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EP-4738859-A1 - IMAGE-CAPTURING SYSTEM WITH CURRENT-CONTROLLED ILLUMINATION

EP4738859A1EP 4738859 A1EP4738859 A1EP 4738859A1EP-4738859-A1

Abstract

The present disclosure relates to an image-capturing system (100) comprising: an image sensor (101) configured to capture images of a scene at a periodic rate; an illumination source (102) for illuminating the scene; measurement and control circuitry (108) configured to: continuously measure a current (200) to/from the image sensor (101); continuously detect periodically alternating high and low levels (202; 203) of the measured current (200); and control the illumination source (102) to alternate between an on state and an off state with an illumination frequency equal to a switching frequency of the detected periodically alternating high and low levels (202; 203) of the measured current (200) such that the illumination source (102) is in the on state during exposure of the image sensor (101). The disclosure further relates to a method (300) of controlling an illumination source for illuminating a scene during image sensor exposures.

Inventors

  • Grawé, Markus

Assignees

  • Axis AB

Dates

Publication Date
20260506
Application Date
20241030

Claims (15)

  1. An image-capturing system (100) comprising: an image sensor (101) configured to capture images of a scene at a periodic rate; an illumination source (102) for illuminating the scene; measurement and control circuitry (108) configured to: continuously measure a current (200) to/from the image sensor (101); continuously detect periodically alternating high and low levels (202; 203) of the measured current (200); and control the illumination source (102) to alternate between an on state and an off state with an illumination frequency equal to a switching frequency of the detected periodically alternating high and low levels (202; 203) of the measured current (200) such that the illumination source (102) is in the on state during exposure of the image sensor (101).
  2. The image-capturing system (100) according to claim 1, wherein at least the image sensor (101) and the measurement and control circuitry (108) are disposed in different units (106; 110), such as on different printed circuit boards.
  3. The image-capturing system (100) according to any one of the preceding claims, wherein the image sensor (101) and the illumination source (102) are disposed in different units (106; 107).
  4. The image-capturing system (100) according to any one of the preceding claims, wherein the measurement and control circuitry (108) is configured to generate an enable signal (204a; 204b) for controlling the illumination source (102) to illuminate and not illuminate the scene.
  5. The image-capturing system (100) according to any one of the preceding claims, wherein the measurement and control circuitry (108) comprises measurement circuitry (104), such as at least one shunt resistor, for measuring the current, and control circuitry (105), such as a comparator, for generating an enable signal (204a; 204b) for controlling the illumination source (102) to illuminate and not illuminate the scene.
  6. The image-capturing system (100) according to any one of the preceding claims, wherein the high levels (202) are current levels higher than a predefined current threshold (201) and the low levels (203) are current levels lower than the predefined current threshold (201).
  7. The image-capturing system (100) according to any one of the preceding claims, wherein the image sensor (101) is configured to capture images of the scene at a rate of at least 10 image frames per second, preferably at least 30 image frames per second, corresponding to an illumination frequency of at least 10 Hz.
  8. The image-capturing system (100) according to any one of the preceding claims, wherein the measured current (202) has distinct high and low current levels (202; 203) correlating with an active and an inactive state of the image sensor.
  9. The image-capturing system (100) according to claim 8, wherein the measurement and control circuitry (108) is configured to compare the measured current (200) against a predefined threshold (201) to determine whether the image sensor is in the active or inactive state.
  10. The image-capturing system (100) according to any one of the preceding claims, wherein the measurement and control circuitry (108) is configured to determine, based on the detected level or change in the measured current (202), a time period during which the image sensor (101) performs exposure.
  11. The image-capturing system (100) according to claim 10, wherein the measurement and control circuitry (108) is configured to convert the change in the measured current (202) to the time period during which the image sensor (101) performs exposure according to a predetermined relationship and/or function.
  12. The image-capturing system (100) according to any one of claims 10 to 11, wherein the measurement and control circuitry (108) is configured to determine the time period during which the image sensor (101) performs exposure comprises using a model of the image sensor.
  13. The image-capturing system (100) according to any one of the preceding claims, wherein the measurement and control circuitry (108) is configured to control the illumination source (102) to alternate between the on state and the off state with a predetermined time offset relative to a distinct change in the measured current (200).
  14. The image-capturing system (100) according to any one of the preceding claims, wherein the illumination source is an infrared illumination source, such as an infrared illumination light-emitting diode.
  15. A method (300) of controlling an illumination source for illuminating a scene during image sensor exposures, the method comprising: configuring (301) an image sensor to capture images of a scene at a periodic rate; continuously measuring (302) a current to/from the image sensor; continuously detecting (303) periodically alternating high and low levels of the measured current; and controlling (304) the illumination source to alternate between an on state and an off state with an illumination frequency equal to a switching frequency of the detected periodically alternating high and low levels of the measured current such that the illumination source is in the on state during exposure of the image sensor.

