Abstract: Techniques are disclosed for selectively dithering only a subset of a digital image. One or more ranges of digits are selected for dithering. Only those pixels having digits within the selected range(s) in the digital image are dithered. The image is printed after being selectively dithered. Digits may be selected for dithering if they have values within the range(s) of one or more non-monotonic regions of a printer transfer function. Dithering may be performed on the subset of the digital image by applying a nonlinear transformation is applied to the image and adding a dither pattern to the transformed image. The result is quantized, and the inverse of the nonlinear transformation is applied to the quantized image to produce a dithered image. The nonlinear transformation is constructed such that the effects of the dither pattern appear only in that subset of the image having digits in the selected range(s).

Abstract: A model of a thermal print head is provided that models the thermal response of thermal print head elements to the provision of energy to the print head elements over time. The amount of energy to provide to each of the print head elements during a print head cycle to produce a spot having the desired density is calculated based on: (1) the desired density to be produced by the print head element during the print head cycle, (2) the predicted temperature of the print head element at the beginning of the print head cycle, (3) the ambient printer temperature at the beginning of the print head cycle, and (4) the ambient relative humidity.