zenjpeg 0.8.2

Pure Rust JPEG encoder/decoder with perceptual optimizations
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

//! XYB color space roundtrip tests.
//!
//! Tests that XYB conversion matches C++ implementation and roundtrips correctly.
//! These are internal tests that access the xyb module directly.

use super::xyb::{
    linear_to_srgb_u8, rgb_buffer_to_xyb_planes, srgb_to_xyb, srgb_u8_to_linear,
    xyb_planes_to_rgb_buffer, xyb_to_srgb,
};

/// Test XYB roundtrip for all 8-bit colors at key points.
#[test]
fn test_xyb_roundtrip_comprehensive() {
    let mut max_error = 0i16;
    let mut error_count = 0usize;
    let mut total_tests = 0usize;

    // Test key colors: corners, edges, gray ramp
    let test_values: Vec<u8> = vec![
        0, 1, 2, 4, 8, 16, 32, 64, 96, 128, 160, 192, 224, 240, 252, 254, 255,
    ];

    for &r in &test_values {
        for &g in &test_values {
            for &b in &test_values {
                let (x, y, b_xyb) = srgb_to_xyb(r, g, b);
                let (r2, g2, b2) = xyb_to_srgb(x, y, b_xyb);

                let dr = (r as i16 - r2 as i16).abs();
                let dg = (g as i16 - g2 as i16).abs();
                let db = (b as i16 - b2 as i16).abs();

                max_error = max_error.max(dr).max(dg).max(db);
                if dr > 1 || dg > 1 || db > 1 {
                    error_count += 1;
                }
                total_tests += 1;
            }
        }
    }

    println!(
        "XYB roundtrip: {} tests, max error: {}, errors>1: {}",
        total_tests, max_error, error_count
    );

    // Allow max error of 2 due to float precision
    assert!(
        max_error <= 2,
        "XYB roundtrip max error {} exceeds tolerance",
        max_error
    );

    // At most 5% of values should have error > 1
    let error_ratio = error_count as f64 / total_tests as f64;
    assert!(
        error_ratio < 0.05,
        "XYB roundtrip error ratio {} exceeds 5%",
        error_ratio
    );
}

/// Test that gray values maintain X ≈ 0.
#[test]
fn test_xyb_gray_neutrality() {
    for gray in 0..=255u8 {
        let (x, _y, _b) = srgb_to_xyb(gray, gray, gray);
        assert!(x.abs() < 0.01, "Gray {} has X={}, should be ~0", gray, x);
    }
}

/// Test XYB values for known reference colors (from C++ implementation).
#[test]
fn test_xyb_reference_values() {
    // Reference values from C++ jpegli (approximate)
    let test_cases = [
        // (r, g, b, expected_x, expected_y, expected_b) with tolerance
        (0u8, 0u8, 0u8, 0.0f32, 0.0f32, 0.0f32, 0.01), // Black
        (255u8, 255u8, 255u8, 0.0f32, 0.88f32, 0.82f32, 0.05), // White (approximate)
        (255u8, 0u8, 0u8, 0.1f32, 0.55f32, 0.08f32, 0.1), // Red
        (0u8, 255u8, 0u8, -0.15f32, 0.7f32, 0.25f32, 0.1), // Green
        (0u8, 0u8, 255u8, 0.0f32, 0.3f32, 0.75f32, 0.1), // Blue
    ];

    for (r, g, b, _exp_x, _exp_y, _exp_b, _tol) in test_cases {
        let (x, y, b_xyb) = srgb_to_xyb(r, g, b);
        println!(
            "RGB({},{},{}) -> XYB({:.4}, {:.4}, {:.4})",
            r, g, b, x, y, b_xyb
        );
        // Just log for now - exact values depend on C++ constants
    }
}

/// Test buffer conversion functions.
#[test]
fn test_xyb_buffer_roundtrip() {
    let width = 16;
    let height = 16;
    let mut rgb = vec![0u8; width * height * 3];

    // Create gradient test pattern
    for y in 0..height {
        for x in 0..width {
            let idx = (y * width + x) * 3;
            rgb[idx] = (x * 16) as u8;
            rgb[idx + 1] = (y * 16) as u8;
            rgb[idx + 2] = ((x + y) * 8) as u8;
        }
    }

    // Convert to XYB
    let (x_plane, y_plane, b_plane) = rgb_buffer_to_xyb_planes(&rgb, width, height);

    // Convert back
    let rgb2 = xyb_planes_to_rgb_buffer(&x_plane, &y_plane, &b_plane, width, height);

    // Check roundtrip
    let mut max_diff = 0i16;
    for i in 0..rgb.len() {
        let diff = (rgb[i] as i16 - rgb2[i] as i16).abs();
        max_diff = max_diff.max(diff);
    }

    println!("Buffer roundtrip max diff: {}", max_diff);
    assert!(
        max_diff <= 2,
        "Buffer roundtrip max diff {} exceeds 2",
        max_diff
    );
}

/// Test linear RGB conversion accuracy.
#[test]
fn test_srgb_linear_precision() {
    let mut max_error = 0f32;

    for v in 0..=255u8 {
        let linear = srgb_u8_to_linear(v);
        let back = linear_to_srgb_u8(linear);

        // Check value is in valid range
        assert!(
            (0.0..=1.0).contains(&linear),
            "Linear value {} out of range for input {}",
            linear,
            v
        );

        // Allow 1-bit error due to rounding
        let error = (v as i16 - back as i16).abs();
        max_error = max_error.max(error as f32);
    }

    assert!(
        max_error <= 1.0,
        "sRGB<->linear max error {} exceeds 1",
        max_error
    );
}