Position information input apparatus and method

• US 6,963,331 B1
• Filed: 03/14/2000
• Issued: 11/08/2005
• Est. Priority Date: 03/17/1999
• Status: Expired due to Fees

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Tanaka, Atsushi, Kobayashi, Katsuyuki, Kobayashi, Kiwamu, Hasegawa, Masahide, Kanashiki, Masaaki, Yoshimura, Yuichiro
• Primary Examiner(s): Wu, Xiao
• Assistant Examiner(s): Nguyen, Kevin M.
• Application Number:
  US09/525,021
• Time in Patent Office: 2,065 Days
• Field of Search: 345/157, 345/156, 345179-183, 345/158, 345/169, 353/122, 348/207, 348/88
• US Class Current: 345/158
• CPC Class Codes: G06F 3/0386 for light pen
• CPC Class Codes: G06F 3/0425 using a single imaging device like a video camera for tracking the absolute position of a single or a plurality of objects with respect to an imaged reference surface, e.g. video camera imaging a display or a projection screen, a table or a wall surface, on which a computer generated image is displayed or projected tracking a projected light spot to determine a position on a display surface G06F3/0386

Abstract

The invention aims to provide a coordinate input apparatus having high detection reliability and high efficiency and to control the influence of ambient light using a simple structure. The apparatus detects a light spot flashing on and off in a predetermined cycle and incident at a desired position on a coordinate input screen, and includes a detection device having photoelectric conversion elements corresponding to N pixels for detecting a light spot coordinate. The difference between signals from photoelectric elements in light emission state and in light non-emission state at each N pixel is found, and the smaller of the difference signals of the m-th pixel having the maximum difference signal is set as a threshold value. Effective pixels are identified based on the threshold value, and the coordinate is calculated by using the difference data of the selected effective pixels.

Claims

1. An apparatus for outputting position information corresponding to light having a cyclically varying intensity, said apparatus comprising:

a detection device that receives the light, said detection device comprising a plurality of photoelectric conversion elements, arranged in a predetermined physical array;

difference signal generating means for generating, for each photoelectric conversion element, a difference signal corresponding to a difference between an output of the photoelectric conversion element when the light cycle is at a first point and an output of the photoelectric conversion element when the light cycle is at a second point, the first point being at a higher intensity than the second point;

threshold setting means for setting a threshold value on the basis of a level of said difference signal obtained from each photoelectric conversion element;

selection means for selecting effective photoelectric conversion elements by comparing said threshold value with the difference signal generated by said difference signal generating means; and

output means for outputting the difference signals corresponding to the selected effective photoelectric conversion elements.

2. An apparatus according to claim 1, wherein said threshold setting means sets the threshold value based on the difference signals corresponding to two photoelectric conversion elements equally spaced from the photoelectric conversion element having the largest difference signal.

3. An apparatus according to claim 1, wherein said threshold setting means sets the threshold value at the difference signal corresponding to the greater difference signal of the two photoelectric conversion elements equally spaced from the photoelectric conversion element having the largest difference signal.

4. An apparatus according to claim 1, wherein said threshold setting means sets the threshold value at the difference signal corresponding to the smaller difference signal of the two photoelectric conversion elements equally spaced from the photoelectric conversion element having the largest difference signal.

5. An apparatus according to claim 1, further comprising:

difference signal detecting means for detecting the photoelectric conversion element having the largest difference signal,

wherein said threshold setting means sets the threshold value based on the difference signals of a predetermined number of photoelectric conversion elements adjacent to the photoelectric conversion element having the largest difference signal.

6. An apparatus according to claim 1, further comprising:

pixel calculation means for calculating which photoelectric conversion element the light is incident on based on the difference signals outputted by the effective photoelectric conversion elements.

7. An apparatus according to claim 1, wherein said pixel calculation means calculates a centroid pixel number of a selected effective signal, further comprising position calculation means for calculating a position coordinate of a designation device based on an output result of said pixel calculation means.

8. An apparatus according to claim 1, further comprising;

storage means for storing an output result of said pixel calculation means, which is obtained at the light of a predetermined position on the screen, and information on said predetermined position.

9. An apparatus according to claim 1, further comprising:

first integration means for integrating the output of the photoelectric conversion element when the light cycle is at a first point;

second integration means for integrating the output of the photoelectric conversion element when the light cycle is at a second point; and

difference signal generating means for generating, for each photoelectric conversion element, a difference signal between the integrated output signal of when the light cycle is at the first point and the integrated output signal of when the light cycle is at the second point.

10. An apparatus according to claim 1, wherein the light comprises a light-emitting element that projects a light spot onto the screen surface.

11. An apparatus according to claim 1, wherein the light comprises a light-emitting element positioned adjacent to the screen surface.

12. An apparatus according to claim 1, wherein said detection means receives light diffused through the screen surface from the light.

