Detecting PDF Headers and Footers Without Relying on Page Margins

TLDR

Position-only Y-coordinate thresholds ($Y < 8\%$ or $Y > 92\%$) fail on non-standard PDF layouts (full-bleed titles, large figure captions near margins). Combining three structural signals, relative font size ($< 0.78 \times \text{body average}$), colored background bands (filledRects), and regex pattern matching (Page 1 of 5), yields reliable header/footer classification. Resetting columnIndex = -1 on reclassified regions ensures headers render full-width outside multi-column grid containers.

Detection Signal	Technical Implementation	Detection Purpose
Relative Font Size	avgFontPt < bodyFontPt * 0.78	Identifies small-print running headers
Background Color Band	filledRect.width > viewportWidth * 0.6	Detects background header banner fills
Regex Pattern Match	/\bpage\s+\d+	\b\d+\s+of\s+\d+/i

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Technical implementation architecture

// Header and Footer Classification Post-Pass
export function classifyHeadersAndFooters(regions, bodyFontPt, viewportHeight, viewportWidth, filledRects) {
  for (const region of regions) {
    const isTopZone = region.yCenter < viewportHeight * 0.15;
    const isBottomZone = region.yCenter > viewportHeight * 0.85;
if (!isTopZone && !isBottomZone) continue;
const regionText = region.text.trim();     const nonSpaceCount = regionText.replace(/\s/g, '').length;
// Signal 1: Relative font size     const isSmallFont = region.avgFontPt < bodyFontPt * 0.78;
// Signal 2: Colored background band overlap     const inColoredBand = filledRects.some(rect =>       rect.w > viewportWidth * 0.6 &&       rect.y <= region.bbox.y + 4 &&       rect.y + rect.h >= (region.bbox.y + region.bbox.h) - 4     );
// Signal 3: Pagination or metadata regex pattern     const isPatternMatch = /\bpage\s+\d+|\bpg\.?\s*\d+|\b\d+\s+of\s+\d+|\b\d{4}-\d{2}-\d{2}/i.test(regionText);
// Filter out single-character stray glyphs unless matching page numbers     if (nonSpaceCount < 2 && !isPatternMatch) continue;
if (isSmallFont || inColoredBand || isPatternMatch) {       region.type = isTopZone ? 'HEADER' : 'FOOTER';       // CRITICAL: Reset columnIndex = -1 so header renders full-width outside column grid       region.columnIndex = -1;     }   } }

Rule of thumb: Combine relative font sizes, background fill banners, and regex patterns to detect headers/footers, always resetting columnIndex = -1 to prevent grid containment bugs.