Method and apparatus for selective processing of captured images
Methods and apparatus are disclosed for identifying intended response marks in an optically scanned image of a response sheet having key marks and response targets printed in the same color. Pixel darkness values assigned by a digital imaging scanner are used to locate key marks and response targets and to identify response marks. Areas of the sheet may be selectively filtered to mask the response targets. Alternatively, a color imaging scanner may be used to produce a set of color values, such as RBG values, for each pixel. Software can act as a virtual filter by using the RBG values to detect or to mask a color in the image.
1. A method of identifying intended response marks in an optically scanned image of a response sheet having key marks and response targets printed in the same color, comprising the steps of:
(a) providing a digital imaging scanner capable of capturing an image of a response sheet with RGB values assigned to each pixel corresponding to the color of that pixel,
(b) providing a response sheet having key marks and response targets printed in the same color,
(c) capturing with the scanner a digital image of the sheet with each pixel having RGB values assigned thereto,
(d) locating key marks in the captured image by processing pixels having RGB values that correspond to the color of the key marks,
(e) calculating from the location of the key marks in the image an expected location of response targets in the image,
(f) processing pixels having RGB values corresponding to any color other than the color of the target to determine whether an intended response mark was made at a response target.
2. A method as in claim 1 , wherein the response sheet has key marks and response targets printed in red.
3. A system for identifying intended response marks in an optically scanned image of a response sheet having key marks and response targets printed in the same color, comprising:
(a) a digital imaging scanner capable of capturing an image of a response sheet with RGB values assigned to each pixel corresponding to the color of that pixel,
(b) a computer-readable medium encoded with computer-executable instructions to process the RGB values that correspond to the color of the key marks to locate key marks in the captured image,
(c) computer-executable instructions to calculate from the location of the key marks in the image an expected location of response targets in the image, and
(d) computer-executable instructions to process the RGB values that correspond to any color other than the color of the target to identify an intended response mark at the expected location of the target.
4. A system as in claim 3 , wherein the response sheet has key marks and response targets printed in red.