Image line-segment extracting apparatus

• US 5,629,989 A
• Filed: 04/18/1994
• Issued: 05/13/1997
• Est. Priority Date: 04/27/1993
• Status: Expired due to Term

• Current Assignee: Honda Giken Kogyo Kabushiki Kaisha (Honda Motor Company)
• Original Assignee: Honda Giken Kogyo Kabushiki Kaisha (Honda Motor Company)
• Inventors: Osada, Taku
• Primary Examiner(s): Boudreau, Leo
• Assistant Examiner(s): Tadayon, Bijan
• Application Number:
  US08/229,371
• Time in Patent Office: 1,121 Days
• Field of Search: 382/193, 382/199, 382/202, 382/281, 382/192, 382/194, 382/168, 382/169, 382/170, 382/171, 382/172, 382/190, 382/191, 382/195, 382/201, 382/203, 382/204, 382/205, 382/224 , 382/266, 382/268, 382/269, 382/286, 382/141, 382/151, 364/413.13, 364/413.23, 364/725, 364/478.01
• US Class Current: 382/281
• CPC Class Codes: G06V 10/48 by mapping characteristic values of the pattern into a parameter space, e.g. Hough transformation

Abstract

An image line-segment extracting apparatus which in processing steps to conduct Hough transformation of a sequence of edge pixels composing an image, to plot a histogram based on Hough function values, to successively detect peaks from the histogram and to extract a plurality of line segments existing in the image, can detect the only true peaks, effectively eliminating false peaks. The process also includes a feature by which region is defined and the amount of influence of a remarkable one of the peaks in a histogram upon frequency distribution on the histogram are determined and then histogram frequency values of other peaks in the defined region are corrected according to the determined amount of influence to partially rewrite the histogram.

Claims

1. An image line-segment extracting apparatus which extracts a sequence of pixels (dots) of an edge in an image from a digital image composed of pixels, conducts Hough transformation of the sequence of pixels, plots a histogram according to the Hough transform function values, detects a peak of frequency on the histogram, and extracts a line segment corresponding to the detected peak from the image, characterized in that:

the apparatus includes means to determine a scope in which influence may appear and an amount of influence that may prevent the extraction of a line segment of a specified peak to be an object of line segment extracting processing detected on the histogram upon frequency distribution thereof;

means to determine whether another peak besides the specified peak exists in the region of influence;

means to correct a histogram frequency value of each of detected peaks other than the specified peak and their neighboring points in the histogram defined to be in the region of influence according to the determined amount of influence; and

means for detecting a peak in the corrected histogram and then extracting a line segment corresponding to said peak in the corrected histogram detected by said detecting means.

2. An image line-segment extracting apparatus which extracts a sequence of pixels of an edge in an image from a digital image composed of pixels, conducts Hough transformation of the sequence of pixels, plots a histogram according to the Hough transform function values, detects a peak of frequency on the histogram, and extracts a line segment corresponding to the detected peak from the image, characterized in that;

the apparatus includes means to determine a scope in which influence may appear and an amount of influence that may prevent extraction of a line segment of a specified peak to be an object of line segment extracting processing detected on the histogram upon frequency distribution thereof;

means to determine whether another peak besides the specified peak exists in the region of influence;

means to correct a histogram frequency value of each of the detected peaks other than the specified peak and their neighboring points in the histogram, defined to be in the region of influence according to the determined amount of influence;

means for determining Hough function curves of both ends Qs (Xs, Ys) and Qe (Xe, Ye) of a straight line located in a two-dimensional (X-Y) coordinate system, said straight line corresponding to a specified peak Po (ρ

o, θ

o);

where ρ and

θ

are Hough coordinate axes, (Ys, Ys) indicates a position of a point Qs at one end of a line in the (X-Y) coordinate system and (Xe, Ye) indicates a position of a point Qe at the other end of the line in the (X-Y) coordinate system;

means for calculating an amount of influence of the specified peak Po upon any peak P (ρ

, θ

o+dθ

) in a region K in a Hough coordinate system according to expressions;

space="preserve" listing-type="equation">P(ρ

, θ

o+dθ

)=Po(ρ

o, θ

o)/l{∀

p|(ρ

, θ

o+dθ

)ε

K}. (1) ##EQU3## where l is an interval of direction of ρ

-axis in each Hough function curve at a position apart from a point θ

o by a distance dθ

in the Hough coordinate system and wherein K is a line segment that is parallel to a ρ

-axis in each Hough function curve at a position (Po+dθ

) apart from θ

o by dθ

; and

means for detecting a peak in the corrected histogram and then extracting a line segment corresponding to said peak in the corrected histogram detected by said detecting means.

3. An image line-segment extracting apparatus as defined in claim 2, characterized in that the apparatus is capable of detecting a sequence of searched edge points as a line segment.