Method for generating real time degree of focus signal for handheld imaging device
First Claim
1. A method for determining the degree of focus in an optical reader of the type including an image sensor for generating an electrical signal including a plurality of data elements which together define an image of a target object projected thereon, a data memory for storing the gray scale values of the data elements of said image in a suitable address space, and a control circuit for controlling said image sensor and said data memory, including the steps of:
- (a) selecting, from said address space, a set of sampling addresses for use in sampling said gray scale values;
(b) determining, for a plurality of pairs of proximately located ones of said set of sampling addresses, the gray scale values stored at said pairs of sampling addresses;
(c) deriving, from the gray scale values stored at said pairs of sampling addresses, a focus metric signal indicative of the sharpness of the image on said image sensor; and
(d) using said focus metric signal to generate, substantially in real time, an output signal having a user perceptible property that varies in accordance with said focus metric signal.
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Abstract
A method for generating, substantially in real time, a user perceptible indication of the degree to which the distance between a handheld imaging device and a target object approximates the in-focus distance therebetween. A stored image of the target object is sampled, in accordance with a pattern of sampling addresses, to determine the magnitude of the slopes of the transitions of the stored image. The stored image is also sampled to determine the contrast value of the stored image. The highest magnitude slope values and the image contrast value are combined to produce a focus metric signal that is indicative of the degree to which the imaging device approximates an in-focus condition. The focus metric signal is then used to generate a user perceptible signal that can be utilized by an operator to move the imaging device toward its in-focus distance.
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Citations
50 Claims
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1. A method for determining the degree of focus in an optical reader of the type including an image sensor for generating an electrical signal including a plurality of data elements which together define an image of a target object projected thereon, a data memory for storing the gray scale values of the data elements of said image in a suitable address space, and a control circuit for controlling said image sensor and said data memory, including the steps of:
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(a) selecting, from said address space, a set of sampling addresses for use in sampling said gray scale values; (b) determining, for a plurality of pairs of proximately located ones of said set of sampling addresses, the gray scale values stored at said pairs of sampling addresses; (c) deriving, from the gray scale values stored at said pairs of sampling addresses, a focus metric signal indicative of the sharpness of the image on said image sensor; and (d) using said focus metric signal to generate, substantially in real time, an output signal having a user perceptible property that varies in accordance with said focus metric signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25)
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26. A method for determining the degree of focus in an optical reader of the type including an image sensor for generating an electrical signal including gray scale values for a plurality of pixels which together define an image of the target object projected thereon, a data memory for storing said gray scale values at respective addresses of said data memory, and a control circuit for controlling said image sensor and said data memory, including the steps of:
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(a) establishing a sampling pattern defining the addresses of predetermined ones of said pixels; (b) selecting, from among the addresses of said sampling pattern, a plurality of sampling addresses for use in sampling the transitions of said image; (c) reading from said memory the gray scale values stored at said plurality of sampling addresses; (d) determining, from gray scale values read from said plurality of sampling addresses, the approximate slopes of those transitions of said image which correspond to said sampling addresses; (e) generating from said slopes a degree of focus signal indicative of the degree to which the position of said reader approximates its in-focus distance from said target object; and (f) generating from said degree of focus signal, substantially instantaneously, a user perceptible signal for use in moving said reader toward said in-focus distance. - View Dependent Claims (27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50)
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Specification