jixel 0.2.2

Tiny JPEG XL encoder
Documentation 
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

/*
 * // Copyright (c) Radzivon Bartoshyk 5/2026. All rights reserved.
 * //
 * // Redistribution and use in source and binary forms, with or without modification,
 * // are permitted provided that the following conditions are met:
 * //
 * // 1.  Redistributions of source code must retain the above copyright notice, this
 * // list of conditions and the following disclaimer.
 * //
 * // 2.  Redistributions in binary form must reproduce the above copyright notice,
 * // this list of conditions and the following disclaimer in the documentation
 * // and/or other materials provided with the distribution.
 * //
 * // 3.  Neither the name of the copyright holder nor the names of its
 * // contributors may be used to endorse or promote products derived from
 * // this software without specific prior written permission.
 * //
 * // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * // AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * // IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * // DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 * // FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * // DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * // SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * // CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * // OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

pub(crate) const K_NON_ZERO_BUCKETS: usize = 37;
pub(crate) const K_ZERO_DENSITY_CONTEXT_COUNT: usize = 458;
pub(crate) const K_NUM_BLOCK_CTXS: usize = 4;
pub(crate) const K_NUM_AC_CONTEXTS: usize =
    K_NUM_BLOCK_CTXS * (K_NON_ZERO_BUCKETS + K_ZERO_DENSITY_CONTEXT_COUNT); // 1980

pub(crate) const K_NUM_AC_STRATEGY_CODES: usize = 27;

/// Frequency-band context per zigzag position. Index 0 is unused (DC).
pub(crate) static K_COEFF_FREQ_CONTEXT: [u16; 64] = [
    0xBAD, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 15, 16, 16, 17, 17, 18, 18, 19,
    19, 20, 20, 21, 21, 22, 22, 23, 23, 23, 23, 24, 24, 24, 24, 25, 25, 25, 25, 26, 26, 26, 26, 27,
    27, 27, 27, 28, 28, 28, 28, 29, 29, 29, 29, 30, 30, 30, 30,
];

/// Remaining-nonzeros context bucket.
pub(crate) static K_COEFF_NUM_NONZERO_CONTEXT: [u16; 64] = [
    0xBAD, 0, 31, 62, 62, 93, 93, 93, 93, 123, 123, 123, 123, 152, 152, 152, 152, 152, 152, 152,
    152, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 180, 206, 206, 206, 206, 206, 206,
    206, 206, 206, 206, 206, 206, 206, 206, 206, 206, 206, 206, 206, 206, 206, 206, 206, 206, 206,
    206, 206, 206, 206, 206, 206,
];

/// Static block context map signaled in WriteDCGlobal.
pub(crate) static K_COMPACT_BLOCK_CONTEXT_MAP: [u8; 39] = [
    0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, // Y
    2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 3, // X
    2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 3, // B
];

#[rustfmt::skip]
pub(crate) static K_BLOCK_CONTEXT_MAP: [u8; 81] = [
    // X row. Position 4 = DCT16X16 (decoder ctx 2). Positions 6, 7 = DCT16X8/8X16 (ctx 3).
    2, 0, 0, 0, 2, 0, 3, 3, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    // Y row. Position 4 = DCT16X16 (decoder ctx 0). Positions 6, 7 = DCT16X8/8X16 (ctx 1).
    0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    // B row. Position 4 = DCT16X16 (decoder ctx 2). Positions 6, 7 = DCT16X8/8X16 (ctx 3).
    2, 0, 0, 0, 2, 0, 3, 3, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
];

#[inline]
pub(crate) fn block_context(c: usize, ac_strategy_code: u8) -> u32 {
    K_BLOCK_CONTEXT_MAP[c * K_NUM_AC_STRATEGY_CODES + ac_strategy_code as usize] as u32
}

#[inline]
pub(crate) fn non_zero_context(non_zeros: u32, block_ctx: u32) -> u32 {
    let bucket = if non_zeros < 8 {
        non_zeros
    } else if non_zeros >= 64 {
        36
    } else {
        4 + non_zeros / 2
    };
    bucket * K_NUM_BLOCK_CTXS as u32 + block_ctx
}

/// 8x8 specialization: covered_blocks = 1, log2_covered_blocks = 0, so
/// nonzeros_left and k pass through directly.
#[inline]
pub(crate) fn zero_density_context_8x8(nonzeros_left: usize, k: usize, prev: usize) -> usize {
    (K_COEFF_NUM_NONZERO_CONTEXT[nonzeros_left] as usize + K_COEFF_FREQ_CONTEXT[k] as usize) * 2
        + prev
}

