Scanning from Book - Gradient Removal

Question

This sample image:

is warped on the left side.

I don't want to dewarp, but just to remove shadow gradient (caused by book's spine). I guess gradient can be calculated from upper part of the image and that information can be used for reconstruction.

First I thought to apply some layer transformation in Photoshop. I took upper part with clear gradient and scaled it vertically to cover whole image in new layer. Then I did layer difference:

but while upper part is acceptably reconstructed, colored part is not.

Does anyone have an idea how to approach this in Photoshop, or Python/SciPy/OpenCV, or Matlab?

try applying a saturation filter with same mask in photoshop — geometrikal, Mar 06 '13 at 09:12
Hi geometrikal ;) Can you post it as answer and paste result screenshot? Thanks — zetah, Mar 06 '13 at 10:55

score 8 · Accepted Answer · answered Mar 09 '13 at 05:39

8

The simplest approach would be to divide the gradient rather than subtract it. Here's what the result looks like:

Gradient Removal

answered Mar 09 '13 at 05:39

datageist

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This is really cool! How did you extract the gradient? – Phonon Mar 09 '13 at 05:42
Oh, same way as the OP did (I think). Took the top section and scaled it vertically. – datageist Mar 09 '13 at 05:44
Cool, I suspected so. = ) – Phonon Mar 09 '13 at 05:47
Thanks, it works great. From the layer operation blend naming, I assume you use Gimp ;) – zetah Mar 09 '13 at 11:57
I actually used PS (CS6), but was thinking more about math than blend modes :) – datageist Mar 09 '13 at 13:04

Scanning from Book - Gradient Removal

1 Answers1