Optical detection method during print finishing

1. An optical control method for use in print finishing, comprising:

guiding a planar printed product along a conveying path past at least one optical sensor;

capturing an electronic image by use of the at least one optical sensor, wherein the electronic image represents at least one region of the printed product;

extracting orientation information from the electronic image using a frequency transformation of the electronic image, said orientation information reflective of an orientation of the printed product;

comparing the orientation information of the printed product from the electronic image with reference orientation information based on a first correlation, wherein the reference orientation information is based on a frequency transformation of a reference image; and

generating at least one signal that reflects a result of the comparison,

wherein the at least one signal comprises a first signal, which initiates a special treatment of the printed product on which the electronic image is based, if a correlation value of the first correlation falls below a first threshold value,

wherein a rotation angle between the controlled printed product and the reference printed product together with direction information is calculated on the basis of the orientation information and the reference orientation information, and

wherein the electronic image is rotated back by the rotating angle in such a way that the printed product imaged thereon has the same orientation as the reference printed product.

2. The control method as claimed in claim 1 , wherein extracting the orientation information comprises:

generating a frequency transformation of the electronic image;

performing absolute value formation on the basis of the frequency transformation; and

generating the orientation information by use of a polar transformation based on the absolute value formation.

3. The control method as claimed in claim 1 wherein the reference orientation information is extracted from a reference image of a reference printed product, and wherein extracting the reference orientation information comprises:

generating a frequency transformation of the reference image;

performing reference absolute value formation on the basis of the frequency transformation; and

generating the reference orientation information by use of a polar transformation based on the reference absolute value formation.

4. The control method as claimed in claim 1 ,

wherein the rotated-back electronic image is compared with the reference image on the basis of a second correlation, and

wherein the at least one signal comprises a second signal, which initiates a special treatment of the printed product on which the electronic image is based, if a correlation value of the second correlation falls below a second threshold value.

5. The control method as claimed in claim 4 , wherein the second correlation is performed when the first correlation result is greater than or equal to the first threshold value.

6. The control method of claim 1 , wherein at least extracting the orientation information takes place in real time, within an operating cycle time.

7. The control method of claim 1 , wherein extracting the orientation information takes place on the basis of geometry data of the captured printed product.

8. The control method of claim 1 , wherein extracting the orientation information takes place on the basis of at least one image of the captured printed product.

9. The control method of claim 1 , further comprising compensating for sensor-dictated errors in the electronic image.

10. The control method of claim 1 , wherein the electronic image is a corrected image.

11. An apparatus for carrying out an optical control method, the apparatus comprising:

at least one optical sensor for capturing electronic images of printed products;

a conveyor for transporting the printed products past the at least one optical sensor; and

an image processing system configured to (1) extract orientation information of a printed product from the electronic image using a frequency transformation of the electronic image and (2) compare the extracted orientation information with reference orientation information based on a first correlation, which reference orientation information reflects a frequency transformation of a reference image, and (3) generate at least one signal that reflects a result of the comparison,

wherein the at least one signal comprises a first signal, which initiates a special treatment of the printed product on which the electronic image is based, if a correlation value of the first correlation falls below a first threshold value,

wherein a rotation angle between the controlled printed product and the reference printed product together with direction information is calculated on the basis of the orientation information and the reference orientation information, and

wherein the electronic image is rotated back by the rotating angle in such a way that the printed product imaged thereon has the same orientation as the reference printed product.

12. The apparatus as claimed in claim 11 , wherein the optical sensor, when capturing the electronic images, is at a distance from the printed products to be controlled, wherein the distance corresponds at least approximately to a diagonal of a printed product.

13. The apparatus as claimed in claim 11 , wherein a recording direction of the optical sensor is arranged at a free angle with respect to the printed products to be captured.

14. The apparatus of claim 11 , wherein the apparatus has a light source in the form of a reflected light source of a transmitted light source for enhancing the contrast of the electronic images.

15. The apparatus of claim 11 , wherein the image processing system is further configured to:

generate a frequency transformation of the electronic image;

perform absolute value formation on the basis of the frequency transformation; and

generate the orientation information by use of a polar transformation based on the absolute value formation.

16. The apparatus of claim 11 , the image processing system is further configured to extract reference orientation information from the reference image of a reference printed product, comprising:

generate a frequency transformation of the reference image;

perform reference absolute value formation on the basis of the frequency transformation; and

generate the reference orientation information by use of a polar transformation based on the reference absolute value formation.