USAGE: quadcorners2 [-L lower] [-U upper] [-a area] [-o openM] [-c closeM] [-b blursize] [-f filtersize] [-s skip] [-i images] [-k kind] [-C color] [-r radius] [-t textoffset] infile
USAGE: quadcorners2 [-help]

-p ... pad .......... border pad amount for input image to help in getting
..................... good Hough lines; integer>=0; default=0 (no padding)
-L ... lower ........ lower color threshold for extracting quadrilateral; comma
..................... separated triplet in the form of either 8-bit grayscale or
..................... percent color values (for srgb color); if only 1 value provided,
..................... it will be duplicated three times; default=50% (mid gray)
-U ... upper ........ upper color threshold for extracting quadrilateral; comma
..................... separated triplet in the form of either 8-bit grayscale or
..................... percent color values (for srgb color); if only 1 value provided,
..................... it will be duplicated three times; default=100% (white)
-a ... area ......... area threshold in pixels for removing small regions from the
..................... thresholded image; integer>=0; default=0 (skip connected
..................... components filtering)
-o ... openM ........ morphology open diamond size for preprocessing to remove all
..................... white regions outside the main quadrilateral in the threshold
..................... image; integer>0; default is no morphology open
-c ... closeM ....... morphology close disk size for preprocessing to remove all
..................... black regions inside the main white quadrilateral in the
..................... threshold image; integer>0; default is no morphology close
-b ... blursize ..... size of 1D blur (smoothing) filter (pixels); integer>0; default=5
-f ... filtersize ... size of 1D derivative filter (pixels); integer>0; default=5
-s ... skip ......... skip (in pixels) as the minimum distance between peaks
..................... in the polar image; integer>0; default=50 (must be larger
..................... than the filtersize)
-i ... images ....... keep ancillary processing images (especially for debugging);
..................... choices are: view (v) or save (s); default is neither
-k ... kind ......... kind of ancillary processing images; choices are: threshold (t),
..................... cleaned (c), (convex) hull (h), (Hough) lines (l),
..................... final (corners) (f) or all (a)
-C ... color ........ color used when drawing on various images; any IM color value
..................... is allowed; default=red
-r ... radius ....... radius for circle used to mark corners; integer>0; default=2
-t ... textoffset ... text offset of TL, TR, BR, BL annotation relative to corner;
..................... +X+Y format, integers for X and Y; default="+0-15"

PURPOSE: To optionally threshold an image if not already binary and find the four corners of the binary quadrilateral from the maximum curvature of the outline obtained from the convex hull.

DESCRIPTION: QUADCORNERS2 optionally thresholds an image, if not already binary, and finds the four corners of a quadrilateral in the binary image. The process is 1) optionally color threshold the image; 2) optionally apply morphology to clean and smooth the outline of the image; 3) optionally apply connected components processing to remove small regions; 4) get a white filled convex hull on black background image 5) convert the convex hull image to polar coordinates and scale to 1 row; 6) extract the reverse polar coefficients; 7) convert the 1D polar image heights to 1D x and y images using the reverse coefficents; 8) apply 1D first and second order derivative to the 1D x and y images; 9) use the x and y derivatives to compute a 1D curvature image; 10) find the x locations in the 1D curvature image where the curvature is maximum skipping enough between peaks; 11) look up the x and y coordinates associated with peaks locations; 12) sort the top 4 peak x,y coordinates in TL, TR, BR, BL order (i.e., clockwise from TL)

The input image should be a binary quadrilateral. If not, then use the color-threshold, morphology and area to threshold into a clean binary quadrilateral.

Any saved ancillary images will be name for the input_X.png, where X is the kind of ancillary image.

The 4 corner X,Y coordinates of the quadrilateral (in the padded input) will be listed to the terminal in clockwise order starting at the top-left corner

ARGUMENTS:

-p pad ... PAD is the border pad amount for input image to help in getting good Hough lines; integer>=0; default=0 (no padding)

-L lower ... LOWER color threshold for extracting quadrilateral; comma separated triplet in the form of either 8-bit grayscale or percent color values (for srgb color); if only 1 value provided, it will be duplicated three times; default=50% (mid-gray)

-U upper ... UPPER color threshold for extracting quadrilateral; comma separated triplet in the form of either 8-bit grayscale or percent color values (for srgb color); if only 1 value provided, it will be duplicated three times; default=100% (white)

-a area ... AREA threshold in pixels for removing small regions from the thresholded image; integer>=0; default=0 (skip connected components filtering)

-o openM ... OPENM is the morphology open diamond size for preprocessing to remove all white regions outside the main quadrilateral in the threshold image; integer>0; default is no morphology open

-c closeM ... CLOSEM is the morphology close disk size for preprocessing to remove all black regions inside the main white quadrilateral in the threshold image; integer>0; default is no morphology close

-b blursize ... BLURSIZE is the (half) size of the 1D blur smoothing filter (in pixels); integer>0; default=5

-f filtersize ... FILTERSIZE is the (half) size of the 1D derivative filters (in pixels); integer>0; default=5

-s skip ... SKIP (in pixels) is the minimum distance between peaks in the polar image; integer>0; default=50 (must be larger than the filtersize)

-i images ... IMAGES specifies whether to keep ancillary processing images (especially for debugging); choices are: view (v) or save (s); default is neither

-k kind ... KIND of ancillary processing images; choices are: threshold (t), cleaned (c), (convex) hull (h), polar (p), final (corners) (f), or all (a)

-C color ... COLOR used when drawing on various images; any IM color value is allowed; default=red

-r radius ... RADIUS for circle used to mark corner points; integer>0; default=2

-t textoffset ... text offset of TL, TR, BR, BL annotation relative to corner points; +X+Y format, integers for X and Y; default="+0-15"

REQUIREMENTS: Requires IM 7 due to the use of -color-threshold and the convex hull

CAVEAT: No guarantee that this script will work on all platforms, nor that trapping of inconsistent parameters is complete and foolproof. Use At Your Own Risk.