Image sensing apparatus

• US 20020024601A1
• Filed: 07/30/2001
• Published: 02/28/2002
• Est. Priority Date: 08/01/2000
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Tashiro, Kazuaki, Kaifu, Noriyuki, Yuki, Osamu
• Granted Patent: US 6,947,084 B2
• Time in Patent Office: Days
• US Class Current: 348/207.99
• CPC Class Codes: H04N 25/63 applied to dark current
• CPC Class Codes: H04N 5/325 Image enhancement, e.g. by subtraction techniques using polyenergetic X-rays

Abstract

An image sensing apparatus including an X-ray image sensing unit having a non-destructive read function, adapted to sense an oject image, and a subtractor adapted to sequentially output as a corrected value a difference between a plurality of frames sequentially read out non-destructively from the X-ray image sensing unit and a frame read out before the plurality of frames.

Claims

1. An image sensing apparatus comprising:

an image sensing unit having a non-destructive read function, adapted to an object image; and

a subtractor circuit adapted to sequentially output a plurality of corrected values, wherein each of said plurality of corrected values is a difference between a first frame included in a plurality of frames sequentially read out non-destructively from said image sensing unit and a second frame included in said plurality of frames, read out before the first frame.

2. An image sensing apparatus according to claim 1, further comprising a driver circuit including a comparator circuit for comparing the output value read out from said image sensing unit with a reference value, said driver circuit changing a read mode of said image sensing unit to a normal read mode if the output value exceeds the reference value, wherein the normal read mode resets said image sensing unit and reads out a signal after the reset.

3. An image sensing apparatus according to claim 1, wherein said image sensing unit has pixel portions each including a photoelectric conversion element and a transistor for reading, the photoelectric element of the pixel portion being connected to a control terminal of said transistor.

4. An image sensing apparatus according to claim 3, wherein a load is connected to one non-control terminal of said transistor and constitutes an amplifier having a voltage gain of about 1.

5. An image sensing apparatus according to claim 4, wherein said load is a constant current source or a resistor.

6. An image sensing apparatus according to claim 3, wherein a switching transistor is connected serially to said transistor in order to select the pixel portions in a row direction.

7. An image sensing apparatus according to claim 2, wherein a transistor for reset is connected serially to the photoelectric conversion element, and said driver circuit controls said transistor for reset by using a mode switching signal to change the read mode either to the normal read mode or to the non-destructive read mode.

8. An image sensing apparatus according to claim 2, further comprising a memory table for storing position information of a defective pixel of said image sensing unit, wherein said driver circuit does not change the read mode if an output value for the defective value is to be output, by referring to the position information stored in said memory table.

9. An image sensing apparatus according to claim 2, wherein further comprising a memory table for storing position information of an invalid area other than an image sensing area of said image sensing unit, wherein said driver circuit does not change the read mode if an output value for the invalid area is to be output, by referring to the position information stored in said memory table.

10. An image sensing apparatus according to claim 2, further comprising a counter connected to an output portion of the comparator circuit, wherein said counter counts the number of times when the output value read out from said image sensing unit exceeds the reference value, and said driver circuit changes the read mode from the non-destructive read mode to the normal read mode when the count of said counter reaches a predetermined value.

11. An image sensing apparatus according to claim 2, further comprising a memory circuit adapted to storing the corrected values for each frame, wherein for the frame following the normal read mode, a corrected value for the previous frame stored in said memory circuit is output.