Method and device for calibrating an imaging apparatus

A method for calibrating a halftone imaging system having a radiation source for exposing an imaging element, the method comprising the steps of:

• forming a plurality of image regions on an imaging element with the radiation source such that each image region is defined by at least one corresponding halftone cell, wherein the halftone cells of different image regions have an equal target dot area and are exposed by the radiation source at different exposure levels, wherein the forming step includes the step of selecting the different exposure levels based on a predetermined parameterization of a sensitometric curve for the imaging element in order to form a reduced number of image regions;
• measuring a corresponding density for each image region;
• and
• setting an optimum exposure level for the halftone imaging system as a function of the measured densities for the image regions.

A method for calibrating a halftone imaging system having a radiation source for exposing an imaging element, the method comprising the steps of:

• forming a first plurality of image regions on an imaging element with the radiation source, wherein each image region of the first plurality of image regions is defined by at least one corresponding halftone cell having a plurality of dots, and further wherein the dots of the halftone cells of different image regions have an equal target dot area and are exposed by the radiation source at different exposure levels;
• setting an optimum exposure level for the imaging system based on a comparison between the target dot area and an actual dot area for each respective image region of the first plurality of image regions;
• forming a second plurality of image regions on the element such that each image region of the second plurality of image regions is defined by at least one corresponding halftone cell having a plurality of dots, wherein the halftone cells of different image regions of the second plurality of image regions have different target dot areas and are exposed by the radiation source at the optimal exposure level;
• and
• developing a linearization mechanism for mapping subsequent target dot areas to respective actual dot areas based on a comparison between the target dot area and an actual dot area for each respective image region of the second plurality of image regions.

An apparatus for calibrating a halftone imaging system comprising:

• a radiation source for exposing an imaging element;
• a densitometer for measuring a density of the imaging element;
• and
• a controller coupled to the radiation source and the densitometer, the controller adapted to perform the steps of:
• (i) controlling the radiation source to form a first plurality of image regions on an imaging element such that each image region of the first plurality of image regions is defined by at least one corresponding halftone cell having a plurality of dots, wherein the dots of the halftone cells of different image regions have an equal target dot area and are exposed by the radiation source at different exposure levels;
• (ii) controlling the densitometer to measure a corresponding density for each image region of the first plurality of image regions;
• (iii) controlling the densitometer to measure a minimum density for a non-imaged area of the imaging element;
• (iv) calculating an actual dot area for each image region of the first plurality of image regions as a function of the measured density of each image region of the first plurality of image regions and the measured minimum density;
• (v) setting an optimum exposure level for the imaging system based on a comparison between the target dot area and the calculated actual dot area for each image region of the first plurality of image regions;
• (vi) controlling the radiation source to form a second plurality of image regions on the imaging element such that each image region of the second plurality of image regions is defined by at least one corresponding halftone cell having a plurality of dots, wherein the halftone cells of different image regions of the second plurality of image regions have different target dot areas and are exposed by the radiation source at the determined optimal exposure level;
• (vii) measuring a corresponding density for each image region of the second plurality of image regions;
• (viii) calculating an actual dot area for each of the image regions of the second plurality of image regions as a function of the measured density of each image region of the second plurality of image regions and the measured minimum density;
• (ix) calculating an error between the target dot area for each of the image regions of the second plurality of image regions and the respective actual dot area;
• and
• (x) developing a linearization mechanism for mapping subsequent target dot areas to respective actual dot areas based on the calculated error.

A halftone imaging system for forming a calibrated output image on an output media according to a page description language, the halftone imaging system comprising:

• a recorder comprising:
• a radiation source for exposing an imaging element;
• a densitometer for measuring a density of the imaging element;
• a controller coupled to the radiation source and the densitometer, the controller adapted to perform the steps of:
• (i) controlling the radiation source to form a first plurality of image regions on an imaging element such that each image region of the first plurality of image regions is defined by at least one corresponding halftone cell having a plurality of dots, wherein the dots of the halftone cells of different image regions have an equal target dot area and are exposed by the radiation source at different exposure levels,
• (ii) controlling the densitometer in order to determine an optimum exposure level for the imaging system based on a comparison between the target dot area and an actual dot area for each image region of the first plurality of image regions,
• (iii) controlling the radiation source to form a second plurality of image regions on the element such that each image region of the second plurality of image regions is defined by at least one corresponding halftone cell having a plurality of dots, wherein the halftone cells of different image regions of the second plurality of image regions have different target dot areas and are exposed by the radiation source at the determined optimal exposure level, and
• (iv) controlling the densitometer in order to develop a linearization mechanism for mapping subsequent target dot areas to respective actual dot areas;
• and
• a raster image processor for receiving image data characterized by a page description language and providing raster data to the recorder based on the image data, wherein the recorder communicates the linearization mechanism to the raster image processor for mapping target dot areas to target dot areas while processing the page description language.