Algorithms for: printer checker

I want to make a program for checking the printed paper for errors.

PDF File: please refer to the second page, top right picture

As you see, that system could identify the errors made by printer. I want to know how was开发者_如何学JAVA it achieved. What are existing documents about this? Or any ideas you have? Thank you

---

This can be very easy or very difficult. if your images are black white and your scan is quite precise you can try with a simple subtraction between the images (scanned and pattern) if your scan will read the image with a possible deformation or translation the you will need first an image registration algorithm. if your scan present background noise you will have some trouble with the subtraction and then it turns very difficult. may be some image samples can help to suggest you a more specific algorithm.

---

I think you need to some how compare two images in a way that is robust to deformation. As mentioned before, substracting the two images can be a first step. Another more sophisticated way can be to use distance transform (or chamfering based methods for template matching) to compare how similar the two images are in the presence of some deformation. More sophisticated solutions can use methods like shape contexts.