Apparatus and method for reducing imaging errors in imaging systems having an extended depth of field

An imaging system for imaging an object located in a target region, said imaging system including, in combination:

• an optical assembly having an optical axis, said optical assembly including:
• a.) aperture means for defining an aperture having a transmittance which decreases continuously as the distance from said optical axis increases, said aperture means being characterized by an aperture function;
• b.) lens means for forming an intermediate image of said object, said image having imaging errors that include at least a misfocus error that is dependent upon the distance between said lens means and said object, said lens means being characterized by a lens function;
• and
• c.) phase masking means for receiving light incident thereon and modifying the phase thereof to cause the Optical Transfer Function (OTF) of the optical assembly to be approximately invariant over a range of distances between said lens means and said object, said phase masking means being characterized by a phase function;
• image sensing means, including an array of photosensitive elements, for receiving said intermediate image and converting said image into an intermediate image signal that includes a plurality of image elements which are distorted by said imaging errors;
• a memory for storing a set of said image elements;
• and
• processing means for:
• a.) obtaining a generalized recovery function that varies in accordance with at least the inverse of the non-ideal Incoherent Optical Transfer Function (IOTF) of said optical assembly, as calculated from at least said aperture function, said lens function and said phase function, under an approximately in-focus condition;
• and
• b.) combining one of a frequency and spatial domain representation of said intermediate image signal and said generalized recovery function to produce a recovered image signal that includes a set of image elements that together define a representation of said object in which said imaging errors have been reduced.

An imaging system for imaging an object located in a target region, said imaging system including, in combination:

• an optical assembly having an optical axis, said optical assembly including:
• a.) an aperture defining element having a transmittance which decreases continuously as the distance from the center of said aperture defining element increases in at least one direction;
• b.) at least one image forming element for forming an image of said object, said image including imaging errors that include at least a misfocus error that is dependent upon the distance between said at least one image forming element and said object;
• and
• c.) at least one phase mask for receiving light incident thereon and modifying the phase thereof to cause the Optical Transfer Function (OTF) of the optical assembly to be approximately invariant over a predetermined depth of field;
• image sensing means, including an array of photosensitive elements, for receiving said image and converting said image into an intermediate image signal;
• digital signal processing means for:
• a.) obtaining a generalized recovery function having a frequency domain representation that includes the calculated ideal Incoherent OTF (IOTF) of said optical assembly, without said at least one phase mask, under an approximately in-focus condition, divided by the calculated non-ideal IOTF of said optical assembly, with said at least one phase mask, under an approximately in-focus condition;
• and
• b.) processing said intermediate image signal and said generalized recovery function to produce a final image signal which is a better representation of said object than the intermediate image signal that would be produced by said image sensing means in the absence of said at least one phase mask.

In an optical reading apparatus for reading optically encoded data from an indicia located in a target region, in combination:

• an optical assembly having an optical axis, said optical assembly including:
• a.) at least one amplitude mask for receiving and transmitting light and for modifying said light in accordance with a transmittance function characterized by a transmittance that decreases smoothly as the distance from the center of said at least one amplitude mask increases;
• b.) image forming means for forming an intermediate image of said indicia, said intermediate image including imaging errors that include at least a misfocus error that is dependent on the distance between said image forming means and said indicia;
• and
• c.) at least one phase mask for receiving light incident thereon and modifying the phase thereof as a function of distance from the center of said at least one phase mask;
• an image sensor for receiving said intermediate image and converting said image into an intermediate image signal;
• and
• digital signal processing means for:
• a.) obtaining a generalized recovery function that varies in accordance with at least the reciprocal of the calculated non-ideal Incoherent Optical Transfer Function (IOTF) of said optical assembly, under a condition of approximately optimum focus;
• and
• b.) processing one of a frequency domain and a spatial domain representation of said generalized recovery function and said intermediate image signal to produce a final image signal having a reduced quantity of those imaging errors which have been taken into account in the calculation of said calculated non-ideal IOTF.

In an optical reading apparatus for reading optically encoded data from an indicia located in a target region, in combination:

• an optical assembly having an optical axis, said optical assembly including:
• a.) aperture means for defining a soft aperture for said optical assembly, said aperture means being characterized by an aperture function;
• b.) lens means for forming an intermediate image of said indicia, said image having imaging errors that include at least a misfocus error that is dependent upon the distance between said lens means and said indicia, said lens means being characterized by a lens function;
• and
• c.) phase masking means for receiving light incident thereon and modifying the phase thereof to cause the Optical Transfer Function (OTF) of the optical assembly to remain approximately constant over a range of distances between said lens means and said indicia, said phase masking means being characterized by a phase function;
• image converting means for receiving said intermediate image and converting said image into an intermediate image signal that includes a plurality of image elements which are distorted by said imaging errors;
• memory means for storing a set of said image elements;
• and
• processing means for:
• a.) obtaining a generalized recovery flnction that varies in accordance with at least the inverse of the calculated actual Incoherent Optical Transfer Function (IOTF) of said optical assembly, including at least said aperture function, said lens function and said phase function, under an approximately in-focus condition;
• and
• b.) combining one of a frequency and a spatial domain representation of said recovery function and said set of image elements to produce a final image signal that includes image elements which have a reduced imaging error content.