Description

The present disclosure relates to an image-capturing system with current-controlled illumination, specifically designed to optimize power consumption by synchronizing the illumination with the exposure time of the image sensor. The disclosure further relates to a method of controlling an illumination source, such as an infrared light-emitting diode (LED), for illuminating a scene during the exposure periods of the image sensor, even in systems where the image sensor lacks a dedicated exposure signal output. Background In modern network camera systems, infrared (IR) illumination plays a critical role in capturing clear images in low-light conditions. Typically, these systems rely on IR light-emitting diodes (LEDs) to illuminate the scene, ensuring that the image sensor can capture detailed images even in darkness. In the current state of the art, IR LEDs are often continuously powered, regardless of whether the image sensor is actively capturing an image. This approach, while ensuring that sufficient illumination is available when needed, leads to significant power consumption. A common practice to reduce power consumption is to synchronize the IR illumination with the exposure time of the image sensor. In systems where the image sensor provides a dedicated output signal indicating the exposure period, this synchronization can be effectively implemented. However, not all image sensors are equipped with such an output signal, making it challenging to control the IR illumination. The disadvantage of the existing solutions is twofold. First, in systems lacking an exposure signal from the image sensor, there is no straightforward method to accurately time the IR illumination with the sensor's exposure period. This results in continuous or excessively long periods of IR LED operation, leading to increased power consumption and reduced operational efficiency. Second, even in systems where some form of synchronization is possible, the reliance on external signals or complex configurations can complicate the design and increase costs. It is therefore an objective of the present disclosure to provide a solution that enables precise control of IR illumination in network camera systems, particularly in those where the image sensor does not provide a direct signal indicating the exposure time. This solution aims to optimize power consumption by ensuring that the IR LEDs are active when needed, thus improving the energy efficiency of the camera system without requiring additional signaling from the sensor. Summary The present disclosure relates to an image-capturing system comprising an image sensor configured to capture images of a scene at a periodic rate, an illumination source for illuminating the scene, and measurement and control circuitry configured to continuously measure a current to or from the image sensor, continuously detect periodically alternating high and low levels of the measured current, and control the illumination source to alternate between an on state and an off state with an illumination frequency equal to a switching frequency of the detected periodically alternating high and low levels of the measured current such that the illumination source is in the on state during exposure of the image sensor. This system enables precise synchronization of the illumination source with the exposure time of the image sensor, thereby optimizing energy consumption in network camera systems. By monitoring the current flowing to or from the image sensor, the system can detect patterns in the current that correlate with the sensor's exposure periods. This allows the illumination source to be activated only during the times when the image sensor is actively capturing images, reducing unnecessary power usage. This is particularly beneficial in systems where the image sensor does not provide a direct signal indicating its exposure time, as the invention leverages the detected current fluctuations to infer the appropriate timing for the illumination. The inventor has realized that there exists a correlation between the switching frequency of the periodically alternating high and low levels of the current and an exposure frequency, and that this correlation can be used to control the illumination source. This has enabled a method of controlling the illumination source without requiring a direct signal from the image sensor indicating when it is actively exposing, but instead using an illumination frequency that is equal to the switching frequency of the detected periodically alternating high and low levels. The inventor has observed that the image sensor draws varying amounts of current during its operational cycle, with distinct peaks and troughs that correspond to different phases of the sensor's operation. Specifically, during the exposure phase, when the sensor is capturing image data, there is a notable increase in current draw. This higher current level is followed by a reduction during idle or non-exposure period