Backlight Subtraction Paper Reproduction Method

This is about the development of this reproduction method, detailing issues and proposals for solutions.

1. Light variation - Best results are obtained with a uniform light intensity across the whole page.
   1. Recommendation - Photograph an uniformly colored page to record the intensity distribution of light. Then use digital background equalization.
2. Side to imagine - Test if it's the same if a paper gets backlight from side A or side B.
3. Writing on both sides - If writing exists on both sides of the paper, like in manuscripts, it is necessary to take two frontlight images in order to remove the traces of ink. It might also be neccessary to do also two backlight images. Experiment.
4. Mechanical mouvement - Even minimal movments of the paper during photographing will result in lessening the quality of the paper structure image. Attention at the movement of paper due to the heat emitted by the light source.
5. Optical distortion - Another distortions source might be introduced by the lenses of the camera.
6. Registration - Registration might be difficult if there are not enough landmarks on the two images to register. Four landmarks are not sufficient, distortions are non-linear.
7. Digital distortion - During digital image processing - for regitsration for ex. - images are also distorted. Find out if it is significative for the need of paper structure reproduction for paper expertise.

-- VladAtanasiu - 18 Dec 2006