Methods and apparatuses for printer recalibration
A test pattern printed by a printer is assessed—without colorimetric equipment—to provide data used in recalibrating the printer. The assessment may be made by an unskilled operator, and can include discerning whether a particular pattern is visible in the printed test pattern, or whether a feature in the test pattern is relatively wider or narrower. From such assessment, needed changes to the printer's calibration data are inferred and implemented. A variety of other printer calibration techniques are disclosed. The technology is illustrated in the context of dye sublimation printers, and is particularly useful in optimizing printing of digitally-watermarked graphics.
1. A method for changing a tonal compensation parameter of a printer without resort to colorimetric measurement, said method comprising:
instructing the printer to print a test graphic comprised of elements that should differ slightly in tone value;
receiving data based on an assessment of the appearance of the test graphic as actually printed; and
by reference to said received data, changing a tonal compensation parameter of the printer;
wherein the method includes instructing the printer to print a graphic having a region of linearly varying tone, comprising at least three consecutive sub-regions, each corresponding to a different input signal value; and
receiving data related to a non-linearity in the tonal variation as actually printed.
2. A method for changing a tonal compensation parameter of a printer without resort to colorimetric measurement, said method comprising:
instructing the printer to print a test graphic comprised of elements that should differ slightly in tone value;
receiving data based on an assessment of the appearance of the test graphic as actually printed; and
by reference to said received data, changing a tonal compensation parameter of the printer;
wherein the method includes instructing the printer to print a graphic in which the tone is changed there across in uniform steps, the printer responding to said instruction by printing at least one portion of uniform tone there across despite said instructed steps in value; and
receiving data related to a dimension of said portion of uniform tone.
3. The method of claim 2 that includes changing a tonal compensation parameter in a first way if the dimension is relatively larger, and changing the tonal compensation parameter in a second, opposite, way if the dimension is relatively smaller.
4. A method for changing a tonal compensation parameter of a printer without resort to colorimetric measurement, said method comprising:
printing a test pattern that, in a properly compensated printer, would comprise a sequence of at least three immediately adjoining patches of different print tones, the tone of the second patch being midway between the tones of the first and third patches;
determining a number of differently-toned patches printed in said test pattern; and
by reference to said determining, initiating a change in a tonal compensation parameter of the printer.
5. A method for changing a tonal compensation parameter of a printer without resort to colorimetric measurement, said method comprising:
instructing the printer to print a test graphic comprised of different elements;
receiving data based on an assessment of the appearance of the test graphic, as actually printed; and
by reference to said received data, changing a tonal compensation parameter of the printer;
wherein first and second elements are printed with first and second different input signal values for which the printer should output the same tonal value; and
if the received data indicates that the first and second elements, as printed, have different tonal values, then decreasing contrast of the printer in part of its operating range.
6. The method of claim 5 that also includes increasing a contrast of the printer in a different part of its operating range.