Electrophotographic printing with compensation

A method of printing an image on a receiver using an electrophotographic printer adapted to deposit toner in a plurality of columns on the receiver, the method comprising:

• printing a test target having a plurality of densities in each column on a first receiver;
• receiving measurements of the test target on the receiver to provide a respective column tonescale for each column;
• determining a plurality of aim tonescales;
• selecting one of the aim tonescales for each column and computing a respective column-tonescale gain for each column so that the respective first product of each column-tonescale gain and its respective column tonescale approximates the selected aim tonescale within a selected tolerance;
• receiving a plurality of input pixel values, and, for each pixel value:
• computing an adjusted pixel value by multiplying the value of the selected aim tonescale at the pixel value by the column-tonescale gain for the corresponding column;
• and
• exposing the photoreceptor in a respective pixel area to light corresponding to the adjusted pixel value;
• applying toner to the photoreceptor to form thereon a visible image corresponding to the exposure of the photoreceptor;
• and
• transferring the visible image to a second receiver so that a print corrected for nonuniformity is produced.

A method of producing calibration data for an electrophotographic printer, comprising:

• printing a test target having a plurality of densities in each column on a first receiver;
• receiving measurements of the test target on the receiver to provide a respective column tonescale for each column;
• receiving an aim tonescale and a crossover range of pixel levels;
• computing a respective column-tonescale gain for each column so that the respective first product of each column-tonescale gain and its respective column tonescale intersects the aim tonescale in the crossover range;
• determining an adjustment tonescale using the respective residual errors between the aim tonescale and each first product, wherein the adjustment tonescale changes sign within the crossover range;
• and
• computing a respective adjustment-tonescale gain for each column using the respective first product, the adjustment tonescale, and the aim tonescale.

A method of producing, on a receiver, a print compensated for nonuniformity of an electrophotographic printer, comprising:

• receiving an aim tonescale, an adjustment tonescale, and a plurality of column-tonescale gains and adjustment-tonescale gains, each gain corresponding to one column;
• receiving a plurality of input pixel values, and, for each pixel value:
• computing a first adjustment by multiplying the value of the aim tonescale at the pixel value by the column-tonescale gain for the corresponding column;
• computing a second adjustment by multiplying the value of the adjustment tonescale at the pixel value by the adjustment-tonescale gain for the corresponding column;
• exposing the photoreceptor in a respective pixel area to light corresponding to the first and second adjustments;
• applying toner to the photoreceptor to form thereon a visible image corresponding to the exposure of the photoreceptor;
• and
• transferring the visible image to a second receiver so that a print corrected for nonuniformity is produced.