Browse Prior Art Database

Partial Dot Overlap Method for Grey Scale Printing

IP.com Disclosure Number: IPCOM000103897D
Original Publication Date: 1993-Feb-01
Included in the Prior Art Database: 2005-Mar-18
Document File: 4 page(s) / 100K

Publishing Venue

IBM

Related People

Just, D: AUTHOR [+2]

Abstract

Disclosed is an improved method for generating high-quality grey-scale images (either monochrome or full-color) using conventional drop-on-demand thermal ink-jet, or similar means, by employing controlled partial dot overlap of multiple ink densities to provide a very large increase in the number of achievable grey scales. The basic concept can also be extended to other printing technologies. In general, a binary printer producing a super-pixel of N total pixels can generate (N+1) effective grey-levels for a given color at the super-pixel resolution. Alternately, some number, K, of different dye densities can be used in the same super-pixel arrangement to generate (K*N+1) effective grey levels [1].

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Partial Dot Overlap Method for Grey Scale Printing

      Disclosed is an improved method for generating high-quality
grey-scale images (either monochrome or full-color) using
conventional drop-on-demand thermal ink-jet, or similar means, by
employing controlled partial dot overlap of multiple ink densities to
provide a very large increase in the number of achievable grey
scales.  The basic concept can also be extended to other printing
technologies.  In general, a binary printer producing a super-pixel
of N total pixels can generate (N+1) effective grey-levels for a
given color at the super-pixel resolution.  Alternately, some number,
K, of different dye densities can be used in the same super-pixel
arrangement to generate (K*N+1) effective grey levels [1].  This
approach was extended to include the case of completely overlapping
dots, which significantly increases the number of grey levels [2].

      This disclosure extends and improves upon these approaches by
describing the case where the K different dye densities can be
printed in conventional fixed-size dots, but where the printed dots
can also take a relatively  small number of intermediate positions
between the normal dot positions.  By permitting the printing of dots
at intermediate positions, controlled overlap of nearby printed dots
is achieved which provides a tremendous amplifying effect on the
number of achievable grey levels.  Furthermore, the uniformity of the
resulting optical density steps is greatly enhanced, because the
partial overlap allows a nearly continuous change of the optical
density, even for minimal super-pixel sizes.  The concept is
described for the relatively simple case of a 2x2 super-pixel and two
ink densities.  Partial dot overlap is provided by horizontally
addressing dot positions between the 'normal' pixel positions.  (Such
horizontal shifts are easily produced on typical serial printers).
The radius of the printed dot is assumed to be identical with the
diagonal of a pixel cell.  Fig. 1 shows a sketch of a superpixel with
the accessible positions for the dot labeled A0, A1, A2, A3, A4.
Only three additional positions have been permitted between the
regular printing pixel positions.  Also, only horizontal shifts
towards the center of the super-pixel are considered to reduce the
effect of overlapping dots from neighboring superpixels.
Furthermore, in this simplified example, only two pixels are
permitted to be printed by each nozzle on each row of a single
super-pix...