Patent Document ID: 5450502
Application ID: 08133231
Patent Status: 1

Claim One:
1. A method of improving the contrast in a natural scene image recorded as a set of electronic signals, including the steps of: assuring that at least one component of the original electronic signal forming the natural scene image is defined with a signal describing intensity of the image; from an intensity term of the electronic signals, deriving a histogram signal, describing the population of signals at each possible intensity level within the image, including the substeps of: from the intensity signals, generating a global histogram signal, describing the population of intensity signals at each possible intensity level; comparing the global histogram signal to a reference-flat signal; and deriving a global variance from the comparison, representing the flatness of the histogram signal, from the intensity signals, dividing the image into a plurality of discrete areas; for each discrete area of the image, generating a local histogram signal, describing the population of intensity signals at each possible intensity level therewithin; comparing each local histogram to a reference-flat signal, and deriving a local variance from the comparison, representing the flatness of the local histogram; comparing each local variance to the global variance to determine whether the local histogram has a variance smaller than the adjusted global variance; if at least a preset number of local variances are less than the adjusted global variance, forming a weighted sum of the local histogram signals having a variance less than the adjusted global variance value and obtaining a relevant histogram signal; operating on the relevant histogram signal with a filter that has the characteristics of reducing strong peaks and valleys in the signal; using the filtered histogram signal, deriving a tonal mapping of input signals to printer driver signals; for each electronic signal forming the natural scene image mapping the electronic signal to an output driver signal, using the tonal mapping derived.