/// General `zero_density_context` from libjxl-tiny. For 8x8 use
/// `zero_density_context_8x8`. For multi-block transforms, `covered_blocks` is
/// the number of 8x8 sub-blocks (2 for DCT16X8/DCT8X16) and `log2_covered_blocks`
/// is `log2(covered_blocks)` (1 for the rectangular pair).
#[inline]
pub(crate) fn zero_density_context(
    nonzeros_left: usize,
    k: usize,
    covered_blocks: usize,
    log2_covered_blocks: usize,
    prev: usize,
) -> usize {
    let nz = (nonzeros_left + covered_blocks - 1) >> log2_covered_blocks;
    let kk = k >> log2_covered_blocks;
    (K_COEFF_NUM_NONZERO_CONTEXT[nz] as usize + K_COEFF_FREQ_CONTEXT[kk] as usize) * 2 + prev
}

#[inline]
pub(crate) const fn zero_density_contexts_offset(block_ctx: u32) -> u32 {
    K_NUM_BLOCK_CTXS as u32 * K_NON_ZERO_BUCKETS as u32
        + K_ZERO_DENSITY_CONTEXT_COUNT as u32 * block_ctx
}

/// 8x8 zigzag order. Coefficient at zigzag position k is at raw index
/// K_COEFF_ORDER_8X8[k].
#[rustfmt::skip]
pub(crate) static K_COEFF_ORDER_8X8: [u8; 64] = [
    0,   1,   8,   16, 9,   2,   3,   10,
    17,  24,  32,  25, 18,  11,  4,   5,
    12,  19,  26,  33, 40,  48,  41,  34,
    27,  20,  13,  6,  7,   14,  21,  28,
    35,  42,  49,  56, 57,  50,  43,  36,
    29,  22,  15,  23, 30,  37,  44,  51,
    58,  59,  52,  45, 38,  31,  39,  46,
    53,  60,  61,  54, 47,  55,  62,  63,
];

/// 16x8 / 8x16 coefficient order (shared, libjxl-tiny `kCoeffOrders` offset 64).
/// 128 entries. Positions 0 and 1 are LF positions; HF positions are zigzagged
/// over the 16x8 grid.
#[rustfmt::skip]
pub(crate) static K_COEFF_ORDER_16X8: [u8; 128] = [
    0,   1,   16,  2,   3,   17,  32,  18,  4,   5,   19,
    33,  48,  34,  20,  6,   7,   21,  35,  49,  64,  50,  36,  22,  8,   9,
    23,  37,  51,  65,  80,  66,  52,  38,  24,  10,  11,  25,  39,  53,  67,
    81,  96,  82,  68,  54,  40,  26,  12,  13,  27,  41,  55,  69,  83,  97,
    112, 98,  84,  70,  56,  42,  28,  14,  15,  29,  43,  57,  71,  85,  99,
    113, 114, 100, 86,  72,  58,  44,  30,  31,  45,  59,  73,  87,  101, 115,
    116, 102, 88,  74,  60,  46,  47,  61,  75,  89,  103, 117, 118, 104, 90,
    76,  62,  63,  77,  91,  105, 119, 120, 106, 92,  78,  79,  93,  107, 121,
    122, 108, 94,  95,  109, 123, 124, 110, 111, 125, 126, 127,
];

#[rustfmt::skip]
pub(crate) static  K_COEFF_ORDER_16X16: [u8; 256] = [
       0,    1,   16,   17,   32,    2,    3,   18,
      33,   48,   64,   49,   34,   19,    4,    5,
      20,   35,   50,   65,   80,   96,   81,   66,
      51,   36,   21,    6,    7,   22,   37,   52,
      67,   82,   97,  112,  128,  113,   98,   83,
      68,   53,   38,   23,    8,    9,   24,   39,
      54,   69,   84,   99,  114,  129,  144,  160,
     145,  130,  115,  100,   85,   70,   55,   40,
      25,   10,   11,   26,   41,   56,   71,   86,
     101,  116,  131,  146,  161,  176,  192,  177,
     162,  147,  132,  117,  102,   87,   72,   57,
      42,   27,   12,   13,   28,   43,   58,   73,
      88,  103,  118,  133,  148,  163,  178,  193,
     208,  224,  209,  194,  179,  164,  149,  134,
     119,  104,   89,   74,   59,   44,   29,   14,
      15,   30,   45,   60,   75,   90,  105,  120,
     135,  150,  165,  180,  195,  210,  225,  240,
     241,  226,  211,  196,  181,  166,  151,  136,
     121,  106,   91,   76,   61,   46,   31,   47,
      62,   77,   92,  107,  122,  137,  152,  167,
     182,  197,  212,  227,  242,  243,  228,  213,
     198,  183,  168,  153,  138,  123,  108,   93,
      78,   63,   79,   94,  109,  124,  139,  154,
     169,  184,  199,  214,  229,  244,  245,  230,
     215,  200,  185,  170,  155,  140,  125,  110,
      95,  111,  126,  141,  156,  171,  186,  201,
     216,  231,  246,  247,  232,  217,  202,  187,
     172,  157,  142,  127,  143,  158,  173,  188,
     203,  218,  233,  248,  249,  234,  219,  204,
     189,  174,  159,  175,  190,  205,  220,  235,
     250,  251,  236,  221,  206,  191,  207,  222,
     237,  252,  253,  238,  223,  239,  254,  255,
];