
-
for y = 0 to height - 1 do
92
-
for x = 0 to width - 1 do
93
-
let v =
94
-
if y < 32 then if x < 32 then 40 else 120
95
-
else if x < 32 then 180
96
-
else 220
97
-
in
98
-
Bytes.set data ((y * width) + x) (Char.chr v)
99
-
done
100
-
done;
101
-
let compressed = Idc.compress ~wavelet:`Int_5_3 ~width ~height data in
102
-
let decompressed = Idc.decompress ~width ~height compressed in
103
-
if data <> decompressed then Alcotest.fail "blocky image roundtrip failed";
104
-
let ratio =
105
-
Float.of_int (Bytes.length compressed) /. Float.of_int (Bytes.length data)
106
-
in
107
-
if ratio >= 1.0 then
108
-
Alcotest.failf
109
-
"compression ratio %.3f >= 1.0 for blocky 64x64 image (compressed=%d, \
110
-
original=%d)"
111
-
ratio (Bytes.length compressed) (Bytes.length data)
112
-
113
-
(* Larger piecewise-constant image should compress even better. *)
114
-
let test_compression_ratio_large_blocky () =
115
-
let width = 128 and height = 128 in
116
-
let data = Bytes.create (width * height) in
117
-
(* Horizontal stripes *)
118
-
for y = 0 to height - 1 do
119
-
let v = y / 32 * 60 in
120
-
for x = 0 to width - 1 do
121
-
Bytes.set data ((y * width) + x) (Char.chr v)
122
-
done
123
-
done;
124
-
let compressed = Idc.compress ~wavelet:`Int_5_3 ~width ~height data in
125
-
let decompressed = Idc.decompress ~width ~height compressed in
126
-
if data <> decompressed then
127
-
Alcotest.fail "large blocky image roundtrip failed";
128
-
let ratio =
129
-
Float.of_int (Bytes.length compressed) /. Float.of_int (Bytes.length data)
130
-
in
131
-
if ratio >= 1.0 then
132
-
Alcotest.failf
133
-
"compression ratio %.3f >= 1.0 for blocky 128x128 image (compressed=%d, \
134
-
original=%d)"
135
-
ratio (Bytes.length compressed) (Bytes.length data)
136
-
137
-
(* Roundtrip for non-power-of-2 dimensions. *)
138
-
let test_non_power_of_2 () =
139
-
let test_size w h =
140
-
let data = Bytes.create (w * h) in
141
-
for i = 0 to (w * h) - 1 do
142
-
Bytes.set data i (Char.chr (i mod 256))
143
-
done;
144
-
check_roundtrip ~width:w ~height:h data
145
-
in
146
-
test_size 4 4;
147
-
test_size 4 8;
148
-
test_size 6 10;
149
-
test_size 12 12;
150
-
test_size 12 20
151
-
152
-
(* Invalid input size should raise. *)
153
-
let test_invalid_size () =
154
-
let width = 8 and height = 8 in
155
-
let data = Bytes.make 10 '\x00' in
156
-
match Idc.compress ~width ~height data with
157
-
| _ -> Alcotest.fail "expected Invalid_argument for wrong data size"
158
-
| exception Invalid_argument _ -> ()
159
-
160
-
(* ---- Float 9/7 tests ---- *)
161
-
162
-
(** Compute PSNR between two byte images. *)
163
-
let psnr (a : bytes) (b : bytes) =
164
-
let n = Bytes.length a in
165
-
assert (n = Bytes.length b);
166
-
let mse = ref 0.0 in
167
-
for i = 0 to n - 1 do
168
-
let d =
169
-
Float.of_int (Char.code (Bytes.get a i))
170
-
-. Float.of_int (Char.code (Bytes.get b i))
171
-
in
172
-
mse := !mse +. (d *. d)
173
-
done;
174
-
mse := !mse /. Float.of_int n;
175
-
if !mse = 0.0 then infinity else 10.0 *. Float.log10 (255.0 *. 255.0 /. !mse)
176
-
177
-
(* Float 9/7 roundtrip: compress then decompress, check PSNR > 40 dB. *)
178
-
let test_float_97_roundtrip () =
179
-
let width = 64 and height = 64 in
180
-
let data = Bytes.create (width * height) in
181
-
(* Smooth gradient with slight sine modulation *)
182
-
for y = 0 to height - 1 do
183
-
for x = 0 to width - 1 do
184
-
let fx = Float.of_int x /. Float.of_int width in
185
-
let fy = Float.of_int y /. Float.of_int height in
186
-
let v = (fx +. fy) /. 2.0 in
187
-
let v = v +. (0.1 *. Float.sin (fx *. 6.283)) in
188
-
let v = max 0.0 (min 1.0 v) in
189
-
Bytes.set data ((y * width) + x) (Char.chr (Float.to_int (v *. 255.0)))
190
-
done
191
-
done;
192
-
let compressed = Idc.compress ~wavelet:`Float_9_7 ~width ~height data in
