Browse Prior Art Database

Non-linear Color Quantization on High Definition Displays

IP.com Disclosure Number: IPCOM000121267D
Original Publication Date: 1991-Aug-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 2 page(s) / 75K

Publishing Venue

IBM

Related People

Todd, S: AUTHOR

Abstract

Displays such as the 6090 use a frame buffer of 8 bits each red, green and blue (rgb) color. If the 256 values for each color are used to represent linear intensity steps, the edges between dark bands are clearly visible as a band of 1/255 and 2/255. Disclosed is a method that overcomes these intensity steps by the use of non-linear quantization of rendered values in the frame buffer. The method can also apply to audio compact disks by replacing the enhancement of 14 bits to 16 bits with non-linear mapping.

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Non-linear Color Quantization on High Definition Displays

      Displays such as the 6090 use a frame buffer of 8 bits
each red, green and blue (rgb) color.  If the 256 values for each
color are used to represent linear intensity steps, the edges between
dark bands are clearly visible as a band of 1/255 and 2/255.
Disclosed is a method that overcomes these intensity steps by the use
of non-linear quantization of rendered values in the frame buffer.
The method can also apply to audio compact disks by replacing the
enhancement of 14 bits to 16 bits with non-linear mapping.

      With the current architecture, the only way to accurately
display the result of rendering is to store an inverse gamma map in
the display color table.  If a smooth dark intensity ramp is
displayed, the steps between the levels 0, 1/255, 2/255 and so on are
very clearly visible.

      A simplified version of the back end of the 6090 pipeline is as
below, repeated for each color.
                                  digital      photons
        rendering  ->  frame  ->  display  ->    off
                       buffer     signal       screen

      The step from rendering to the frame buffer is the color
quantization.  The step from the frame buffer to digital signal uses
the display color table.  The final step from digital display to
photons involves the digital-to-analog converter, analog drivers and
tube. Several issues relate to the quality of the final image
compared to the quality of the data produced by the renderer.
-    The step from the digital display signal to the photons is non-
linear, distorted by the gamma curve.
-    Human perception of the difference between two true intensity
levels is a non-linear process.
-    The values produced by the render should relate in a linear
manner to the photons emitted.
-    The current implementation of the quantization step from
re...