We describe and implement an algorithmic framework for memory
efficient, 'on-the-fly' halftoning in a progressive transmission
environment. Instead of a conventional approach which repeatedly
recalls the continuous tone image from memory and subsequently
halftones it for display, the proposed method achieves significant
memory efficiency by storing only the halftoned image and updating
it in response to additional information received through
progressive transmission. Thus the method requires only a single
frame-buffer of bits for storage of the displayed binary image and
no additional storage is required for the contone data. The
additional image data received through progressive transmission is
accommodated through in-place updates of the buffer. The method is
thus particularly advantageous for high resolution bi-level
displays where it can result in significant savings in memory.
The proposed framework is implemented using a suitable
multi-resolution, multi-level modification of error diffusion that
is motivated by the presence of a single binary frame-buffer.
Aggregates of individual display bits constitute the multiple
output levels at a given resolution. This creates a natural
progression of increasing resolution with decreasing bit-depth.