System and method for generating a contrast overlay as a focus assist for an imaging device

An apparatus for generating a contrast false color overlay as a focus assist from an input signal, the apparatus comprising:

• a divider having an input and a plurality of outputs, for dividing the input signal into a plurality of output signals, the input of the divider coupled to receive the input signal;
• a combiner having a plurality of inputs and an output for combining a plurality of signals into a single signal;
• and
• a signal reducer having a plurality of inputs and at least a first output and a second output, each of the plurality of inputs coupled to a corresponding one of the plurality of outputs of the divider, the signal reducer decreasing the amplitude of each divided input signal by a predetermined amount, the second output of the signal reducer coupled to one of the plurality of inputs of the combiner;
• an automatic gain control unit having an input and an output, for producing a contrast signal whose amplitude is proportional to the contrast in an image, the automatic gain control unit coupled to receive one of the plurality of output signals by coupling the input of the automatic gain control unit to one of the plurality of outputs of the divider, and
• an adder having a first input, a second input and an output for summing two signals, the first input of the adder coupled to the first output of the signal reducer, the second input of the adder coupled to the output of the automatic gain control unit, and the output of the adder coupled to one of the plurality of inputs of the combiner.

An apparatus for generating a contrast false color overlay as a focus assist from an input signal, the apparatus comprising:

• a high pass filter having an input and an output, for differentiating a signal to extract high frequency components and produce a contrast signal, the input of the high pass filter coupled to receive the input signal;
• an AGC circuit having an input and an output, for limiting the gain of the contrast signal, the input of the AGC circuit coupled to the output of the high pass filter;
• a gain control circuit having an input and an output, for reducing the amplitude of the input signal, the input of the gain control circuit coupled to receive the input signal;
• and
• an adder having an first input, a second input and an output, for summing signals applied to the first and second inputs, the first input of the adder coupled to the output of the AGC circuit, the second input of the adder coupled to the output of the gain control circuit.

A method for displaying a false color contrast overlay as a focus assist on an output device, the method comprising the steps of:

• receiving an input signal representing an image;
• separating the input signal into channel signals;
• receiving a luminance signal;
• producing, from the luminance signal, a contrast signal with an amplitude that varies with contrast in the image;
• reducing the contrast signal;
• reducing the channel signals;
• combining the reduced contrast signal with the reduced channel signals to produce a combined signal;
• and
• generating the image on the output device using the combined signal.

A method for displaying a false color contrast overlay as a focus assist on an output device, the method comprising the steps of:

• receiving an input signal representing an image;
• separating the input signal into channel signals;
• generating a luminance signal;
• producing, from the luminance signal, a contrast signal with an amplitude that varies with contrast in the image;
• reducing the contrast signal;
• reducing the channel signals;
• combining the reduced contrast signal with the reduced channel signals to produce a combined signal;
• and
• generating the image on the output device using the combined signal.