Image contrast enhancement technique

Claim 2

An image contrast enhancement technique for adjusting the intensity of an image of a scene, said image being realized from electrical signals generated in response to radiation received from a plurality of regions within a field of view of said scene, comprising the steps of: a) filling a first matrix with a plurality of digital entries corresponding to each of said electrical signals, said plurality of digital entries having a maximum and a minimum value with the difference between the maximum and minimum digital entries defining a first dynamic range; b) sampling said first matrix to create a first sample set of said plurality of digital entries, said sample set having a second dynamic range substantially similar to said first dynamic range; c) constructing a histogram of said first sample set of digital entries; d) at least approximating the integral of said histogram to generate a first transfer function, said first transfer function having a value at each of said plurality of digital entries of said first matrix; e) generating a second matrix having a plurality of digital entries obtained by multiplying each of said plurality of digital entries of said first matrix by the value of said first transfer function at each of said entries; and f) generating said image by driving a display with signals derived from said plurality of digital entries of said second matrix.

Claim 3

The technique of claim 1 further including the step of scaling said first transfer function.

Claim 4

The technique of claim 1 wherein said step of sampling said first matrix includes the step of collecting said entries from alternate rows of said first matrix.

Claim 5

The technique of claim 3 wherein said step of sampling said first matrix further includes the step of collecting said entries from every Nth column of said first matrix, where the number of said columns is evenly divisible by N.

Claim 6

The technique of claim 1 wherein said step of at least approximately integrating said histogram further includes the step of adding a bin bias constant to each of said plurality of digital entries to reduce the contrast of said image.

Claim 7

The technique of claim 1 wherein said step of at least approximately integrating said histogram further includes the steps of: a) summing the values of said histogram from a first sequential subset of said first sample set of digital entries to accumulate a first sum and assigning said first sum to be the value of said approximated integral at the largest digital entry within said first subset; b) summing the values of said histogram from a second sequential subset of said first sample set of digital entries to accumulate a second sum, said second subset being adjacent to said first subset on an axis of said histogram, and temporarily assigning said second sum to be the value of said approximated integral at the largest digital entry within said second subset; c) summing said first and second sums to form a third sum; d) assigning said third sum to be the value of said approximated integral at the largest digital entry within said second subset; and e) approximating the value of said histogram integral over said second subset by interpolating between said first and third sums.

Claim 8

The technique of claim 1 further including the steps of: a) storing the maximum value of said first transfer function; b) updating said first matrix with a plurality of digital entries from a second scene to be imaged; c) sampling said updated first matrix to create a second sample set of said digital entries; d) constructing a second histogram of said second sample set of digital entries; e) at least approximately integrating said second histogram to generate a second transfer function, said second transfer function having a value at each entry from said second scene; f) updating said second matrix by multiplying each of the entries of said updated first matrix by both the value of said second transfer function at each of said entries of said updated first matrix and by a scale factor proportional to the quotient of the maximum signal value accepted by said display and said stored maximum value of said first transfer function; and h) updating said image by driving said display with said updated second matrix.

Claim 9

The technique of claim 1 wherein said step of at least approximately integrating said histogram is performed by integrating over the largest to the smallest of said plurality of digital entries.

Claim 10

An image contrast enhancement technique for adjusting the intensity of an image of a scene, said image being realized from electrical signals generated in response to radiation received from a plurality of regions within a field of view of said scene, comprising the steps of: a) filling a first matrix with a first plurality of digital entries corresponding to each of said electrical signals, said first plurality of digital entries being sampled and having a maximum and a minimum value with the difference between the maximum and minimum digital entries defining a first dynamic range over said field of view of said scene; b) refilling said first matrix with a second plurality of digital entries from said scene and resampling said first matrix to create a sample set of digital entries from said second plurality of digital entries, said sample set having a second dynamic range substantially similar to said first dynamic range; c) constructing a histogram of said sample set of digital entries; d) at least approximating the integral of said histogram to generate a first transfer function, said first transfer function having a value at each of said second plurality of digital entries of said first matrix; e) generating a second matrix having a third plurality of digital entries obtained by multiplying each of said second plurality of digital entries of said first matrix by the value of said first transfer function at each of said second plurality of digital entries; and f) generating said image by driving a display with signals derived from said third plurality of digital entries of said second matrix.

Claim 11

An image contrast enhancement technique for adjusting the intensity of an image of a scene, said image being realized from electrical signals generated in response to radiation received from a plurality of regions within a field of view of said scene, comprising the steps of: a) filling a first matrix with a first plurality of digital entries corresponding to each of said electrical signals, said first plurality of digital entries being sampled and having a maximum and a minimum value with the difference between the maximum and minimum digital entries defining a first dynamic range over said field of view of said scene; b) refilling said first matrix with a second plurality of digital entries from said scene and resampling said first matrix to create a sample set of digital entries from said second plurality of digital entries, said sample set having a second dynamic range substantially similar to said first dynamic range; c) constructing a histogram of said sample set of digital entries; d) at least approximating the integral of said histogram to generate a first transfer function, said first transfer function having a value at each of said second plurality of digital entries of said first matrix; e) generating a second matrix having a third plurality of digital entries obtained by multiplying each of said second plurality of digital entries of said first matrix by the value of said first transfer function at each of said second plurality of digital entries; and f) generating said image by driving a display with signals derived from said third plurality of digital entries of said second matrix.