193
-
let decompressed = Idc.decompress ~width ~height compressed in
194
-
let p = psnr data decompressed in
195
-
if p < 40.0 then
196
-
Alcotest.failf "Float 9/7 roundtrip PSNR %.1f dB < 40 dB threshold" p
197
-
198
-
(* Float 9/7 constant image should be exact (or near-exact). *)
199
-
let test_float_97_constant () =
200
-
let width = 8 and height = 8 in
201
-
let data = Bytes.make (width * height) '\x80' in
202
-
let compressed = Idc.compress ~wavelet:`Float_9_7 ~width ~height data in
203
-
let decompressed = Idc.decompress ~width ~height compressed in
204
-
if data <> decompressed then
205
-
Alcotest.fail "Float 9/7 constant image roundtrip not exact"
206
-
207
-
(* Float 9/7 should compress a smooth non-linear image better than Int 5/3.
208
-
209
-
The CDF 9/7 wavelet has more vanishing moments than 5/3 (4 vs 2 for the
210
-
analysis filter). This means it annihilates higher-degree polynomials,
211
-
producing smaller detail coefficients for smooth signals. For a cosine wave
212
-
image, the 9/7 high-frequency coefficients round to zero more often than the
213
-
5/3 integer coefficients, giving a smaller compressed output. *)
214
-
let test_float_97_better_compression () =
215
-
let width = 64 and height = 64 in
216
-
let data = Bytes.create (width * height) in
217
-
(* Smooth cosine pattern -- not piecewise linear *)
218
-
for y = 0 to height - 1 do
219
-
for x = 0 to width - 1 do
220
-
let fx = Float.of_int x /. Float.of_int width in
221
-
let fy = Float.of_int y /. Float.of_int height in
222
-
let v =
223
-
0.5
224
-
+. (0.3 *. Float.cos (fx *. Float.pi *. 2.0))
225
-
+. (0.15 *. Float.cos (fy *. Float.pi *. 4.0))
226
-
in
227
-
let v = max 0.0 (min 1.0 v) in
228
-
Bytes.set data ((y * width) + x) (Char.chr (Float.to_int (v *. 255.0)))
229
-
done
230
-
done;
231
-
let c53 = Idc.compress ~wavelet:`Int_5_3 ~width ~height data in
232
-
let c97 = Idc.compress ~wavelet:`Float_9_7 ~width ~height data in
233
-
let r53 =
234
-
Float.of_int (Bytes.length c53) /. Float.of_int (Bytes.length data)
235
-
in
236
-
let r97 =
237
-
Float.of_int (Bytes.length c97) /. Float.of_int (Bytes.length data)
238
-
in
239
-
if r97 >= r53 then
240
-
Alcotest.failf
241
-
"Float 9/7 compression ratio %.3f >= Int 5/3 ratio %.3f for smooth \
242
-
cosine image"
243
-
r97 r53
244
-
245
-
let suite =
246
-
( "idc",
247
-
[
248
-
("constant 8x8 roundtrip", `Quick, test_constant_8x8);
249
-
("gradient 8x8 roundtrip", `Quick, test_gradient_8x8);
250
-
("checkerboard 8x8 roundtrip", `Quick, test_checkerboard_8x8);
251
-
("gradient 16x16 roundtrip", `Quick, test_gradient_16x16);
252
-
("zeros 8x8 roundtrip", `Quick, test_zeros_8x8);
253
-
("max 8x8 roundtrip", `Quick, test_max_8x8);
254
-
("single bright pixel roundtrip", `Quick, test_single_bright_pixel);
255
-
("compression ratio blocky 64x64", `Quick, test_compression_ratio_blocky);
256
-
( "compression ratio blocky 128x128",
257
-
`Quick,
258
-
test_compression_ratio_large_blocky );
259
-
("non-power-of-2 dimensions", `Quick, test_non_power_of_2);
260
-
("invalid input size", `Quick, test_invalid_size);
261
-
("float 9/7 roundtrip PSNR", `Quick, test_float_97_roundtrip);
262
-
("float 9/7 constant exact", `Quick, test_float_97_constant);
263
-
( "float 9/7 better compression than 5/3",
264
-
`Quick,
265
-
test_float_97_better_compression );
266
-
] )
267
-
268
-
let () = Alcotest.run "idc" [ suite ]
1
+
let () = Alcotest.run "idc" [ Test_idc.suite ]
+264
test/test_idc.ml
+264
test/test_idc.ml
···
1
+
(* Copyright (c) 2026 Thomas Gazagnaire <thomas@gazagnaire.org>
2
+
3
+
Permission to use, copy, modify, and distribute this software for any
4
+
purpose with or without fee is hereby granted, provided that the above
5
+
copyright notice and this permission notice appear in all copies.
