BLACK-LEVEL FEEDBACK DEVICE, IMAGE READING DEVICE, AND BLACK-LEVEL FEEDBACK CONTROL METHOD

Abstract

A first set-value calculating unit calculates a first set value of a black-level feedback based on a reflection amount that increases a speed of tracking to a black-level target value in a black-level feedback control. A second set-value calculating unit calculates a second set value of a black-level feedback based on a reflection amount that slows down a tracking to a black-level target value as compared to the speed of tracking of the first set-value calculating unit. A selecting unit selects and outputs any one of the first set value and the second set value and outputs selected value as a set value. A controlling unit controls selection of any one of the first set value and the second set value by the selecting unit based on the black differential value and a gain of the image data.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a configuration of an image scanner according to a first embodiment of the present invention;

FIG. 2 is a block diagram of a configuration of a signal processing IC incorporated in an image scanner;

FIG. 3 is a block diagram of a configuration of a set value calculator;

FIG. 4 is a graph of a threshold level of a tracking-speed determining unit;

FIG. 5 is a flowchart of a black-level correction process as an operation example of a black-level feedback control;

FIG. 6 is a block diagram of a configuration of a set value calculator according to a second embodiment of the present invention;

FIG. 7 is a graph of a threshold level of a tracking-speed determining unit;

FIG. 8 is a flowchart of a black-level correction process as an operation example of a black-level feedback control;

FIG. 9 is a graph of a threshold level of a tracking-speed determining unit according to a third embodiment of the present invention;

FIG. 10 is a block diagram of a configuration of a set value calculator according to a fourth embodiment of the present invention;

FIG. 11 is a graph of a threshold level of a tracking-speed determining unit;

FIG. 12 is a graph of a threshold level of a tracking-speed determining unit according to a fifth embodiment of the present invention;

FIG. 13 is a block diagram of a configuration of a set value calculator according to a sixth embodiment of the present invention;

FIG. 14 is a timing chart of timings of an XSLSYNC signal and a DAC_opcnt signal;

FIG. 15 is a block diagram of a configuration of a signal processing IC incorporated in an image scanner according to a seventh embodiment of the present invention;

FIG. 16 is a timing chart of timings of an XSLSYNC signal and a BLKCLP signal;

FIG. 17 is a block diagram of a configuration of a signal processing IC incorporated in an image scanner according to an eighth embodiment of the present invention;

FIG. 18 is a timing chart of timings of an XSLSYNC signal, a DAC_opcnt signal, and an ave_clr signal;

FIG. 19 is a block diagram of a configuration of a set value calculator according to a ninth embodiment of the present invention;

FIG. 20 is a schematic of an “H” period of a BLKCLP signal according to a tenth embodiment of the present invention;

FIG. 21 is a block diagram of a configuration of a signal processing IC incorporated in a conventional image reading device;

FIG. 22 is a schematic of an image format of image data output from a CCD;

FIG. 23 is graph of frequency spread by an SSCG;

FIG. 24 is a graph of occurrence of high and low image levels; and

FIG. 25 is a schematic of a process in which a sub-scanning image level variation occurs.

Claims

1. A black-level feedback device that executes a black-level feedback control that includes converging a black detection level to a black-level target value, based on a black differential value between the black detection level obtained by averaging assigned pixels of image data in one line output from a photoelectric conversion element during a black-level period or a period corresponding to a black level and the black-level target value determined in advance, the black-level feedback device comprising: a first set-value calculating unit that calculates and outputs a first set value of a black-level feedback based on a reflection amount that increases a speed of tracking to the black-level target value in the black-level feedback control;a second set-value calculating unit that calculates and outputs a second set value of a black-level feedback based on a reflection amount that slows down a speed of tracking to the black-level target value as compared to the speed of tracking of the first set-value calculating unit;a selecting unit that selects any one of the first set value and the second set value and outputs selected value as a set value; anda controlling unit that controls selection of any one of the first set value and the second set value by the selecting unit based on the black differential value and a gain of the image data.

