EXTENDING DYNAMIC RANGE OF STORED IMAGE DATABASE

摘要

The dynamic range of a digitized image database is extended to permit shifting of encoded pixel values without 'clipping', and to provide limited windows of values into which specular highlights and unusually low reflectances or areas of objects in shadow light may be encoded and stored. Digital codes into which an image scanner output has been mapped by a scene balance mechanism are converted into a set of reduced-range digital codes of the same resolution but having a smaller range of basic image content values than the dynamic range of the digitized image data base. The code conversion mechanism operates to convert a maximum value of 100% white reflectance to an encoded value that is less than the upper limit of the dynamic range of the database to allow for the placement of specular highlights that are beyond the 100% diffuse white reflectance maximum, to convert a defined minimum value of low reflectance to an encoded value that is greater than the lower limit of the dynamic range of the database to allow for the placement of unusually low reflectances or areas of objects in shadow light, and to accommodate shifts in the digitized imagery data at both the high and low ends of the range.