justbig2 0.1.2

Pure Rust JBIG2 image decoder with no_std support
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
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

//! Generic Refinement Region decoder (ITU T.88 6.3, 7.4.7).
//!
//! Refines a reference image pixel-by-pixel using arithmetic coding.

use crate::arith::{ArithCx, ArithState};
use crate::error::Result;
use crate::image::Jbig2Image;

/// Refinement region parameters (Table 6).
#[derive(Debug, Clone)]
pub struct RefinementRegionParams {
    /// Template (0 or 1). Template 0: 13 contexts, Template 1: 10 contexts.
    pub gr_template: u8,
    /// Reference image.
    pub reference: Jbig2Image,
    /// Reference offset X.
    pub reference_dx: i32,
    /// Reference offset Y.
    pub reference_dy: i32,
    /// Typical Prediction on.
    pub tpgron: bool,
    /// Adaptive template pixels (4 values, only used for template 0).
    pub grat: [i8; 4],
}

/// Stats size for refinement region.
pub fn refinement_stats_size(template: u8) -> usize {
    if template != 0 { 1 << 10 } else { 1 << 13 }
}

/// Decode a generic refinement region.
pub fn decode_refinement_region(
    params: &RefinementRegionParams,
    as_: &mut ArithState,
    image: &mut Jbig2Image,
    gr_stats: &mut [ArithCx],
) -> Result<()> {
    if params.tpgron {
        return decode_refinement_tpgron(params, as_, image, gr_stats);
    }

    if params.gr_template != 0 {
        decode_refinement_template1(params, as_, image, gr_stats)
    } else {
        decode_refinement_template0(params, as_, image, gr_stats)
    }
}

// --- Template 0: 13-pixel context (3 current + 10 reference) ---

fn decode_refinement_template0(
    params: &RefinementRegionParams,
    as_: &mut ArithState,
    image: &mut Jbig2Image,
    gr_stats: &mut [ArithCx],
) -> Result<()> {
    let grw = image.width;
    let grh = image.height;
    let r = &params.reference;
    let dx = params.reference_dx;
    let dy = params.reference_dy;

    for y in 0..grh {
        for x in 0..grw {
            let ix = x as i32;
            let iy = y as i32;

            let mut context: u32 = 0;
            // Current image pixels
            context |= (image.get_pixel((ix - 1) as u32, y) as u32) << 0;
            context |= (image.get_pixel((ix + 1) as u32, (iy - 1) as u32) as u32) << 1;
            context |= (image.get_pixel(x, (iy - 1) as u32) as u32) << 2;
            // Adaptive pixel
            context |= (image.get_pixel(
                (ix + params.grat[0] as i32) as u32,
                (iy + params.grat[1] as i32) as u32,
            ) as u32) << 3;
            // Reference pixels
            context |= (r.get_pixel((ix - dx + 1) as u32, (iy - dy + 1) as u32) as u32) << 4;
            context |= (r.get_pixel((ix - dx) as u32, (iy - dy + 1) as u32) as u32) << 5;
            context |= (r.get_pixel((ix - dx - 1) as u32, (iy - dy + 1) as u32) as u32) << 6;
            context |= (r.get_pixel((ix - dx + 1) as u32, (iy - dy) as u32) as u32) << 7;
            context |= (r.get_pixel((ix - dx) as u32, (iy - dy) as u32) as u32) << 8;
            context |= (r.get_pixel((ix - dx - 1) as u32, (iy - dy) as u32) as u32) << 9;
            context |= (r.get_pixel((ix - dx + 1) as u32, (iy - dy - 1) as u32) as u32) << 10;
            context |= (r.get_pixel((ix - dx) as u32, (iy - dy - 1) as u32) as u32) << 11;
            // Adaptive reference pixel
            context |= (r.get_pixel(
                (ix - dx + params.grat[2] as i32) as u32,
                (iy - dy + params.grat[3] as i32) as u32,
            ) as u32) << 12;

            let bit = as_.decode(&mut gr_stats[context as usize])?;
            image.set_pixel(x, y, bit);
        }
    }
    Ok(())
}

// --- Template 1: 10-pixel context (4 current + 6 reference) ---

fn decode_refinement_template1(
    params: &RefinementRegionParams,
    as_: &mut ArithState,
    image: &mut Jbig2Image,
    gr_stats: &mut [ArithCx],
) -> Result<()> {
    let grw = image.width;
    let grh = image.height;
    let r = &params.reference;
    let dx = params.reference_dx;
    let dy = params.reference_dy;

    for y in 0..grh {
        for x in 0..grw {
            let ix = x as i32;
            let iy = y as i32;

            let mut context: u32 = 0;
            // Current image pixels
            context |= (image.get_pixel((ix - 1) as u32, y) as u32) << 0;
            context |= (image.get_pixel((ix + 1) as u32, (iy - 1) as u32) as u32) << 1;
            context |= (image.get_pixel(x, (iy - 1) as u32) as u32) << 2;
            context |= (image.get_pixel((ix - 1) as u32, (iy - 1) as u32) as u32) << 3;
            // Reference pixels
            context |= (r.get_pixel((ix - dx + 1) as u32, (iy - dy + 1) as u32) as u32) << 4;
            context |= (r.get_pixel((ix - dx) as u32, (iy - dy + 1) as u32) as u32) << 5;
            context |= (r.get_pixel((ix - dx + 1) as u32, (iy - dy) as u32) as u32) << 6;
            context |= (r.get_pixel((ix - dx) as u32, (iy - dy) as u32) as u32) << 7;
            context |= (r.get_pixel((ix - dx - 1) as u32, (iy - dy) as u32) as u32) << 8;
            context |= (r.get_pixel((ix - dx) as u32, (iy - dy - 1) as u32) as u32) << 9;

            let bit = as_.decode(&mut gr_stats[context as usize])?;
            image.set_pixel(x, y, bit);
        }
    }
    Ok(())
}

