A paralegal produces a 60-page case file from scanned documents at 300 DPI. The resulting PDF is 85MB. Their email system caps attachments at 10MB. Standard PDF compression brings it down to 70MB. Not enough. The file is enormous because every scanned page carries far more image data than any screen or email client will ever render. At 300 DPI, each page image is three times denser than a typical monitor can display.
This is the specific problem downsampling solves. Rather than squeezing the same data through compression, it physically reduces the pixel count of embedded images to a target DPI. A 300 DPI scan becomes a 150 DPI version with the same visible dimensions but half the resolution and a fraction of the file size. Text and vector elements are untouched; they are resolution-independent and remain perfectly sharp. Only the raster images get smaller. This tool does the entire process in the browser. Nothing is uploaded to any server.
How It Works
- Upload your PDF by dragging it onto the upload area or clicking to browse. The tool detects all embedded images in the document and shows the current page count and file size. A pre-processing size estimate displays the projected output size before you commit to any settings.
- Configure downsampling settings by selecting a DPI preset or entering a custom target. Preset options are Screen (96 DPI), Email (72 DPI), Web (150 DPI), and Print (200 DPI). Set JPEG quality as a percentage (default 75%) to control the compression applied during re-encoding. Choose the downsampling algorithm: Lanczos for best quality at the cost of processing time, Bilinear for a balanced result, or Nearest for fastest processing. Set which images to target: All Images, Large Images Only (above 500px), or Extra Large Only (above 1000px). Choose page scope: All Pages, Current Page, Odd Pages, or Even Pages. The Preserve text and vector quality toggle is on by default and ensures that text, fonts, and vector graphics are never touched by the image processing pass.
- Downsample and download by clicking Downsample Images. The tool processes every qualifying image, resamples it to the target DPI, re-encodes it as JPEG at the specified quality, and rebuilds the PDF with the new image data embedded. Download the reduced file immediately.
Compatibility & Support
Supported Input and Output
- Input: Any standard PDF containing embedded raster images (scanned documents, photo PDFs, exported brochures, exported presentations)
- Output: PDF with downsampled image objects re-encoded at target DPI and JPEG quality
- DPI presets: 72 (Email), 96 (Screen), 150 (Web), 200 (Print), or custom
- Downsampling algorithms: Lanczos (best quality), Bilinear (balanced), Nearest (fastest)
- Image targeting: All images, Large images (500px+), Extra Large images (1000px+)
- Page scope: All Pages, Current Page, Odd Pages, Even Pages
What Downsampling Does Not Affect
Text, fonts, and vector graphics are resolution-independent in PDF and are completely unaffected by this process. PDFs that contain only text and vector content with no embedded raster images will see no meaningful size reduction. Downsampling is specifically effective on scanned document PDFs, photography-heavy brochures, exported presentation slides with embedded photos, and any PDF where images drive the file size.
File Size Limits
All processing runs in-browser with no server upload, so no external size cap is imposed. Very large multi-page scanned documents take longer to process but complete fully. The pre-processing size estimate visible before clicking Downsample gives you a preview of the expected output size at your current settings before the full processing run.
Who Should Use This Tool?
- Students: A student scanning handwritten notes and lecture materials at 300 DPI for archive purposes can create a web-sharing copy at 150 DPI for uploading to a shared course folder, keeping both the high-res original and a compact shareable version from the same source file.
- Freelancers & Designers: A graphic designer exporting a 20-page client brochure at 300 DPI for print can generate a 150 DPI web version by downsampling the exported PDF, producing a shareable file that is 60 to 70 percent smaller without requiring a separate export from the source design files.
- Office Professionals: A paralegal compiling a scanned case file that exceeds email size limits can downsample to 96 DPI for the court's electronic review copy while keeping the 300 DPI original on file, addressing the email attachment problem without degrading the archive quality.
- Developers: A developer managing a document storage system can use this tool to generate compact screen-resolution copies of uploaded PDFs as preview versions, reducing storage costs and bandwidth without destroying the original high-resolution archival files.
Key Features
Here's what separates this tool from generic alternatives:
No Server Upload
All image resampling and PDF rebuilding runs in the browser. Scanned legal documents, medical records, and confidential reports never transfer to any external server during the process.
Pre-Processing Size Estimate
The tool shows your original file size alongside the estimated output size before processing begins. Adjust DPI and JPEG quality settings until the estimate matches your target file size, then run the actual processing once.
Targeted Image Size Filtering
Process All Images, Large Images Only (above 500px), or Extra Large Only (above 1000px). For PDFs mixing small icons with large photographs, targeting Extra Large only avoids degrading the small graphics while still shrinking the oversized images that drive file size.
Three Resampling Algorithms
Lanczos preserves the most detail during downsampling and is best for documents where image sharpness matters. Bilinear is the balanced default for most use cases. Nearest is the fastest option when speed matters more than image smoothness.
Text and Vector Preservation
The Preserve text and vector quality toggle ensures fonts, text layers, vector shapes, and diagrams are never touched during the image pass. Only raster image objects are resampled; everything else stays exactly as it was in the original.
Four Page Scope Options
Apply downsampling to All Pages, the Current Page, Odd Pages, or Even Pages. Useful when only certain sections of a document contain high-resolution images that are driving the overall file size.
Why This Tool Beats the Alternatives
- No account, email, or signup required at any point.
- No watermarks added to the output PDF.
- No server upload; scanned documents and confidential files stay in the browser throughout processing.
- Pre-processing size estimate lets you dial in the right settings before committing to the full processing run.
- Three resampling algorithms give quality-versus-speed control that most free PDF tools do not expose.
- Image size filtering (All, Large Only, Extra Large Only) targets the images that actually matter without degrading everything.
Pro Tips
- For email attachments where text readability is the priority and photos are secondary, start with 96 DPI at 75% JPEG quality and check the size estimate. If the target is still above the email server limit, drop to 72 DPI. The difference between 96 and 72 DPI is noticeable only when zoomed in close, not at normal reading scale on a screen.
- Use the Extra Large Only filter on design PDFs that contain both small UI icons and large background photographs. The icons are already small enough that downsampling them produces no meaningful size reduction and may degrade their appearance. Restricting downsampling to images above 1000px hits the large background images while leaving small elements untouched.
- Downsampling and general compression work best as a combined pass. Run this tool first to reduce image DPI and JPEG quality, then follow up with the Compress PDF tool to optimize the PDF structure and object streams as well. The two approaches address different sources of file size and together produce a smaller result than either pass alone.
Upload your PDF, check the size estimate at your target DPI, and download the reduced file in seconds. For a more general PDF size reduction that also targets non-image content, the Compress PDF tool handles the full optimization pass alongside image compression.