Method and system for estimating exposure time of a multispectral light source

A method for estimating an exposure parameter value for imaging an object with an imaging device comprising a plurality of solid state light sources arranged into at least one first group and at least one second group, the first and second light source groups emitting light within wavelength bands wherein the total coverage of all wavelength bands of a first light source group is at least as wide or wider as any wavelength band of a second light source group, an image sensor having digital sensor values adopting a level of saturation, an image processor receiving the digital sensor values and carrying out the method;

• the method comprising the steps of:
• imaging the object with the at least one first light source group with a first exposure parameter value,
• the image sensor capturing an image of the object, and
• mapping the image onto the digital sensor values,
• and the image processor estimating a second exposure parameter value for the at least one second light source group from the digital sensor values,
• and extracting at least one percentile of the digital sensor values,
• and estimating the second exposure parameter value as a function of the first exposure parameter value and of a constant,
• and of device calibration data,
• and of a target level of saturation of the image sensor,
• and of a first black level,
• and of the measured digital sensor values of that least one first light source group,
• and of a second black level,
• wherein the device calibration data comprises the relationship between the digital sensor values and the sensor exposure parameter value for a reference object.

A system for estimating an exposure parameter value for imaging an object with an imaging device comprising:

• a plurality of solid state light sources arranged into at least a first light source group and at least a second light source group, the light source groups emitting light within wavelength bands wherein the total coverage of all wavelength bands of the first light source group is at least as wide or wider as any wavelength band of the second light source group, an image sensor having digital sensor values adopting a level of saturation,
• an image processor receiving the digital sensor values and the system is configured to implement the steps of:
• imaging the object with at least the first light source group with a first exposure parameter value,
• the image sensor capturing an image of the object, and
• mapping the image onto the digital sensor values,
• and the image processor estimating a second exposure parameter value for at least the second light source group from the digital sensor values,
• and extracting at least one percentile of the digital sensor values,
• and estimating the second exposure parameter value as a function of the first exposure parameter value and of a constant
• and of device calibration data,
• and of a target level of saturation of the image sensor,
• and of a first black level,
• and of the measured digital sensor values of at least the first light source group,
• and of a second black level,
• wherein the device calibration data comprises the relationship between the digital sensor values and the sensor exposure parameter value for a reference object.

A controller for estimating an exposure parameter value for imaging an object with an imaging device, said imaging device comprising:

• a plurality of solid state light sources arranged into at least one first group and at least one second group, the first and second light source groups emitting light within wavelength bands wherein the total coverage of all wavelength bands of a first light source group is at least as wide or wider as any wavelength band of a second light source group, and
• an image sensor having digital sensor values adopting a level of saturation,
• the controller comprising:
• an image processor receiving the digital sensor values and being adapted to carry out the steps of:
• imaging the object with the at least one first light source group with a first exposure parameter value,
• the image sensor capturing an image of the object, and
• mapping the image onto the digital sensor values,
• and the image processor estimating a second exposure parameter value for the at least one second light source group from the digital sensor values,
• and extracting at least one percentile of the digital sensor values,
• and estimating the second exposure parameter value as a function of the first exposure parameter value and of a constant,
• and of device calibration data,
• and of a target level of saturation of the image sensor,
• and of a first black level,
• and of the measured digital sensor values of that least one first light source group,
• and of a second black level,
• wherein the device calibration data comprises the relationship between the digital sensor values and the sensor exposure parameter value for a reference object.