yoge
76f1bde56d
- how-ai-reads-math: plain-English explainer of the recognition pipeline - student-workflow: lecture-to-LaTeX workflow for students - pdf-formula-issues: troubleshooting guide for PDF extraction errors - copy-math-to-word: 3 methods for getting formulas into Word, ranked - researcher-workflow: digitizing handwritten research notes at scale Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
3.9 KiB
title, description, slug, date, tags
| title | description | slug | date | tags | |||
|---|---|---|---|---|---|---|---|
| Why Your PDF Formulas Come Out Wrong (and How to Fix It) | The most common reasons PDF formula extraction produces errors, and exactly how to fix each one | pdf-formula-issues | 2026-02-15 |
|
Why Your PDF Formulas Come Out Wrong (and How to Fix It)
PDF formula extraction should be simple — upload, get LaTeX, done. But sometimes the output looks garbled, symbols are missing, or the extractor says no formulas were found. Here's a breakdown of the most common causes and how to fix each one.
Problem 1: The PDF is a Scan
Symptoms: Symbols look correct on screen but extraction output is garbage or empty.
Why it happens: A scanned PDF is just a collection of images — there's no actual text layer. The text you see in your PDF reader is either from OCR performed at scan time (often poor quality) or from the image itself.
Fix: Run TexPixel's image-based pipeline instead. Export individual pages as PNG at 300 DPI using any PDF viewer (File → Export as Image in Preview, or Adobe Acrobat's Export PDF feature), then upload the PNG directly. Image-based recognition handles scans correctly; direct PDF text extraction does not.
Problem 2: Low-DPI Scan
Symptoms: Some symbols recognized correctly, others replaced with wrong characters or dropped entirely.
Why it happens: Below about 150 DPI, strokes in small symbols like \prime, \cdot, or subscript characters become a few pixels wide — too blurry to reliably distinguish.
Fix: Rescan at 300 DPI. Most modern flatbed scanners default to 200 DPI; bumping to 300 produces dramatically better results without significantly increasing file size. For phone scans, use a dedicated scanner app (e.g., Adobe Scan, Microsoft Lens) which applies automatic sharpening and perspective correction.
Problem 3: Password-Protected PDF
Symptoms: "No formulas found" or upload fails entirely.
Why it happens: Encrypted PDFs require a password to access their content stream. TexPixel cannot process the content of a locked file.
Fix: Remove the password protection before uploading. In Preview (Mac), open with the password, then File → Export as PDF — the exported file won't have the password. In Adobe Reader, use File → Print → Save as PDF.
Problem 4: Formulas Stored as Vector Paths
Symptoms: PDF looks perfect, but extraction returns nothing or incorrect text.
Why it happens: Some PDF generators (certain Word versions, some online LaTeX renderers) rasterize or vectorize math into paths — the formulas are essentially drawings, not characters. There's no character stream to extract.
Fix: Export the page as a high-resolution PNG (300 DPI), then upload as an image. TexPixel's visual recognition pipeline handles vector-rendered formulas well.
Problem 5: Multi-Column Layout
Symptoms: Formulas from two columns are merged or interleaved in the output.
Why it happens: PDF text streams don't always encode reading order correctly, especially in two-column academic papers.
Fix: Crop to a single column before uploading. Use any image editor to crop the page into left and right halves, then upload each separately.
Problem 6: Handwritten Annotations
Symptoms: Handwritten notes over a printed formula confuse the output.
Why it happens: TexPixel sees both the printed formula and the handwritten annotations together. It may try to recognize the annotations as part of the formula.
Fix: Crop tightly to just the printed formula, excluding any handwriting around it.
Quick Diagnostic Checklist
Before uploading a problematic PDF:
- Is it a scan or a born-digital PDF?
- If a scan, what DPI was it scanned at?
- Is it password-protected?
- Does it have a two-column layout?
- Are there handwritten annotations?
Working through this list resolves the issue 90% of the time.