6
+
7
+
THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
8
+
WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
9
+
MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
10
+
ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
11
+
WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
12
+
ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
13
+
OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. *)
14
+
15
+
let check_roundtrip ~width ~height data =
16
+
let compressed = Idc.compress ~wavelet:`Int_5_3 ~width ~height data in
17
+
let decompressed = Idc.decompress ~width ~height compressed in
18
+
if data <> decompressed then
19
+
Alcotest.failf
20
+
"roundtrip failed: input and output differ (width=%d height=%d)" width
21
+
height
22
+
23
+
(* Constant image: all pixels the same value. *)
24
+
let constant_8x8 () =
25
+
let width = 8 and height = 8 in
26
+
let data = Bytes.make (width * height) '\x80' in
27
+
check_roundtrip ~width ~height data
28
+
29
+
(* Gradient image: pixel values increase left to right. *)
30
+
let gradient_8x8 () =
31
+
let width = 8 and height = 8 in
32
+
let data = Bytes.create (width * height) in
33
+
for y = 0 to height - 1 do
34
+
for x = 0 to width - 1 do
35
+
Bytes.set data ((y * width) + x) (Char.chr (x * 32))
36
+
done
37
+
done;
38
+
check_roundtrip ~width ~height data
39
+
40
+
(* Checkerboard pattern. *)
41
+
let checkerboard_8x8 () =
42
+
let width = 8 and height = 8 in
43
+
let data = Bytes.create (width * height) in
44
+
for y = 0 to height - 1 do
45
+
for x = 0 to width - 1 do
46
+
let v = if (x + y) mod 2 = 0 then 255 else 0 in
47
+
Bytes.set data ((y * width) + x) (Char.chr v)
48
+
done
49
+
done;
50
+
check_roundtrip ~width ~height data
51
+
52
+
(* 16x16 gradient roundtrip. *)
53
+
let gradient_16x16 () =
54
+
let width = 16 and height = 16 in
55
+
let data = Bytes.create (width * height) in
56
+
for y = 0 to height - 1 do
57
+
for x = 0 to width - 1 do
58
+
let v = ((x * 16) + (y * 16)) mod 256 in
59
+
Bytes.set data ((y * width) + x) (Char.chr v)
60
+
done
61
+
done;
62
+
check_roundtrip ~width ~height data
63
+
64
+
(* All zeros. *)
65
+
let zeros_8x8 () =
66
+
let width = 8 and height = 8 in
67
+
let data = Bytes.make (width * height) '\x00' in
68
+
check_roundtrip ~width ~height data
69
+
70
+
(* All 255. *)
71
+
let max_8x8 () =
72
+
let width = 8 and height = 8 in
73
+
let data = Bytes.make (width * height) '\xff' in
74
+
check_roundtrip ~width ~height data
75
+
76
+
(* Single pixel variations. *)
77
+
let single_bright_pixel () =
78
+
let width = 8 and height = 8 in
79
+
let data = Bytes.make (width * height) '\x00' in
80
+
Bytes.set data 27 '\xff';
81
+
check_roundtrip ~width ~height data
82
+
83
+
(* Verify compression ratio < 1.0 for a piecewise-constant "blocky" image.
84
+
Natural images have large regions of similar intensity separated by edges.
