Students
Darken faint scanned text
Adjust contrast on lecture notes or readings while comparing the original. Stop before pale characters or pencil marks disappear.
A useful change, in a few steps.
Contrast PDF.
Find a clearer balance of light and dark.
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Live preview of this page. Strong adjustments can hide faint detail or emphasize noise. Output is fixed at 200 DPI.
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Your result is ready.
Your result is ready. Download a copy, or return to adjust the settings.
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Preview stays local. Processing uploads your PDF temporarily.
PDF
How to use Contrast PDF
- 01
Choose a PDF
Open a PDF or try the sample. Previewing does not upload your document.
- 02
Adjust the settings
Choose pages and review the output options. Page numbers refer to positions in the PDF.
- 03
Process and download
Start processing to upload your file, then download the result explicitly.
Adjust PDF contrast with manual, automatic and local controls
Make faint PDF content easier to inspect with Manual contrast, Auto levels or Local contrast. Tune the sliders with a live page preview, compare the original and keep shared or individual page settings. The selected pages are saved as an image-based PDF at a fixed 200 DPI.
QUICK VIDEO TUTORIAL
How to adjust PDF contrast
Give faint pages a clearer voice.
English narration
Watch the video
Practical ways to use this tool
Educators
Adjust PDF brightness
Prepare more readable scans for handouts. Preview the active page and use individual settings when pages have different exposure.
Records & archives
Balance uneven scan contrast
Try local contrast on older records with uneven tones. Inspect details before downloading; the resulting pages are images.
Features and controls
Manual contrast: control brightness and contrast
Use Manual contrast for a direct adjustment to the whole page. Move the Contrast and Brightness offset sliders while comparing the preview.
Slider ranges and a neutral adjustment
Manual contrast is the default profile. Contrast ranges from 0.5 to 3 in steps of 0.05 and starts at 1.5. Brightness offset ranges from -100 to 100 and starts at 5. Contrast 1 with Brightness offset 0 leaves the rendered colors unchanged, though export still creates an image-based PDF.
Higher contrast increases the separation between light and dark values; brightness shifts them lighter or darker. Check fine print, pale lines and photo highlights before applying a strong adjustment. Values pushed to pure black or white lose their original tonal differences.
Auto levels: expand a faded tonal range
Let Auto levels find the page’s dark and light endpoints. Use Strength to blend the effect and Tone clipping to adjust those endpoints.
How tone clipping affects detail
Auto levels stretches page luminance across a wider range. Strength starts at 85 and ranges from 0 to 100. Tone clipping (%) starts at 0.5 and ranges from 0 to 2; the selected percentage is excluded at each end of the tonal histogram when finding the endpoints.
Increase clipping cautiously: pale pencil marks and bright photo detail can disappear. Lower Strength for a gentler blend. Blank or nearly uniform pages are left unchanged. The method adjusts luminance rather than stretching red, green and blue independently, but strong settings can still clip saturated colors.
Local contrast: bring out detail across the page
Use Local contrast for areas with uneven lighting. Balance Detail boost with Strength to reveal local differences without overemphasizing grain.
Adaptive contrast and noisy scans
Local contrast uses contrast-limited adaptive histogram equalization (CLAHE). It adjusts small areas across an 8-by-8 grid and blends neighboring areas to avoid hard tile boundaries. Detail boost ranges from 1 to 4 and starts at 2; Strength ranges from 0 to 100 and starts at 50.
This can reveal local differences when a whole-page adjustment is insufficient. It can also exaggerate paper texture, noise or color clipping. Reduce Detail boost or Strength if the preview looks harsh. For cleaning shaded paper, try Enhance Scanned PDF. No contrast profile adds OCR or recreates missing detail.
Preview one page, then choose where to apply it
The active page updates as you move the sliders. Apply to all pages is on by default; turn it off to keep different settings for individual pages.
