Tips for Getting Better PDF Scans
Most scanned PDFs are either too large (because the scanner used 600 DPI when 300 DPI would have been enough), too blurry (because the phone camera wasn't held steady, or the document wasn't flat), or not searchable (because no OCR was applied after scanning). All three problems are preventable. Getting a good scanned PDF comes down to the right scanner settings for the content type, proper document preparation before scanning, and the right post-processing steps. Whether you're using a flatbed scanner, a document scanner, or your smartphone camera as a scanner, the same principles apply. This guide covers every step from document preparation to final output.
Choose the Right Scanner Settings for Your Content
Resolution (DPI) and colour mode are the two most impactful scanner settings. For text-only documents (letters, contracts, forms), 300 DPI black-and-white or greyscale gives clean, sharp results at a manageable file size. For documents with photographs or colour graphics, 300 DPI colour. For archival scanning of old or fragile documents where maximum detail is important, 600 DPI colour. Avoid 72 DPI or 96 DPI — these are screen resolutions and produce blurry printed scans. Avoid anything above 600 DPI for standard documents — you get a massive file size increase with barely any visible quality gain. Set your scanner software to save as PDF directly rather than as TIFF or BMP if possible, since scanner software typically applies better compression when saving to PDF.
- 1For text documents: set 300 DPI, black-and-white or greyscale mode.
- 2For colour documents or photos: set 300 DPI, colour mode.
- 3For archival scanning: set 600 DPI, colour mode.
- 4Enable automatic page detection and deskew in your scanner software if available.
Prepare Documents Before Scanning
The quality of your scan is largely determined before you even press the scan button. Crumpled, folded, or skewed pages produce scans that are hard to read and that OCR processes poorly. Spend a minute preparing documents properly and you'll save much more time in post-processing. Flatten pages before scanning — especially book pages, which curve at the spine. Use a ruler or a flat object to press the page gently against the glass. Remove staples, paperclips, and binding before feeding sheets through an automatic document feeder. Clean the scanner glass periodically — smudges and dust appear as streaks across every scanned page. Ensure adequate, even lighting for phone scanning to avoid shadows.
Improve Scan Quality with Image Processing
Even good scans benefit from a few post-processing steps before converting to final PDF. Deskew (auto-straightening slightly rotated pages) makes documents look professional and improves OCR accuracy significantly — a 2° rotation can drop OCR accuracy by 5–10%. Contrast enhancement makes light grey text sharper and improves readability for faded documents. For phone-scanned documents, Microsoft Lens (free), Apple's Notes scanner, and Adobe Scan all automatically apply deskew, perspective correction, and contrast enhancement before saving. For flatbed scanner output, use GIMP (free) or your scanner's bundled software to apply 'despeckle', 'deskew', and 'sharpen' filters before assembling into PDF.
- 1After scanning, review each page image for skew, shadows, and contrast issues.
- 2Apply deskew to straighten any rotated pages using your scanner software or an image editor.
- 3Increase contrast for faded documents: aim for clean black text on white background.
- 4Assemble the corrected images into PDF using lazy-pdf.com/image-to-pdf.
Always Apply OCR to Make Scans Searchable
A scanned PDF without OCR is just a collection of images — it can't be searched, copied from, read by screen readers, or indexed by search engines. Running OCR takes a few seconds per page and transforms the document from a visual artifact into a fully functional document. LazyPDF's OCR tool supports over 100 languages and adds a transparent searchable text layer over your original images, preserving the visual appearance exactly while making all text accessible. After scanning any document, running OCR should be as automatic as saving the file — make it a fixed step in your scanning workflow.
Frequently Asked Questions
Should I use a flatbed scanner or my phone for document scanning?
Flatbed scanners produce consistently better quality for standard documents — better sharpness, no perspective distortion, no shadows, and more predictable results. A mid-range flatbed scanner at 300 DPI outperforms smartphone cameras for text documents. For occasional scanning or when portability matters, smartphone scanner apps (Microsoft Lens, Apple Notes, Adobe Scan) are excellent and apply automatic image correction. For high-volume document scanning, a sheet-fed document scanner like the Fujitsu ScanSnap is far faster than a flatbed.
My scanned PDFs are huge — how do I make them smaller without losing readability?
Scanned PDFs are large because each page is a high-resolution image. Compression is very effective here: running a 300 DPI scanned PDF through LazyPDF's compress tool at 'Ebook' quality (which resamples to 150 DPI) typically reduces file size by 60–75% with no visible loss of readability at normal zoom levels. If the documents are text-only with no photographs, you can use 'Screen' quality (72 DPI) — text remains readable even at the lower resolution because character shapes are recognisable.
Why do my phone scans look fine in the scanning app but blurry after saving to PDF?
Many phone scanner apps display a processed preview that looks sharp, but save the actual file at a lower resolution. Check your app's settings for output quality or resolution — most have an option for 'High' or 'Best' quality. Also check if your phone is compressing the image when saving to the gallery before importing to the scanning app. For best results, scan directly in the app and export directly to PDF without saving to the photo library as an intermediate step.