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Reduce file size without losing quality.
Scanned documents often contain skew, speckles, low contrast, and uneven lighting – all of which confuse OCR engines. Our AI‑powered enhancement prepares your scan for perfect text recognition: auto‑deskew pages, remove dust spots, normalise contrast, and upscale to 300 DPI. The result is a clean, high‑contrast image that dramatically improves OCR accuracy. Whether you are digitising books, receipts, or legal documents, pre‑processing your scan is the most important step for reliable OCR. No software installation required.
Did you know? OCR accuracy on raw 150 DPI scans can be as low as 60% for small fonts. After our enhancement (deskew + despeckle + upscale to 300 DPI), accuracy often exceeds 95% on the same document.
OCR engines are highly sensitive to image quality. These defects cause recognition errors:
Even 2‑3 degrees of rotation confuses baseline detection, turning "rn" into "m" and "ll" into "u".
Random dots are misread as punctuation or part of letters, creating extra characters.
Light grey text on a grey background yields many uncertainties – the engine guesses incorrectly.
At 150 DPI, letter shapes are pixelated; the engine cannot distinguish similar characters (O, 0, Q).
Bonus issue – background bleed‑through: Text from the reverse side of a page adds ghost letters that OCR may incorrectly recognise. Background flattening removes this.
Upload your scanned PDF – The tool analyses page skew, noise, contrast, and current DPI.
Enable OCR‑prep mode – Despeckle, deskew, contrast equalisation, and upscale to 300 DPI are applied automatically.
Preview the enhanced document – Check that text is dark, background clean, and lines straight.
Download the enhanced PDF – Then run our OCR tool to extract searchable, editable text.
Pro Tip: For maximum OCR accuracy, enable "Text‑only sharpening" after upscaling. This enhances letter edges without affecting photos. Use our "OCR Optimised" preset – it applies ideal settings for Tesseract, Adobe, and ABBYY engines.
Our OCR‑prep mode combines all four in one click. You can adjust individual strengths using the advanced panel.
We tested a 150 DPI scan of a typewritten letter (font size 10). Raw OCR accuracy was 63%. After our enhancement pipeline, accuracy rose to 97%. Common errors fixed: "rn" → "m" (baseline skew), "0" → "O" (low contrast), and extra punctuation (speckles). The same improvement applies to receipts, books, and legal documents.
Trusted by professionals: A large accounting firm uses our OCR‑prep tool before processing 10,000+ thermal receipts monthly. Accuracy increased from 71% to 96%, saving hundreds of hours of manual correction.
Our enhanced PDFs work seamlessly with Tesseract, Adobe Acrobat OCR, ABBYY FineReader, Google Cloud Vision OCR, and any other engine. The output is a standard PDF with high‑quality images and an optional scaled‑up resolution. You can then run OCR using your preferred tool – or use our own free online OCR tool.
Tip: If you plan to use Tesseract, enable "Binarisation" mode in our tool – it converts the image to pure black and white, which Tesseract prefers.
⚡ Need to adjust or standardise DPI without changing pixels?
Use our dedicated PDF DPI Changer to view, adjust, or unify the DPI metadata of embedded images. Perfect for pre‑press compliance, print workflow validation, and preparing files for commercial printing without altering visual quality.
OCR engines work best on clean, high‑contrast, straight text. Dust speckles, skew, low contrast, and background noise cause misrecognitions. Enhancing your scan first can boost OCR accuracy by up to 40%, especially for small fonts or poor‑quality originals.
The four critical enhancements are: deskewing (straightening crooked lines), despeckling (removing dust spots), contrast equalisation (darkening text, whitening background), and resolution upscaling to 300 DPI. Our OCR‑prep mode applies all four automatically.
Yes. Most scanned text is at 150‑200 DPI. OCR engines expect 300 DPI for optimal character recognition. Upscaling to 300 DPI smooths jagged edges and provides more pixels per character, reducing confusion (e.g., "rn" vs "m").
Upscaling to 300 DPI will increase file size (typically 2‑3x). However, you can compress the final PDF after OCR. Our workflow suggests: enhance → OCR → compress. Compression after OCR does not affect the text layer.
Yes, but the existing text layer may become misaligned after image enhancement. For best results, enhance the original scan before running OCR. If you already have a searchable PDF, you can extract the images, enhance them, then re‑OCR.
After enhancement, open the PDF and look for: uniformly white background, solid black text, straight baselines, and no speckles. Test a sample page with our online OCR tool – if a short paragraph is recognised with 99% accuracy, the rest will be fine.
Yes. All uploads are encrypted with TLS 1.3 and automatically deleted within 24 hours. We never use your documents for training. An offline desktop version is also available for organisations with strict data policies.
Yes, the tool is fully responsive and works on iOS and Android. Upload from cloud storage or camera roll. Processing runs in the cloud, so your device does not need high processing power.
Upload your scanned PDF, apply our OCR‑prep enhancement, and then run OCR for near‑perfect text recognition.
Enhancing a PDF improves visual clarity by adjusting resolution, sharpening text edges, and increasing contrast between foreground and background elements. This process is particularly useful for scanned documents, blurry text, or faded paperwork.
Several factors may reduce the readability of a PDF document. Low-resolution scanning, aggressive compression, improper export settings, and camera-captured documents can all introduce blur or reduce contrast.
Modern PDF enhancement tools apply multiple processing techniques to improve readability.
PDF enhancement algorithms work by analyzing pixel density and grayscale distribution. Contrast adjustment increases the difference between text and background while sharpening filters reconstruct blurred edges. When combined with OCR preparation, enhancement dramatically improves machine readability.
Explore the full collection of tools in the PDF Enhancement Guide.