Live preview, page ranges and reset
Only the current page is previewed on your device. Moving sliders or browsing pages does not upload the PDF or process the entire document. Use Show original to compare. The final 200-DPI rendering can differ slightly from the on-screen preview, so inspect the finished result as well.
With Apply to all pages off, changes belong to the current page, including its profile. Other pages keep their previous shared settings unless individually adjusted. Returning to a page restores its controls. Turning Apply to all pages on again copies the current page settings to every page and clears other page customizations.
Expand Pages to process to choose the output pages. A blank range includes every page; 3, 1-2 produces page 3 followed by pages 1 and 2. Settings follow original PDF page positions, not printed page numbers. Reset clears all page customizations and restores the default profile and sliders.
Download a PDF with the adjusted appearance
Selected pages are rendered at a fixed 200 DPI and assembled into a separate PDF.
Quality and what remains in the result
Start uploads the PDF and processes selected pages on our servers. Output resolution is fixed at 200 DPI; each page keeps its displayed dimensions. Pages are stored as lossless images, so the result may be larger than the source. Contrast adjustment is not a compression tool.
The new PDF contains page images. Selectable text, links, forms and other interactive elements are not retained. It does not add OCR. Keep the original, inspect the finished preview and use PDF OCR afterward if you need searchable text. Your original file stays unchanged.
Review your finished PDF
Preview the result before downloading and sharing it.
Preview, download and revise
Select Start when the settings are ready. On the result screen, Preview opens the generated PDF and Download saves a separate copy. Back returns to the current workspace; Start over clears it for a new file. Review small text, page edges and page order in the finished copy. A new PDF does not preserve the validity of an existing digital signature.
Supported files & processing
- Input
- Output
Open one PDF up to 50 MB and 200 pages. Additional output, memory and processing limits can apply to complex documents.
Processing uses our servers. Source files, temporary files and results are deleted from our servers within 30 minutes after processing finishes. We do not share document contents with third parties or use them to train AI models.
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FAQ
Good to know.
A few answers before you get started.
Server processingCan I improve PDF readability without losing faint details?
Use the live preview and compare with the original while increasing contrast gradually. Manual, Auto levels and Local contrast suit different scans. Strong adjustments can hide pale marks or amplify noise; contrast processing cannot reconstruct details missing from the scan.
When should I use Manual contrast?
Manual contrast is the default profile. Contrast ranges from 0.5 to 3 in steps of 0.05 and starts at 1.5. Brightness offset ranges from -100 to 100 and starts at 5. Contrast 1 with Brightness offset 0 leaves the rendered colors unchanged, though export still creates an image-based PDF.
What does Auto levels change?
Auto levels stretches page luminance across a wider range. Strength starts at 85 and ranges from 0 to 100. Tone clipping (%) starts at 0.5 and ranges from 0 to 2; the selected percentage is excluded at each end of the tonal histogram when finding the endpoints.
When is Local contrast useful?
Local contrast uses contrast-limited adaptive histogram equalization (CLAHE). It adjusts small areas across an 8-by-8 grid and blends neighboring areas to avoid hard tile boundaries. Detail boost ranges from 1 to 4 and starts at 2; Strength ranges from 0 to 100 and starts at 50.
Can I use a different profile on each page?
Yes. Changes update the active page preview. Apply to all pages starts enabled; turn it off to store different profiles and slider values for individual pages. Check another page before exporting, since paper and ink can vary across a document.
Will the output keep selectable text?
This tool saves the adjusted pages as images in a new PDF at 200 DPI. Existing text becomes part of those images. It does not create a new searchable text layer or restore detail missing from the source. Use PDF OCR afterward if you need recognized text.
What are the file and page limits?
Open one PDF up to 50 MB and 200 source pages. Protected files need an unlocked copy unless this tool explicitly offers password entry. Large or complex pages can require more memory or reach processing limits even when the file is within these limits.
Where is my document processed?
This tool uses our servers for processing. Your original file is not overwritten; the result is a separate download. Preview and review the result where available, and download the copy you need before starting over.
