# PDF Denoise Remove visual noise from scanned PDF pages — salt-and-pepper speckle, random grain, and faint background haze — using real image-processing algorithms. Text pages are preserved as searchable vector content. > Canonical page: https://elysiatools.com/en/tools/pdf-denoise - **Category:** PDF Tools - **Keywords:** pdf, denoise, denoising, noise, speckle, salt and pepper, median filter, binarize, otsu, despeckle, scan, clean ## Overview Cleans noisy scanned PDF pages with a pure-JavaScript pipeline (no external binaries required) and genuine image-processing kernels. **Per-page content-aware processing (important):** - **Image pages** (scanned documents): rasterized and denoised. This is where noise removal matters. - **Text pages** (including mixed text + image): copied verbatim. Vector text, fonts, and searchability are fully preserved. - **Empty pages**: copied verbatim. If your scan carries an OCR text layer (so it reads as a "text" page) but the underlying image is still noisy, enable "Rasterize Text Pages" to force processing. **Denoise modes (all real algorithms):** - **Auto**: 3x3 median filter + isolated-speck despeckle. Balanced cleanup that preserves tone and edges — the recommended default. - **Median**: 3x3 per-channel median filter (1–3 passes). The classic remedy for salt-and-pepper / impulse noise. - **Binarize**: Otsu adaptive threshold. Collapses faint background haze into clean white and renders foreground to solid black — ideal for legibility of scanned text. **How it works (image pages):** 1. Each image page is rasterized with pdf.js 2. The chosen denoise kernel runs on the raw pixel buffer 3. The cleaned image is embedded into a new PDF ## Inputs - **PDF File** (file): Upload a PDF file - **Denoise Mode** (select): Auto: balanced median + despeckle (preserves tone). Median: best for salt-and-pepper/impulse noise. Binarize: Otsu threshold turns faint backgrounds white and text solid black. - **Strength (median passes)** (number): Number of 3x3 median filter passes (1–3). Higher = stronger noise removal but more softening. Ignored in Binarize mode. - **Rasterize Text Pages** (select): By default text pages are preserved as searchable vector content (not denoised). Enable this only for OCR'd scans whose underlying image is noisy, accepting loss of text selectability. - **Page Range** (text): Specify pages to denoise (e.g., 1-3,5,7-9). Leave blank to process all pages. ## When to use - When scanned PDF documents contain distracting salt-and-pepper noise, grain, or dark speckles that hinder readability. - When faded or low-contrast scans need to be converted into high-contrast, crisp black-and-white text. - When cleaning up scanned documents that contain a mix of noisy image pages and clean, searchable vector text pages. ## How it works - The tool parses the uploaded PDF and identifies image pages versus vector text pages. - Image pages are rasterized, and the selected denoising algorithm (Auto, Median, or Otsu Binarization) is applied directly to the pixel buffer. - Vector text pages are preserved intact to maintain searchability and font quality, unless forced rasterization is enabled. - The processed image pages and preserved text pages are compiled back into a clean, optimized PDF file. ## Use cases - Cleaning up old, grainy historical document scans to improve legibility. - Preparing scanned contracts or forms with faint backgrounds for OCR processing by binarizing them. - Removing salt-and-pepper noise from scanned textbook pages while keeping the digital text pages sharp. ## Frequently asked questions ### Will this tool make my searchable PDF text unsearchable? No, by default, vector text pages are preserved verbatim to keep them searchable. Only image-only pages are rasterized and denoised. ### What is the difference between the Auto and Binarize modes? Auto mode uses a median filter and despeckling to preserve tones, while Binarize uses Otsu thresholding to turn backgrounds pure white and text solid black. ### How do I clean a scanned PDF that already has an OCR text layer? Enable the 'Rasterize Text Pages' option to force the tool to process and denoise the underlying noisy images, though this will remove the text layer. ### Can I denoise only specific pages of my PDF? Yes, you can specify a page range (for example, '1-3, 5') to target only the pages that require cleanup. ### What does the strength setting do? It controls the number of median filter passes (from 1 to 3) in Auto and Median modes; higher values remove more noise but may soften the image. ## Related tools - [PDF Clean (PDF清理工具)](https://elysiatools.com/en/tools/pdf-clean): Remove metadata, annotations, bookmarks, and form fields from PDF files - [PDF Crop Pages](https://elysiatools.com/en/tools/pdf-crop-page): Crop PDF pages by removing margins from edges - [PDF Delete Pages](https://elysiatools.com/en/tools/pdf-delete-page): Delete specified pages from a PDF document - [PDF Header/Footer Noise Remover](https://elysiatools.com/en/tools/pdf-header-footer-noise-remover): Compare extraction with and without repeated page furniture to spot header/footer noise before using PDF text in RAG, summarization, or editing workflows - [PDF Text Extractor](https://elysiatools.com/en/tools/pdf-text-extractor): Extract text content from PDF documents with support for page selection, formatting options, and multi-language processing - [Barcode Batch Generator](https://elysiatools.com/en/tools/barcode-batch-generator): Batch generate Code 128, EAN-13, UPC-A, ITF-14, QR Code, and Data Matrix outputs from CSV or multiline text - [PDF Secure Redaction Sanitizer](https://elysiatools.com/en/tools/pdf-secure-redaction-sanitizer): Permanently remove PDF text and hidden page objects by rebuilding an image-only PDF. - [PDF Optimize Advanced](https://elysiatools.com/en/tools/pdf-optimize-advanced): Advanced PDF optimization: remove metadata, clean structure, and recompress content ## Samples - [PDF Samples](https://elysiatools.com/en/samples/pdf-samples): Generated PDF samples from tools dated 2026-02-01 to 2026-02-10 - [Markdown Slide Deck Samples](https://elysiatools.com/en/samples/md-slide-deck-to-pdf): Remark/Marp style Markdown slide decks for testing PDF export layouts - [WebRTC Real-Time Communication Samples](https://elysiatools.com/en/samples/webrtc-samples): Comprehensive WebRTC samples for peer-to-peer audio/video communication, data channels, screen sharing, and signaling server implementation - [Docker Image Tag Samples](https://elysiatools.com/en/samples/docker-image-tag): Collection of Docker image references with various registries, repositories, tags, and digests ## Related content - [PDF Archival, Accessibility, and Trust Review](https://elysiatools.com/en/hubs/pdf-archival-accessibility-trust): Clean scanned pages, add OCR, prepare PDF/A files, inspect accessibility structure, add bookmarks, and verify signatures before archival handoff.