Image data processing circuit and image data processing method

• US 20070139539A1
• Filed: 03/22/2006
• Published: 06/21/2007
• Est. Priority Date: 12/16/2005
• Status: Active Grant

• Current Assignee: Socionext Inc.
• Original Assignee: Fujitsu Limited
• Inventors: Fukuoka, Tomohiro, Ohara, Kunihiro
• Granted Patent: US 7,800,660 B2
• Time in Patent Office: Days
• US Class Current: 348/243
• CPC Class Codes: H04N 23/95 Computational photography systems, e.g. light-field imaging systems
• CPC Class Codes: H04N 25/63 applied to dark current
• CPC Class Codes: H04N 25/633 by using optical black pixels
• CPC Class Codes: H04N 25/673 by using reference sources
• CPC Class Codes: H04N 25/772 comprising A/D, V/T, V/F, I/T or I/F converters

Abstract

An object of the present invention is to provide an image data processing circuit and an image data processing method capable of determining a reference signal level corresponding to black in an image with high precision by suppressing occurrence of line dependency and the like in a dark current component signal included in image data output from a solid state image pickup device. A reference dark current component data holding unit selects a reference line from a solid state image pickup device and holds a dark current component of the reference line as a head line average value. To a subtraction circuit, dark current component data and effective pixel data is sequentially input on the line unit basis. A differential circuit obtains, as a detection value, a change amount with respect to the head line average value, of the dark current component data included in a preceding line. The subtraction circuit subtracts the detection value from the dark current component data and the effective pixel data entered.

Claims

1. An image data processing circuit of a solid state image pickup device from which a dark current component signal and a pixel signal are sequentially output on a line unit basis, comprising:

a first holding circuit for holding the dark current component signal in a reference line as a reference dark current component signal;

a first subtraction circuit to which the dark current component signal and the pixel signal are sequentially entered on the line unit basis; and

a differential circuit for obtaining, as a dark current change amount, a change amount with respect to the reference dark current component signal, of the dark current component signal included in a preceding line output from the solid state image pickup device prior to the line entered to the first subtraction circuit,

wherein the first subtraction circuit subtracts the dark current change amount from the dark current component signal and the pixel signal which are entered.

2. An image data processing circuit according to claim 1, wherein the first holding circuit sets “

i”

lines from the first line to the i-th line (where i is a natural number of 2 or larger) as the reference lines and holds an average value of the dark current component signals included in the reference lines as the reference dark current component signal, and

the subtraction circuit uses, as the preceding lines, the (i+1)th line and subsequent lines which are j lines (j;

natural number of two or larger) preceding the line entered to the first subtraction circuit and obtains, as a dark current change amount, a change amount with respect to the reference dark current component signal, of an average value of the dark current component signals included in the preceding lines.

3. An image data processing circuit according to claim 1, wherein the first holding circuit uses a first line as the reference line, and holds an average value of the dark current component signals included in the reference line as the reference dark current component signal, and

the differential circuit uses, as the preceding line, a line which is any of the second and subsequent lines and immediately precedes the line entered to the first subtraction circuit and obtains, as a dark current change amount, a change amount with respect to the reference dark current component signal, of an average of the dark current component signals included in the preceding line.

4. An image data processing circuit according to claim 1, further comprising:

a second holding circuit for holding, as a dark current change amount of last time, the dark current change amount in the line immediately preceding the line entered to the first subtraction circuit; and

a first limiter, when an increase amount of the dark current change amount in the line entered to the first subtraction circuit with respect to the dark current change amount of last time exceeds a predetermined increase amount upper limit value, using, as the dark current change amount, a value obtained by adding the increase amount upper limit value to the dark current change amount of last time.

5. An image data processing circuit according to claim 4, wherein when the change amount with respect to the dark current change amount of last time, of the dark current change amount is a negative value, the first limiter sets the value of the dark current change amount to zero.

6. An image data processing circuit according to claim 1, further comprising:

a second holding circuit for holding, as a dark current change amount of last time, the dark current change amount in the line immediately preceding the line entered to the first subtraction circuit; and

a second limiter, when a decrease amount with respect to the dark current change amount of last time, of the dark current change amount in the line entered to the first subtraction circuit exceeds a predetermined decrease amount upper limit value, using, as the dark current change amount, a value obtained by subtracting the decrease amount upper limit value from the dark current change amount of last time.

7. An image data processing circuit according to claim 6, wherein when the change amount with respect to the dark current change amount of last time, of the dark current change amount is a positive value, the second limiting circuit sets the value of the dark current change amount to zero.

8. An image data processing circuit according to claim 1, further comprising a mask circuit which is provided on a connection path between the solid state image pickup device and the first holding circuit and the differential circuit and masks the dark current component signal exceeding a predetermined dark current component signal threshold.

9. An image data processing circuit according to claim 1, further comprising:

a second subtraction circuit to which the dark current component signal and the pixel signal as analog signals output from the solid state image pickup device are entered;

a first selector to which an output of the solid state image pickup device and an output of the second subtraction circuit are entered;

an AD converter provided on a connection path between the first selector and the first subtraction circuit and converting an analog output of the first selector to a digital output; and

a second selector to which an output of the first subtraction circuit and an output of the AD converter are entered,

wherein in the case where a subtracting process of subtracting the dark current change amount from the dark current component signal and the pixel signal is performed in the first subtraction circuit, the first selector selects an output of the solid state image pickup device and the second selector selects an output of the first subtraction circuit, and

in the case where the subtracting process is performed in the second subtraction circuit, the first selector selects an output of the second subtraction circuit and the second selector selects an output of the AD converter.

10. An image data processing circuit according to claim 1, wherein the differential circuit updates the dark current change amount every predetermined number of preceding lines.

11. An image data processing method of a solid state image pickup device from which a dark current component signal and a pixel signal are sequentially output on a line unit basis, comprising:

a step of holding the dark current component signal in a reference line as a reference dark current component signal;

a step of sequentially inputting the dark current component signal and the pixel signal on the line unit basis;

a step of obtaining, as a dark current change amount, a change amount with respect to the reference dark current component signal, of the dark current component signal included in a preceding line output from the solid state image pickup device prior to the lines which are sequentially entered on the line unit basis; and

a step of subtracting the dark current change amount from the dark current component signal and the pixel signal which are sequentially entered on the line unit basis.