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fix(extractor): Fix TJ space detection for Type3 fonts with non-standard scale

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Type3 fonts with FontMatrix [1,0,0,-1,0,0] (units_scale=1.0) had
broken word spacing: intra-word kerns of -4000 exceeded the clamped
threshold of 200, producing "Op en-Domain", "comp etition", etc.

Two fixes:
- Compute space_width fallback after units_scale is known; for
  non-standard scales, estimate from average glyph width (~45%)
  instead of the hardcoded 250 (calibrated for 1/1000-unit fonts)
- Remove upper clamp on space threshold (200 was too low for fonts
  where TJ values naturally range into thousands)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
This commit is contained in:
Abimael Martell
2026-02-16 18:56:24 -08:00
co-authored by Claude Opus 4.6
parent 2b0e6b4153
commit 8a0e6a7d6f
1 changed files with 16 additions and 7 deletions
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src/extractor.rs
+16 -7
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@@ -154,11 +154,6 @@ fn parse_simple_font_widths(
widths.insert(code, w);
}
// If space width wasn't found in the table, use a reasonable default
if space_width == 0 {
space_width = 250;
}
// Determine units_scale: for Type3 fonts, use FontMatrix[0]; for others, use 1/1000
let units_scale = if let Ok(fm) = font_dict.get(b"FontMatrix") {
if let Some(arr) = resolve_array(doc, fm) {
@@ -178,6 +173,20 @@ fn parse_simple_font_widths(
0.001 // Standard 1000-unit system
};
// If space width wasn't found in the table, estimate from font metrics.
// The default of 250 is calibrated for standard 1000-unit fonts (units_scale=0.001).
// For Type3 fonts with different coordinate systems, use average glyph width instead.
if space_width == 0 {
if !widths.is_empty() && (units_scale - 0.001).abs() > 0.0005 {
// Non-standard scale: estimate space as ~45% of average glyph width
let sum: u32 = widths.values().map(|&w| w as u32).sum();
let avg = sum as f32 / widths.len() as f32;
space_width = (avg * 0.45).max(1.0) as u16;
} else {
space_width = 250;
}
}
Some(FontWidthInfo {
widths,
default_width: 0,
@@ -1190,7 +1199,7 @@ fn extract_page_text_items(
let space_threshold = if let Some(font_info) = font_info {
let space_em = font_info.space_width as f32 * font_info.units_scale;
let threshold = space_em * 1000.0 * 0.4;
threshold.clamp(80.0, 200.0)
threshold.max(80.0)
} else {
120.0
};
@@ -1654,7 +1663,7 @@ fn extract_form_xobject_text(
let space_threshold = if let Some(fi) = font_info {
let space_em = fi.space_width as f32 * fi.units_scale;
let threshold = space_em * 1000.0 * 0.4;
threshold.clamp(80.0, 200.0)
threshold.max(80.0)
} else {
120.0
};