Calibration techniques for imaging devices

Abstract

The invention is directed to various calibration techniques for calibrating an imagining device such as a display device, a printer, or a scanner. The techniques may involve characterizing the imaging device with a device model such that an average error between expected outputs determined from the device model and measured outputs of the imaging device is on the order of an expected error, and adjusting image rendering on the imaging device to achieve a target behavior. The invention can achieve a balance between analytical behavior of the imaging device and measured output. In this manner, adjustments to image rendering may be more likely to improve color accuracy and less likely to overcompensate for errors that are expected.

1 . A method for calibrating a display device, the method comprising:
 identifying a plurality of device-dependent color coordinates intended to produce a plurality of neutral colors;   reproducing a plurality of colors on the display device for the plurality of device-independent color coordinates;   measuring a plurality of device-independent color coordinates for the plurality of reproduced colors;   identifying a plurality of target device-independent color coordinates corresponding to at least some of the plurality of neutral colors; and   determining adjustments to a device-dependent color coordinate LUT wherein the adjustments are designed to reduce differences between the measured and target device-independent coordinates to within a range of expected measurement errors and wherein determining comprises determining without measuring additional color coordinates.   
   
   
       2 . A method according to  claim 1  wherein the range of expected measurement errors comprise an average color error of 0.3 delta E or less. 
   
   
       3 . A method according to  claim 1  wherein the range of expected measurement errors comprise a maximum color error of 0.6 delta E or less. 
   
   
       4 . A method according to  claim 1  wherein identifying the plurality of target device-independent color coordinates corresponding to the plurality of neutral colors comprises:
 characterizing the display device with a device model; and   identifying coordinates using the device model.   
   
   
       5 . A method according to  claim 4  wherein characterizing the display device with a device model comprises determining values for a plurality of adjustable parameters of the device model. 
   
   
       6 . A method according to  claim 1  wherein identifying the plurality of target device-independent color coordinates corresponding to the plurality of neutral colors comprises pre-determined color coordinates. 
   
   
       7 . A computer readable medium storing program code that when executed calibrates a display device by:
 identifying a plurality of device-dependent color coordinates intended to produce a plurality of neutral colors;   reproducing a plurality of colors on the display device for the plurality of device-independent color coordinates;   measuring a plurality of device-independent color coordinates for the plurality of reproduced colors;   identifying a plurality of target device-independent color coordinates corresponding to at least some of the plurality of neutral colors; and   determining adjustments to a device-dependent color coordinate LUT wherein the adjustments are designed to reduce differences between the measured and target device-independent coordinates to within a range of expected measurement errors and wherein determining comprises determining without measuring additional color coordinates.   
   
   
       8 . A computerized apparatus for calibrating a display device, comprising:
 a measurement device operative to supply a device-independent color coordinate for a color reproduced by the display device; and   a calibration module operative to:
 identify a plurality of device-dependent color coordinates intended to produce a plurality of neutral colors; 
 supply the plurality of device-dependent color coordinates to the display device to display the intended neutral colors; 
 obtain device-independent color coordinates for the intended neutral colors from the measurement device; 
 identify a plurality of target device-independent color coordinates corresponding to at least some of the intended neutral colors; and 
 determine adjustments to a device-dependent color coordinate LUT wherein the adjustments are designed to reduce the difference between the measured and target device-independent coordinates to within the range of expected measurement errors and wherein the calibration module determines adjustments without measuring additional color coordinates.