// --- TPGRON: Typical Prediction for Refinement ---

/// Check if pixel (i,j) in reference has all 8 neighbors with the same value.
fn implicit_value(r: &Jbig2Image, i: i32, j: i32) -> Option<u8> {
    let m = r.get_pixel(i as u32, j as u32);
    for &(dx, dy) in &[
        (-1, -1), (0, -1), (1, -1),
        (-1, 0),           (1, 0),
        (-1, 1),  (0, 1),  (1, 1),
    ] {
        if r.get_pixel((i + dx) as u32, (j + dy) as u32) != m {
            return None;
        }
    }
    Some(m)
}

fn build_context(params: &RefinementRegionParams, image: &Jbig2Image, x: u32, y: u32) -> u32 {
    let ix = x as i32;
    let iy = y as i32;
    let r = &params.reference;
    let dx = params.reference_dx;
    let dy = params.reference_dy;

    if params.gr_template != 0 {
        // Template 1
        let mut ctx: u32 = 0;
        ctx |= (image.get_pixel((ix - 1) as u32, y) as u32) << 0;
        ctx |= (image.get_pixel((ix + 1) as u32, (iy - 1) as u32) as u32) << 1;
        ctx |= (image.get_pixel(x, (iy - 1) as u32) as u32) << 2;
        ctx |= (image.get_pixel((ix - 1) as u32, (iy - 1) as u32) as u32) << 3;
        ctx |= (r.get_pixel((ix - dx + 1) as u32, (iy - dy + 1) as u32) as u32) << 4;
        ctx |= (r.get_pixel((ix - dx) as u32, (iy - dy + 1) as u32) as u32) << 5;
        ctx |= (r.get_pixel((ix - dx + 1) as u32, (iy - dy) as u32) as u32) << 6;
        ctx |= (r.get_pixel((ix - dx) as u32, (iy - dy) as u32) as u32) << 7;
        ctx |= (r.get_pixel((ix - dx - 1) as u32, (iy - dy) as u32) as u32) << 8;
        ctx |= (r.get_pixel((ix - dx) as u32, (iy - dy - 1) as u32) as u32) << 9;
        ctx
    } else {
        // Template 0
        let mut ctx: u32 = 0;
        ctx |= (image.get_pixel((ix - 1) as u32, y) as u32) << 0;
        ctx |= (image.get_pixel((ix + 1) as u32, (iy - 1) as u32) as u32) << 1;
        ctx |= (image.get_pixel(x, (iy - 1) as u32) as u32) << 2;
        ctx |= (image.get_pixel((ix + params.grat[0] as i32) as u32, (iy + params.grat[1] as i32) as u32) as u32) << 3;
        ctx |= (r.get_pixel((ix - dx + 1) as u32, (iy - dy + 1) as u32) as u32) << 4;
        ctx |= (r.get_pixel((ix - dx) as u32, (iy - dy + 1) as u32) as u32) << 5;
        ctx |= (r.get_pixel((ix - dx - 1) as u32, (iy - dy + 1) as u32) as u32) << 6;
        ctx |= (r.get_pixel((ix - dx + 1) as u32, (iy - dy) as u32) as u32) << 7;
        ctx |= (r.get_pixel((ix - dx) as u32, (iy - dy) as u32) as u32) << 8;
        ctx |= (r.get_pixel((ix - dx - 1) as u32, (iy - dy) as u32) as u32) << 9;
        ctx |= (r.get_pixel((ix - dx + 1) as u32, (iy - dy - 1) as u32) as u32) << 10;
        ctx |= (r.get_pixel((ix - dx) as u32, (iy - dy - 1) as u32) as u32) << 11;
        ctx |= (r.get_pixel((ix - dx + params.grat[2] as i32) as u32, (iy - dy + params.grat[3] as i32) as u32) as u32) << 12;
        ctx
    }
}

fn decode_refinement_tpgron(
    params: &RefinementRegionParams,
    as_: &mut ArithState,
    image: &mut Jbig2Image,
    gr_stats: &mut [ArithCx],
) -> Result<()> {
    let grw = image.width;
    let grh = image.height;
    let start_context: u32 = if params.gr_template != 0 { 0x40 } else { 0x100 };
    let mut ltp = 0u8;

    for y in 0..grh {
        let bit = as_.decode(&mut gr_stats[start_context as usize])?;
        ltp ^= bit;

        if ltp == 0 {
            // Decode row normally
            for x in 0..grw {
                let ctx = build_context(params, image, x, y);
                let bit = as_.decode(&mut gr_stats[ctx as usize])?;
                image.set_pixel(x, y, bit);
            }
        } else {
            // Use implicit values where possible
            for x in 0..grw {
                let ix = x as i32;
                let iy = y as i32;
                let ri = ix - params.reference_dx;
                let rj = iy - params.reference_dy;

                if let Some(v) = implicit_value(&params.reference, ri, rj) {
                    image.set_pixel(x, y, v);
                } else {
                    let ctx = build_context(params, image, x, y);
                    let bit = as_.decode(&mut gr_stats[ctx as usize])?;
                    image.set_pixel(x, y, bit);
                }
            }
        }
    }
    Ok(())
}