TIEVisionImage.houghLinesP

Declaration

function houghLinesP(rho: double; theta: double; threshold: int32_t; minLineLength: double = 0; maxLineGap: double = 0): TIEVisionVectorScalarInt32; safecall;

Description

Find line segments in a binary image using the probabilistic Hough transform.
Returns a vector (list) of line segments. Each line is represented by a 4-element vector (x1, y1, x2, y2), where (x1, y1) and (x2, y2) are the ending points of each detected line segment.

Note:
◼ Pixel format of input image must be ie8g.
◼ You can draw the lines to a canvas using DrawLines

Parameter	Description
rho	Distance resolution of the accumulator in pixels
theta	Angle resolution of the accumulator in radians
threshold	Accumulator threshold parameter. Only those lines are returned that get enough votes
minLineLength	Minimum line length. Line segments shorter than that are rejected
maxLineGap	Maximum allowed gap between points on the same line to link them

Comparison of Line Detection Methods

// HOUGH TRANSFORM
ImageEnView1.IEBitmap.PixelFormat := ie8g;
ImageEnView1.IEBitmap.GetIEVisionImage().blur( IEVisionSize(3, 3), IEVisionPoint(-1, -1) );
ImageEnView1.IEBitmap.GetIEVisionImage().canny( 50, 200, 3 );
lines := ImageEnView1.IEBitmap.GetIEVisionImage().houghLinesP( 1, PI / 180, 200, 100, 10 );
for i := 0 to lines.size() - 1 do
begin
  sc := lines.getScalarInt32(i);

  with ImageEnView1.IEBitmap.Canvas do
  begin
    Pen.Width := 2;
    Pen.Color := clRed;
    MoveTo( sc.val[0], sc.val[1] );
    LineTo( sc.val[2], sc.val[3] );
  end;
end;
ImageEnView1.Proc.TextOut( Align_Text_Near_Left, Align_Text_Near_Top, Format( 'Lines: %d', [ lines.size ]), 'Arial', 12, Text_Color, [fsBold] );
ImageEnView1.Update();

// BINARY DESCRIPTOR
lines := ImageEnView1.IEBitmap.GetIEVisionImage().detectLines( ievBinaryDescriptor );
for i := 0 to lines.size() - 1 do
begin
  sc := lines.getScalarInt32(i);

  with ImageEnView1.IEBitmap.Canvas do
  begin
    Pen.Width := 2;
    Pen.Color := clRed;
    MoveTo( sc.val[0], sc.val[1] );
    LineTo( sc.val[2], sc.val[3] );
  end;
end;
ImageEnView1.Proc.TextOut( Align_Text_Near_Left, Align_Text_Near_Top, Format( 'Lines: %d', [ lines.size ]), 'Arial', 12, Text_Color, [fsBold] );
ImageEnView1.Update();

// LSD DETECTOR
lines := ImageEnView1.IEBitmap.GetIEVisionImage().detectLines( ievLSDDetector );
for i := 0 to lines.size() - 1 do
begin
  sc := lines.getScalarInt32(i);

  with ImageEnView1.IEBitmap.Canvas do
  begin
    Pen.Width := 2;
    Pen.Color := clRed;
    MoveTo( sc.val[0], sc.val[1] );
    LineTo( sc.val[2], sc.val[3] );
  end;
end;
ImageEnView1.Proc.TextOut( Align_Text_Near_Left, Align_Text_Near_Top, Format( 'Lines: %d', [ lines.size ]), 'Arial', 12, Text_Color, [fsBold] );
ImageEnView1.Update();

TIEVisionImage.houghLinesP