Remove shadows from a scanned PDF

How to remove shadows from a scanned 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. Look at the edge of the page where the shadow was.
4. If shading remains, choose Full. If the paper still looks grey rather than white, raise Also whiten paper, then press Apply new settings.
5. Download the new PDF. The original is left untouched.

How it works

The page is divided into a grid of small cells. In each cell, the brightest fifth of the pixels is taken as the local paper level, and the grid is smoothed twice so the estimate is a gentle surface rather than a map of the text. Each pixel is then multiplied by the ratio of the page-wide paper level to its local paper level.

The result is paper that sits at one even level across the page. It is not whitened, so a cream page stays cream and a grey page stays grey; that is a separate choice, and the Also whiten paper slider makes it if you want it.

Which shadows it can handle

• Smooth shadows and gradients, such as a phone casting its own shade or a bright centre with dark corners.
• Book-spine darkening, where the paper falls away into shadow near the gutter.
• Limit: the lighting estimate treats anything much darker than the paper as content rather than shadow. Shadows that darken the paper by about a third or less are corrected; deeper ones are only partly corrected.
• Sharp-edged shadows, such as a finger, a fold or the edge of another sheet, change too quickly for a smooth estimate and are only softened.

Large dark areas are protected

A filled table header, a stamp or a photograph is a large dark area, but it is not lighting. The estimate ignores anything below about 65% of the paper level, so these are not "corrected" into white. If a very large dark area still shifts, lower the strength.

Shadow removal and the rest of the cleanup

• To whiten the paper as well, use the second slider here, or whiten PDF background on its own.
• To clear dust and specks, use remove noise.
• To do all of it and darken the ink as well, use clean a scanned PDF.

If you can, rescan

Software repairs shadows after the fact. A better capture avoids them: diffuse light from the side instead of a lamp overhead, a flat page, and the camera parallel to the paper. For a book, a flatbed scanner pressed gently closed gives much more even lighting than a phone.