Fix Blurry PDF Images After Compression
Over-compressed PDFs lose image sharpness. Here's how to find the right compression level for your document type and recover quality from an already-compressed PDF.
Blurry images in a compressed PDF happen when the JPEG re-encoding quality was set too low — either by your compression tool's "aggressive" mode or by compressing an already-compressed PDF a second time. The good news: if you still have the original, you can re-compress at a better setting. If you only have the blurry version, options are limited but not zero.
Why Compression Makes Images Blurry
PDF compression works by re-encoding embedded images at lower JPEG quality. JPEG is a lossy format — each compression introduces artefacts that blur fine details and create blocky patterns around high-contrast edges. Compressing a PDF twice is particularly destructive: the second pass introduces new artefacts on top of the first pass's degraded data, compounding the quality loss. A photo compressed to JPEG 60% quality and then compressed again to 60% doesn't result in the same file as one original compression to 36% — it's worse, because you're adding artefacts to artefacts.
The Right Compression Level for Each Document Type
Not all PDFs need the same compression approach. Text-only documents: use High compression freely — JPEG quality doesn't matter because there are no photos. Text is stored as vectors (not images) and isn't affected. Scanned documents: Medium compression is usually optimal — it achieves 50-70% reduction while keeping text sharp enough to read. Photo portfolios or product catalogues: Low compression only — preserves image fidelity while still achieving 20-35% reduction. Engineering drawings or architectural plans: use Low or no compression — fine lines and small text are critical.
If You Have the Original, Re-compress at the Right Setting
Go back to your original uncompressed PDF and re-run through FixMyPDF's compressor at a lower compression level. Download the result and zoom to 100% in a PDF viewer to check image quality — this is the actual rendered resolution. If quality is acceptable, use that version. The key principle: always compress from the original, never from a previously compressed copy. Keep the original archived and generate a compressed copy when needed.
If You Only Have the Blurry Version
Lossy JPEG compression is irreversible — you cannot recover detail that was discarded. However, for text-containing images, AI upscaling tools (Topaz Gigapixel, Adobe Photoshop Neural Filters) can reconstruct some sharpness by inference. Extract the blurry images from the PDF (most PDF viewers let you right-click → save image), upscale with an AI tool, then re-insert using FixMyPDF's image insertion tool. This won't recover original quality but produces a significantly better result than the blurry version.
Preventing Quality Loss Before You Compress
Before compressing a PDF, check what it contains using FixMyPDF's PDF Inspector to see embedded image resolutions and sizes. If images are already at 72-96 DPI (screen resolution), further compression will degrade quality noticeably — the images are already at minimum useful resolution. Only compress PDFs where images are at 150 DPI or higher, where there's genuine reduction potential. For scanned PDFs, scan at 200 DPI (not 300) if file size is a concern — this gives 33% smaller files from the start without needing aggressive compression.
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