| Popis: |
As printing proceeds in a thermal printer, heat from previously printed lines of image data accumulates in the print head and alters the thermal state of the heating elements. This fluctuating state of the heating elements manifests itself as a distortion in the printed image. We have modeled the heat diffusion within the thermal printer and the density response of the receiver medium to derive a computationally efficient inverse thermal printer model. In this model, the heat diffusion problem for the moving receiver is simplified by showing that it is equivalent to a stationary medium with lower conductivity. The thermal print head is modeled as having a finite number of discrete layers with differing time constants. The layer temperature updates can be decoupled and are time recursive if expressed in relative rather than absolute temperatures, and this decoupling allows the layers to be updated at multiple spatial and temporal resolutions. The inverse printer model then reduces to an elegant algorithm that comprises three interleaved recursions; namely, absolute temperature propagation from coarse-to-fine scale, energy propagation from fine-to-coarse scale and relative temperature update in time. Experimental results demonstrate that the proposed algorithm successfully corrects the distortion produced by thermal printers. |
