Line segment detector

A line segment detector comprising:

• a plurality of first weighted average means, respectively provided for color components, for calculating weighted averages of pixel values in first detection windows set in a first neighboring area of a target pixel in a color input image;
• a plurality of second weighted average means, respectively provided for color components, for calculating weighted averages of pixel values in second detection windows set in a second neighboring area point symmetrical with the first neighboring area with respect to the target pixel;
• a plurality of differentiating means, respectively provided for the color components, for calculating absolute values of differences between outputs from said first and second weighted average means;
• a plurality of dot detecting means, respectively provided for the color components, for calculating averages of absolute values of differential values between pixels in a direction of at least one of a vertical line, horizontal line, left-to-right downward slanting line, and left-to-right upward slanting line within third detection windows set in an area containing the target pixel;
• a plurality of differential amount calculating means, respectively provided for the color components, for subtracting outputs from said dot detecting means from outputs from said differentiating means;
• differential amount/distance calculating means for calculating a distance between the first and second detection windows in a color space on the basis of outputs from said differential amount calculating means;
• and
• comparing means for, if an output from said differential amount/distance calculating means is larger than a predetermined threshold, determining that a portion near the target pixel is one of a vertical line image, horizontal line image, left-to-right downward slanting line image, and left-to-right upward slanting line image.