DocVerify Pro › Remove a shadow from a document photo
Removing the shadow from a photo of a document
You lean over the page to line up the shot, and the light you are working under is behind you. The shadow is not bad luck — it is geometry, and it happens to everybody.
The short answer. Move the page so the light comes from in front of you rather than behind, or use a window instead of a ceiling light. If the photo is already taken, the shadow can be removed by rebuilding the tone across the page — but only if the shadowed area still holds detail.
Why the shadow lands exactly on the page
Indoor light almost always comes from above and slightly behind where you stand. To photograph a page on a table you lean over it, putting your head and shoulders between the lamp and the paper. The darkest part of the shadow falls where you are looking — which is the middle of the document.
Preventing it, which is far easier than fixing it
- Use a window, not the ceiling light. Put the page on a table beside a window with the light arriving side-on.
- Stand so the light is in front of you. If you can see your own shadow on the page, turn around.
- Do not use flash. Flash replaces a soft shadow with a hard white blowout over whatever it hits, and a blown-out area has no detail left to recover.
- Shoot from directly above. A tilted camera puts one edge of the page further from the light than the other, which adds a gradient on top of the shadow.
Removing one that is already there
A shadow is a smooth change in brightness across the page. The text underneath it is still there — just darker. Correcting it means measuring the paper's brightness in each region and lifting each region to the same white, so the paper reads uniformly white and the ink reads uniformly black.
What cannot be recovered is a region that clipped. If part of the page went fully black, or the flash blew part of it to pure white, there is nothing left in those pixels to lift. That part has to be rephotographed.
Beware tools that "fix" this by thresholding. Forcing every pixel to either black or white makes a shadow vanish instantly — and takes the periods, commas and thin accents with it, because those are grey at the edges. The page looks clean and a date reads wrong.
Even out the lighting across the whole page
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