Night vision system and control method thereof

• US 20030160153A1
• Filed: 02/24/2003
• Published: 08/28/2003
• Est. Priority Date: 02/27/2002
• Status: Active Grant

• Current Assignee: DENSO Corporation, Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: DENSO Corporation
• Inventors: Eguchi, Shotaro, Kawamata, Shinya, Hagisato, Yasuo, Yamaguchi, Ryuji, Hara, Yoshimasa, Toyofuku, Kunihiko
• Granted Patent: US 7,045,759 B2
• Time in Patent Office: Days
• US Class Current: 250/214VT
• CPC Class Codes: H04N 23/21 from near infrared [NIR] radiation
• CPC Class Codes: H04N 23/74 by influencing the scene brightness using illuminating means
• CPC Class Codes: H04N 23/76 by influencing the image signals
• CPC Class Codes: H04N 23/82 for controlling camera response irrespective of the scene brightness, e.g. gamma correction
• CPC Class Codes: H04N 5/202 Gamma control circuits for controlling camera response irrespective of the scene brightness H04N23/82

Abstract

A second circuit separately extracts a synchronization signal and brightness signal from an image signal output from a camera for capturing an image of a subject. A gamma amplifier produces a gamma correction signal based on a brightness ratio characteristic in which a display brightness increases as the signal level of the brightness signal increases and the display brightness is set using a display brightness correction ratio which is preferably 70 to 90% of an equi-proportional display brightness correction ratio when the signal level of the brightness signal falls in a high-brightness range. A liquid crystal display receives the gamma correction signal and displays an image captured by the camera with the display brightness set in accordance with the brightness ratio characteristic while synchronizing with a drive timing signal output from a first circuit. Thus, the difference in display brightness between different high-brightness regions or subjects is made large, whereby halation which may otherwise occur between those regions or subjects can be prevented.

Claims

1. A night vision system, comprising:

a display; and

a controller that displays an image on the display, the controller including a gamma amplifier which;

receives a brightness signal constituting an image signal indicative of an image to be displayed on the display;

produces a gamma correction signal from the brightness signal based on a brightness ratio characteristic in which a display brightness is set to a maximum brightness using a first brightness correction ratio when a signal level of the brightness signal is a maximum signal level, and the display brightness is set using a second brightness correction ratio which is lower than the first brightness correction ratio when the signal level of the brightness signal is lower than the maximum signal level; and

outputs the produced gamma correction signal to the display.

2. The night vision system according to claim 1, wherein

the controller further comprises a first circuit which generates a drive timing signal in accordance with a synchronization signal constituting the image signal;

and

the display receives the gamma correction signal and displays an image with the display brightness set in accordance with the brightness ratio characteristic while synchronizing with the drive timing signal.

3. The night vision system according to claim 2, further comprising:

a camera for capturing an image of a subject located outside of a vehicle; and

a combiner portion which creates a virtual image by reflecting an image projected by the display, the night vision system being further characterized in that;

the controller further comprises a second circuit which receives an image signal output from the camera and separately extracts the brightness signal and the synchronization signal from the received image signal.

4. The night vision system according to claim 3, further comprising:

a lamp for emitting a light towards a subject, the night vision system being further characterized in that;

the camera captures an image including the light reflected by the subject.

5. The night vision system according to claim 4, wherein the lamp emits an infrared light, and the camera captures an image including the infrared light.

6. The night vision system according to claim 5, wherein the infrared light includes a near-infrared light.

7. The night vision system according to claim 1, wherein:

the brightness ratio characteristic is determined such that the display brightness increases as the signal level of the brightness signal increases

the signal level is divided into a plurality of steps of a predetermined range each, and the brightness ratio characteristic is determined such that the display brightness is set to the maximum brightness using an equi-proportional display brightness correction ratio when a signal level of the brightness signal falls in a range of a step corresponding to a maximum signal level and the display brightness is set using a display brightness correction ratio which is 70 to 90% of the equi-proportional display brightness correction ratio when the signal level of the brightness signal falls in a range of a step which is one step lower than the step corresponding to the maximum signal level.

8. The night vision system according to claim 7, wherein the plurality of steps comprise eleven steps.

9. The night vision system according to claim 1, further comprising a gamma adjuster for adjusting the brightness ratio characteristic.

10. The night vision system according to claim 9, wherein the gamma adjuster adjusts the brightness ratio characteristic so as to change the second display brightness correction ratio used for setting the display brightness when the signal level of the brightness signal falls in a range of a step which is one step lower than the step corresponding to the maximum signal level.

11. A control method for a night vision system, comprising

receiving a brightness signal constituting an image signal indicative of an image to be displayed on a display;

setting a display brightness to a maximum brightness using an equi-proportional display brightness correction ratio when a signal level of the brightness signal is a maximum signal level; and

setting a display brightness using a display brightness correction ratio that is lower than the equi-proportional display brightness correction ratio when the signal level of the brightness signal is lower than the maximum signal level.

12. The method according to claim 11, further comprising

displaying an image with the display brightness set in accordance with the brightness ratio characteristic while synchronizing with a drive timing signal generated in accordance with a synchronization signal constituting the image signal.

13. The method according to claim 12, further comprising

separately extracting the brightness signal and the synchronization signal from the image signal.

14. The method according to claim 13, further comprising:

emitting a light towards a subject, and

capturing an image including the light reflected by the subject.

15. The method according to claim 14, wherein the light includes an infrared light.

16. The method according to claim 15, wherein the infrared light includes a near-infrared light.

17. The method according to claim 11, wherein:

the brightness ratio characteristic is determined such that the display brightness increases as the signal level of the brightness signal increases

the signal level is divided into a plurality of steps of a predetermined range each, and the brightness ratio characteristic is determined such that the display brightness is set to the maximum brightness using an equi-proportional display brightness correction ratio when a signal level of the brightness signal falls in a range of a step corresponding to a maximum signal level and the display brightness is set using a display brightness correction ratio which is 70 to 90% of the equi-proportional display brightness correction ratio when the signal level of the brightness signal falls in a range of a step which is one step lower than the step corresponding to the maximum signal level.

18. The method according to claim 17, wherein the plurality of steps are eleven steps.

19. The method according to claim 11, further comprising

adjusting the brightness ratio characteristic.

20. The method according to claim 19, wherein the brightness ratio characteristic is adjusted so as to change the second brightness correction ratio used for setting the display brightness when the signal level of the brightness signal falls in a range of a step which is one step lower than the step corresponding to the maximum signal level.