Printer calibration using limited range reflection scanners as input sources
A method of calibrating a printer using a reflective scanner is disclosed. Because the reflective scanner used for calibration may only be able to accurately measure a limited density range that is less than the full density range of the printer, some information from the reflective scanner is disregarded or deemphasized during the calibration process. A calibration page is printed and scanned. Lookup tables (LUTs) that comprise the printer calibration values are updated based on adjustments calculated from the scanner for density regions where the scanner produces relatively accurate measurements, but updated based on the preexisting settings for density regions where the scanner produces relatively inaccurate measurements. In transitions regions between accurate and inaccurate regions, the LUTs are adjusted based on a combination of measurements from the scanner and the preexisting settings.
1. A method of characterizing a limited range reflective color scanner for use as a calibration input source, comprising:
a) selecting a type and model of scanner to be characterized;
b) using a measurement instrument to read a test target comprising a plurality of printed patches;
c) using the scanner to read the plurality of printed patches on the test target;
d) converting scan data obtained from the scanner reading the plurality of printed patches on the test target to a form compatible with data obtained from the measurement instrument;
e) using a processor to compare the converted scan data with the data obtained from the measurement instrument;
f) using the processor to calculate a weighting from the comparison for use by a calibration algorithm;
g) using the calibration algorithm to update a lookup table, wherein the update weighs more heavily scan data that corresponds to accurate ranges for the selected type and model of the scanner and disregards scan data that corresponds to inaccurate ranges for the selected type and model of the scanner; and
h) modifying printing parameters using the updated lookup table.
2. The method of claim 1 wherein the printing parameters are used to optimize a printed output of a printer.
3. The method of claim 1 wherein selecting the type and model of scanner to be characterized comprises:
selecting multiple scanners to be characterized; and
averaging scan data from the multiple scanners.
4. The method of claim 1 wherein scan data from the scanner is converted to Status A Densities, DIN Densities, or Channel Independent Densities based on the associated densitometer or spectrophotometer readings.
5. The method of claim 1 wherein the accurate and inaccurate ranges for the selected type and model of scanner are limited by flare, platen glass contamination, electronic noise, clipping, or a voltage offset on a CCD.
6. The method of claim 1 wherein the accurate ranges for the selected type and model of the scanner is smaller than an output range of a chosen printer.
7. The method of claim 1 wherein the modified printing parameters are configured for printer types comprising electrophotographic, thermal dye diffusion, inkjet, or digital photographic printer types.
8. The method of claim 1 wherein the updated lookup table and modified printing parameters are used to produce a printed output that is calibrated in critical locations of human eye sensitivity.
9. The method of claim 8 wherein the printed output is provided by a printer separate from the scanner.