Brighten a PDF

How to brighten a PDF

1. Pick a strength above. Standard is selected to begin with.
2. Choose your PDF, or drop it on the page. It is processed in your browser and never uploaded.
3. Drag the slider to compare the original with the result, and use Previous and Next to check other pages.
4. If it is not right, change the strength or move the Brightness, Background, Contrast or Text darkness sliders, then press Apply new settings.
5. Download the new PDF. The original is left untouched.

PDF brightness versus contrast

Brightness adds or subtracts tone across the page. Contrast separates the ink from the paper. They are easy to confuse, and picking the wrong one is the usual reason a scan gets worse instead of better.

If the page looks grey and heavy, brighten it. If the text looks faint, the control you want is contrast: see the PDF contrast enhancer, or darken the text directly. Raising brightness alone on faint text makes the text fainter.

What brightening does here

• Brightness lifts or lowers the mid-tones with a curve that leaves pure black and pure white alone, so it cannot clip the ink or the paper.
• Background pushes the paper towards white. It uses a paper level measured across the page rather than one global value, so a shadowed corner is corrected against its own surroundings.
• The white point is never allowed to fall onto the ink itself, which is what stops over-eager whitening from erasing faint text.
• Contrast and Text darkness are kept low in the brighten strengths so the page does not turn harsh. Raise them if the ink looks weak afterwards.

The four strengths

• Slight — a small lift for pages that are just a little dull.
• Standard — lifts mid-tones and whitens grey paper. A good first try.
• Strong — for dark or underexposed scans. It can wash out light pencil and shading, so check the result.
• Whiten paper — cleans the paper to white without lifting the mid-tones, for scans whose only problem is a grey or cream background. For whitening that leaves every dark pixel untouched, see whiten PDF background.
• Move any slider and the strength shows as Custom. Your numbers are used exactly as set.

When brightening helps

• Scans with a grey, cream or yellow paper cast.
• Underexposed phone photos of documents, where the whole page sits too dark.
• Dark photocopies where the mid-tones have clogged.
• Pages you are about to print, where a cleaner white background leaves less tone to be printed.

When it will not help

• The text itself is faint. Use contrast or darkening instead.
• The page is already white. There is little to lift, and a strong setting would only wash out detail.
• The scan is blurry or low resolution. Brightness changes tone, not sharpness.