13. An apparatus according to claim 1, further comprising a display device.

14. An apparatus for outputting position information corresponding to light having a cyclically varying intensity, said apparatus comprising:

a detection device that receives the light, said detection device comprising a plurality of photoelectric conversion elements, arranged in a predetermined physical array;

difference signal generating means for generating, for each photoelectric conversion element, a difference signal corresponding to a difference between an output of the photoelectric conversion element when the light cycle is at a first point and an output of the photoelectric conversion element when the light cycle is at a second point, the first point being at a higher intensity than the second point;

first threshold setting means for setting a first threshold value on the basis of a mean value of output of said difference signal obtained from each photoelectric conversion element;

second threshold setting means for setting a second threshold value to either of the difference signals outputted by a photoelectric conversion element having the largest difference signal and two photoelectric conversion elements, which are equally spaced by the predetermined number of pixels from the photoelectric conversion element having the largest difference signal;

selection means for selecting effective photoelectric conversion elements by comparing said first threshold value and said second threshold value with the difference signal generated by said difference signal generating means; and

output means for outputting the difference signal obtained from the selected effective photoelectric conversion elements.

15. An apparatus according to claim 14, further comprising:

determining means for determining whether there is a designation device or not, by comparing the first threshold value set by said first threshold setting means with the second threshold value set by said second threshold setting means.

16. An apparatus according to claim 14, further comprising a display device.

17. A method for controlling an apparatus for outputting position information corresponding to light having a cyclically varying intensity, comprising the step of:

detecting by a detection device that receives the light, said detection device comprising a plurality of photoelectric conversion elements, arranged in a predetermined physical array;

generating, for each photoelectric conversion element, a difference signal corresponding to a difference between an output of the photoelectric conversion element when the light cycle is at a first point and an output of the photoelectric conversion element when the light cycle is at a second point, the first point being at a higher intensity than the second point;

setting a threshold value on the basis of a level of said difference signal obtained from each photoelectric conversion element;

selecting effective photoelectric conversion elements by comparing said threshold value with the difference signal generated in said difference signal generating step; and

outputting the difference signals corresponding to the selected effective photoelectric conversion elements.

18. A method for controlling an apparatus for outputting position information corresponding to light having a cyclically varying intensity, comprising the step of:

detecting by a detection device that receives the light, said detection device comprising a plurality of photoelectric conversion elements, arranged in a predetermined physical array;

generating, for each photoelectric conversion element, a difference signal corresponding to a difference between an output of the photoelectric conversion element when the light cycle is at a first point and an output of the photoelectric conversion element when the light cycle is at a second point, the first point being at a higher intensity than the second point;

setting a first threshold value on the basis of a mean value of output of said difference signal obtained from each photoelectric conversion element;

setting a second threshold value to either one of the outputted difference signals of a photoelectric conversion element having the largest difference signal and two photoelectric conversion elements equally spaced by the predetermined number of pixels from the photoelectric conversion element having the largest difference signal;

selecting effective photoelectric conversion elements by comparing said first threshold value and said second threshold value with the difference signal generated in said difference signal generating step; and

outputting the difference signals obtained from the selected effective photoelectric conversion elements.

19. A coordinate input apparatus for outputting position information corresponding to light having a cyclically varying intensity, said apparatus comprising:

a detection device that receives the light, said detection device comprising a plurality of photoelectric conversion elements, arranged in a predetermined physical array;

difference signal generating means for generating, for each photoelectric conversion element, a difference signal corresponding to a difference between an output of the photoelectric conversion element when the light cycle is at a first point and an output of the photoelectric conversion element when the light cycle is at a second point, the first point being at a higher intensity than the second point;

threshold setting means for setting a threshold value on the basis of a level of said difference signal obtained from each photoelectric conversion element;

selection means for selecting effective photoelectric conversion elements by comparing said threshold value with the difference signal generated by said difference signal generating means; and

output means for outputting the difference signals corresponding to the selected effective photoelectric conversion elements.

20. A coordinate input apparatus for outputting position information corresponding to light having a cyclically varying intensity, said apparatus comprising:

a detection device that receives the light, said detection device comprising a plurality of photoelectric conversion elements, arranged in a predetermined physical array;

difference signal generating means for generating, for each photoelectric conversion element, a difference signal corresponding to a difference between an output of the photoelectric conversion element when the light cycle is at a first point and an output of the photoelectric conversion element when the light cycle is at a second point, the first point being at a higher intensity than the second point;

first threshold setting means for setting a first threshold value on the basis of a mean value of output of said difference signal obtained from each photoelectric conversion element;

second threshold setting means for setting a second threshold value to either one of the outputted difference signals of a photoelectric conversion element having the largest difference signal and two photoelectric conversion elements equally by spaced the predetermined number of pixels from the photoelectric conversion element having the largest difference signal;

selection means for selecting effective photoelectric conversion elements by comparing said first threshold value and said second threshold value with the difference signal generated by said difference signal generating means; and

output means for outputting the difference signal obtained from the selected effective photoelectric conversion elements.