Method and system for automatic gain control of sensors in time-of-flight systems

For use with a time-of-flight (TOF) system that illuminates a target, a distance z from said TOF system, with emitted optical energy having a modulated periodic waveform that includes a high frequency component, and that detects a fraction of said emitted optical energy with an array of pixel photodetectors operable in at least two phases to determine data proportional to said distance z, said TOF system operable to determine distance z independently of reflectivity of said target, a control system to automatically control detection gain of said pixel photodetectors, the control system comprising:

• means for identifying which of said pixel photodetectors are receiving excessive levels of emitted optical energy to output reliable detection data, which of said pixel photodetectors are receiving insufficient levels of emitted optical energy to output reliable detection data, and which of said pixel photodetectors are receiving adequate levels of emitted optical energy to output reliable detection data;
• means for designating one of at least three groups into which pixel photodetectors identified by said means for identifying are placed, designation choices comprising (i) said pixel photodetectors receiving excessive levels of emitted optical energy, (ii) said pixel photodetectors receiving insufficient levels of emitted optical energy, and (iii) said pixel photodetectors receiving adequate levels of emitted optical energy;
• and
• means for varying at least one system parameter associated with said TOF system;
• wherein said means for varying varies at least one system parameter associated with said TOF system to reduce levels of emitted optical energy presented to said pixel photodetectors if said means for designating determines that a highest number of said pixel photodetectors are members of a group comprising said pixel photodetectors receiving excessive levels of emitted optical energy;
• and
• wherein said means for varying varies at least one system parameter associated with said TOF system to increase levels of emitted optical energy presented to said pixel photodetectors if a highest number of said pixel photodetectors are members of a group comprising said pixel photodetectors receiving insufficient levels of emitted optical energy.

For use with a time-of-flight (TOF) system that illuminates a target, a distance z from said TOF system, with optical energy having a modulated periodic waveform that includes a high frequency component, and that detects a fraction of said illumination with an array of pixel photodetectors operable in at least two phases to determine data proportional to said distance z, said TOF system operable to determine distance z independently of ambient light, a method to automatically control detection gain of said pixel photodetectors, the method comprising the following steps:

• (a) identifying from a passive brightness image acquired by said TOF system which of said pixel photodetectors are receiving excessive levels of emitted optical energy to output reliable detection data, and identifying from an active brightness image which of said pixel photodetectors are receiving insufficient levels of emitted optical energy to output reliable detection data and forming a histogram of such identification;
• (b) using identification information from step (a) to form a histogram representing number of said pixel photodetectors receiving excessive levels of emitted optical energy, number of said pixel photodetectors receiving insufficient levels of emitted optical energy, and number of said pixel photodetectors receiving neither excessive nor insufficient levels of emitted optical energy;
• (c) estimating variation in at least one system parameter of said TOF system to produce a change in light ΔL that increases said number of said pixel photodetectors receiving neither excessive nor insufficient levels of emitted optical energy;
• (d) varying at least one system parameter of said TOF system to increase said number of said pixel photodetectors receiving neither excessive nor insufficient levels of emitted optical energy.

For use with a time-of-flight (TOF) system that illuminates a target, a distance z from said TOF system, with emitted optical energy having a modulated periodic waveform that includes a high frequency component, and that detects a fraction of said emitted optical energy with an array of pixel photodetectors operable in at least two phases to determine data proportional to said distance z, said TOF system operable to determine distance z independently of ambient light, a control system to automatically control detection gain of said pixel photodetectors, said control system comprising:

• means for identifying from a passive brightness image acquired by said TOF system which of said pixel photodetectors are receiving excessive levels of emitted optical energy to output reliable detection data, and for identifying from an active brightness image which of said pixel photodetectors are receiving insufficient levels of emitted optical energy to output reliable detection data and forming a histogram of such identification;
• means for forming a histogram, using identification information from said means for identifying, representing number of said pixel photodetectors receiving excessive levels of emitted optical energy, number of said pixel photodetectors receiving insufficient levels of optical energy, and number of said pixel photodetectors receiving neither excessive nor insufficient levels of emitted optical energy;
• means for estimating variation in at least one system parameter of said TOF system to produce a change in light ΔL that increases said number of said pixel photodetectors receiving neither excessive nor insufficient levels of emitted optical energy;
• and
• means for varying at least one system parameter of said TOF system to increase said number of said pixel photodetectors receiving neither excessive nor insufficient levels of emitted optical energy.

For use with a time-of-flight (TOF) system that illuminates a target, a distance z from said TOF system, with emitted optical energy having a modulated periodic waveform that includes a high frequency component, and that detects a fraction of said emitted optical energy with an array of pixel photodetectors operable in at least two phases to determine data proportional to said distance z, said TOF system operable independently of ambient light, a method to automatically control detection gain of said pixel photodetectors, the method comprising the following steps:

• (a) identifying from a passive brightness image acquired by said TOF system which of said pixel photodetectors are receiving excessive levels of emitted optical energy to output reliable detection data, and identifying from an active brightness image which of said pixel photodetectors are receiving insufficient levels of emitted optical energy to output reliable detection data and forming a histogram of such identification;
• (b) using identification information from step (a) to traverse said active brightness image and said passive brightness image to determine therefrom number of said pixel photodetectors receiving insufficient levels of emitted optical energy, and number of said pixel photodetectors receiving neither excessive nor insufficient levels of emitted optical energy;
• (c) estimating variation in at least one system parameter of said TOF system to produce a change in light ΔL that increases said number of said pixel photodetectors receiving neither excessive nor insufficient levels of emitted optical energy;
• and
• (d) varying at least one system parameter of said TOF system to increase said number of said pixel photodetectors receiving neither excessive nor insufficient levels of emitted optical energy.

For use with a time-of-flight (TOF) system that illuminates a target, a distance z from said TOF system, with optical energy having a modulated periodic waveform that includes a high frequency component, and that detects a fraction of said illumination with an array of pixel photodetectors operable in at least two phases to determine data proportional to said distance z, said TOF system operable independently of reflectivity of said target, a control system to automatically control detection gain of said pixel photodetectors, the control system comprising:

• means for identifying from a passive brightness image acquired by said TOF system which of said pixel photodetectors are receiving excessive levels of emitted optical energy to output reliable detection data, and identifying from an active brightness image which of said pixel photodetectors are receiving insufficient levels of emitted optical energy to output reliable detection data and forming a histogram of such identification;
• means for traversing said active brightness image and said passive brightness image and for determining therefrom number of said pixel photodetectors receiving insufficient levels of emitted optical energy, and number of said pixel photodetectors receiving neither excessive nor insufficient levels of emitted optical energy;
• means for estimating variation in at least one system parameter of said TOF system to produce a change in light ΔL that increases said number of said pixel photodetectors receiving neither excessive nor insufficient levels of emitted optical energy;
• and
• means for varying at least one system parameter of said TOF system to increase said number of said pixel photodetectors receiving neither excessive nor insufficient levels of emitted optical energy.