2. The black-level feedback device according to claim 1, wherein the controlling unit controls a threshold level based on the gain of the image data when controlling the selection by the selecting unit.

3. The black-level feedback device according to claim 1, wherein the controlling unit causes the second set-value calculating unit slow down the tracking of the image level variation due to a spread spectrum clock generator (SSCG), and causes the first set-value calculating unit speeds-up the tracking the image level variation due to smear when controlling the selection by the selecting unit.

4. The black-level feedback device according to claim 1, wherein the controlling unit controls the output of the selecting unit according to the black differential value and the gain of the image data, and stops the black-level feedback within a constant range of the black differential value, at the time of selecting the output from the first set-value calculating unit or the output from the second set-value calculating unit.

5. The black-level feedback device according to claim 4, wherein the constant range is a range within threshold levels in which the black differential value can be permitted as a black-level variation.

6. The black-level feedback device according to claim 1, wherein the threshold levels have a hysteresis characteristic.

7. An image reading device that executes, at the time of outputting a digital image signal after reading an image by a photoelectric converting element, a black-level feedback control that includes converging a black detection level to a black-level target value, based on a black differential value between the black detection level obtained by averaging assigned pixels of image data in one line output from the photoelectric conversion element during a black-level period or a period corresponding to a black level and the black-level target value determined in advance, the image reading device comprising: a first set-value calculating unit that calculates and outputs a first set value of a black-level feedback based on a reflection amount that increases a speed of tracking to the black-level target value in the black-level feedback control;a second set-value calculating unit that calculates and outputs a second set value of a black-level feedback based on a reflection amount that slows down a speed of tracking to the black-level target value as compared to the speed of tracking of the first set-value calculating unit;a selecting unit that selects any one of the first set value and the second set value and outputs selected value as a set value; anda controlling unit that controls selection of any one of the first set value and the second set value by the selecting unit based on the black differential value and a gain of the image data.

8. The image reading device according to claim 7, wherein the controlling unit controls a threshold level based on the gain of the image data when controlling the selection by the selecting unit.

9. The image reading device according to claim 7, wherein the controlling unit causes the second set-value calculating unit slow down the tracking of the image level variation due to a spread spectrum clock generator (SSCG), and causes the first set-value calculating unit speeds-up the tracking the image level variation due to smear when controlling the selection by the selecting unit.

10. The image reading device according to claim 7, wherein the controlling unit controls the output of the selecting unit according to the black differential value and the gain of the image data, and stops the black-level feedback within a constant range of the black differential value, at the time of selecting the output from the first set-value calculating unit or the output from the second set-value calculating unit.

11. The image reading device according to claim 10, wherein the constant range is a range within threshold levels in which the black differential value can be permitted as a black-level variation.

12. The image reading device according to claim 7, wherein the threshold levels have a hysteresis characteristic.

13. A image reading device that executes a black-level feedback control that includes converging a black detection level to a black-level target value, based on a black differential value between the black detection level obtained by averaging assigned pixels of image data in one line output from a photoelectric conversion element during a black-level period or a period corresponding to a black level and the black-level target value determined in advance, the black-level feedback device comprising: a line-interval assigning unit that executes the black-level feedback control at line intervals at which black-level variation phases coincide with each other.

14. The image reading device according to claim 13, wherein the line-interval assigning unit assigns an execution line interval of the black-level feedback control based on an external control signal.

15. The image reading device according to claim 13, wherein the black-level detection in the black-level feedback control is calculated from an average value between lines in which black-level variation phases coincide with each other.

16. The image reading device according to claim 13, further comprising a differential-value comparing unit that compares the black differential value with a threshold level, wherein when the differential value comparing unit determines that the black differential value exceeds the threshold level, the black-level feedback device executes the black-level feedback control for each line, regardless of the assignment of an execution line interval assigned by the line interval assigning unit.