85
+
After DWT, most detail coefficients are zero except near edges, giving
86
+
excellent compression. *)
87
+
let compression_ratio_blocky () =
88
+
let width = 64 and height = 64 in
89
+
let data = Bytes.create (width * height) in
90
+
for y = 0 to height - 1 do
91
+
for x = 0 to width - 1 do
92
+
let v =
93
+
if y < 32 then if x < 32 then 40 else 120
94
+
else if x < 32 then 180
95
+
else 220
96
+
in
97
+
Bytes.set data ((y * width) + x) (Char.chr v)
98
+
done
99
+
done;
100
+
let compressed = Idc.compress ~wavelet:`Int_5_3 ~width ~height data in
101
+
let decompressed = Idc.decompress ~width ~height compressed in
102
+
if data <> decompressed then Alcotest.fail "blocky image roundtrip failed";
103
+
let ratio =
104
+
Float.of_int (Bytes.length compressed) /. Float.of_int (Bytes.length data)
105
+
in
106
+
if ratio >= 1.0 then
107
+
Alcotest.failf
108
+
"compression ratio %.3f >= 1.0 for blocky 64x64 image (compressed=%d, \
109
+
original=%d)"
110
+
ratio (Bytes.length compressed) (Bytes.length data)
111
+
112
+
(* Larger piecewise-constant image should compress even better. *)
113
+
let compression_ratio_large_blocky () =
114
+
let width = 128 and height = 128 in
115
+
let data = Bytes.create (width * height) in
116
+
for y = 0 to height - 1 do
117
+
let v = y / 32 * 60 in
118
+
for x = 0 to width - 1 do
119
+
Bytes.set data ((y * width) + x) (Char.chr v)
120
+
done
121
+
done;
122
+
let compressed = Idc.compress ~wavelet:`Int_5_3 ~width ~height data in
123
+
let decompressed = Idc.decompress ~width ~height compressed in
124
+
if data <> decompressed then
125
+
Alcotest.fail "large blocky image roundtrip failed";
126
+
let ratio =
127
+
Float.of_int (Bytes.length compressed) /. Float.of_int (Bytes.length data)
128
+
in
129
+
if ratio >= 1.0 then
130
+
Alcotest.failf
131
+
"compression ratio %.3f >= 1.0 for blocky 128x128 image (compressed=%d, \
132
+
original=%d)"
133
+
ratio (Bytes.length compressed) (Bytes.length data)
134
+
135
+
(* Roundtrip for non-power-of-2 dimensions. *)
136
+
let non_power_of_2 () =
137
+
let try_size w h =
138
+
let data = Bytes.create (w * h) in
139
+
for i = 0 to (w * h) - 1 do
140
+
Bytes.set data i (Char.chr (i mod 256))
141
+
done;
142
+
check_roundtrip ~width:w ~height:h data
143
+
in
144
+
try_size 4 4;
145
+
try_size 4 8;
146
+
try_size 6 10;
147
+
try_size 12 12;
148
+
try_size 12 20
149
+
150
+
(* Invalid input size should raise. *)
151
+
let invalid_size () =
152
+
let width = 8 and height = 8 in
153
+
let data = Bytes.make 10 '\x00' in
154
+
match Idc.compress ~width ~height data with
155
+
| _ -> Alcotest.fail "expected Invalid_argument for wrong data size"
156
+
| exception Invalid_argument _ -> ()
157
+
158
+
(* ---- Float 9/7 tests ---- *)
159
+
160
+
(** Compute PSNR between two byte images. *)
161
+
let psnr (a : bytes) (b : bytes) =
162
+
let n = Bytes.length a in
163
+
assert (n = Bytes.length b);
164
+
let mse = ref 0.0 in
165
+
for i = 0 to n - 1 do
166
+
let d =
167
+
Float.of_int (Char.code (Bytes.get a i))
168
+
-. Float.of_int (Char.code (Bytes.get b i))
169
+
in
170
+
mse := !mse +. (d *. d)
171
+
done;
172
+
mse := !mse /. Float.of_int n;
173
+
if !mse = 0.0 then infinity else 10.0 *. Float.log10 (255.0 *. 255.0 /. !mse)
174
+
175
+
(* Float 9/7 roundtrip: compress then decompress, check PSNR > 40 dB. *)
176
+
let float_97_roundtrip () =
177
+
let width = 64 and height = 64 in
178
+
let data = Bytes.create (width * height) in
179
+
for y = 0 to height - 1 do
180
+
for x = 0 to width - 1 do
181
+
let fx = Float.of_int x /. Float.of_int width in
182
+
let fy = Float.of_int y /. Float.of_int height in
183
+
let v = (fx +. fy) /. 2.0 in
184
+
let v = v +. (0.1 *. Float.sin (fx *. 6.283)) in
185
+
let v = max 0.0 (min 1.0 v) in
186
+
Bytes.set data ((y * width) + x) (Char.chr (Float.to_int (v *. 255.0)))
187
+
done
188
+
done;
189
+
let compressed = Idc.compress ~wavelet:`Float_9_7 ~width ~height data in
190
+
let decompressed = Idc.decompress ~width ~height compressed in
191
+
let p = psnr data decompressed in
192
+
if p < 40.0 then
193
+
Alcotest.failf "Float 9/7 roundtrip PSNR %.1f dB < 40 dB threshold" p
194
+
195
+
(* Float 9/7 constant image should be exact (or near-exact). *)
196
+
let float_97_constant () =
197
+
let width = 8 and height = 8 in
198
+
let data = Bytes.make (width * height) '\x80' in
199
+
let compressed = Idc.compress ~wavelet:`Float_9_7 ~width ~height data in
200
+
let decompressed = Idc.decompress ~width ~height compressed in
201
+
if data <> decompressed then
202
+
Alcotest.fail "Float 9/7 constant image roundtrip not exact"
203
+
204
+
(* Float 9/7 should compress a smooth non-linear image better than Int 5/3.
205
+
206
+
The CDF 9/7 wavelet has more vanishing moments than 5/3 (4 vs 2 for the
207
+
analysis filter). This means it annihilates higher-degree polynomials,
208
+
producing smaller detail coefficients for smooth signals. For a cosine
209
+
wave image, the 9/7 high-frequency coefficients round to zero more often
210
+
than the 5/3 integer coefficients, giving a smaller compressed output. *)
211
+
let float_97_better_compression () =
212
+
let width = 64 and height = 64 in
213
+
let data = Bytes.create (width * height) in
214
+
for y = 0 to height - 1 do
215
+
for x = 0 to width - 1 do
216
+
let fx = Float.of_int x /. Float.of_int width in
217
+
let fy = Float.of_int y /. Float.of_int height in
218
+
let v =
219
+
0.5
220
+
+. (0.3 *. Float.cos (fx *. Float.pi *. 2.0))
221
+
+. (0.15 *. Float.cos (fy *. Float.pi *. 4.0))
222
+
in
223
+
let v = max 0.0 (min 1.0 v) in
224
+
Bytes.set data ((y * width) + x) (Char.chr (Float.to_int (v *. 255.0)))
225
+
done
226
+
done;
227
+
let c53 = Idc.compress ~wavelet:`Int_5_3 ~width ~height data in
228
+
let c97 = Idc.compress ~wavelet:`Float_9_7 ~width ~height data in
229
+
let r53 =
230
+
Float.of_int (Bytes.length c53) /. Float.of_int (Bytes.length data)
231
+
in
232
+
let r97 =
233
+
Float.of_int (Bytes.length c97) /. Float.of_int (Bytes.length data)
234
+
in
235
+
if r97 >= r53 then
236
+
Alcotest.failf
237
+
"Float 9/7 compression ratio %.3f >= Int 5/3 ratio %.3f for smooth \
238
+
cosine image"
239
+
r97 r53
240
+
241
+
let suite =
242
+
( "idc",
243
+
List.map
244
+
(fun (n, sp, f) -> Alcotest.test_case n sp f)
245
+
[
246
+
("constant 8x8 roundtrip", `Quick, constant_8x8);
247
+
("gradient 8x8 roundtrip", `Quick, gradient_8x8);
248
+
("checkerboard 8x8 roundtrip", `Quick, checkerboard_8x8);
249
+
("gradient 16x16 roundtrip", `Quick, gradient_16x16);
250
+
("zeros 8x8 roundtrip", `Quick, zeros_8x8);
251
+
("max 8x8 roundtrip", `Quick, max_8x8);
252
+
("single bright pixel roundtrip", `Quick, single_bright_pixel);
253
+
("compression ratio blocky 64x64", `Quick, compression_ratio_blocky);
254
+
( "compression ratio blocky 128x128",
255
+
`Quick,
256
+
compression_ratio_large_blocky );
257
+
("non-power-of-2 dimensions", `Quick, non_power_of_2);
258
+
("invalid input size", `Quick, invalid_size);
259
+
("float 9/7 roundtrip PSNR", `Quick, float_97_roundtrip);
260
+
("float 9/7 constant exact", `Quick, float_97_constant);
261
+
( "float 9/7 better compression than 5/3",
262
+
`Quick,
263
+
float_97_better_compression );
264
+
] )