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WARP

Section: User Commands (1)
Updated: 16 Mar 1998
Index

NAME

warp - polynomial control point mapping

SYNTAX

warp [-ip <n>] [-bg <bg>] [-cp <cpfile>] [-p <poldeg>]
      [-xstart <xstart>] [-xstop <xstop>]
      [-xsize <xsize>] [-ystart <ystart>]
      [-ystop <ystop>] [-ysize <xsize>]
      [-rss] [-qr] [ <inimage> <outimage> ]

DESCRIPTION

Perform an output to input mapping (k,l) = M(i,j).Given an input image I(k, l), calculate O(i,j).
If 'poldeg' == 1 (default) :
k = Q(i, j) = q0 + i * q1 + j * q2
l = R(i, j) = r0 + i * r1 + j * r2
If 'poldeg' == 2 :
k = Q(i, j) = q0 + i*q1 + j*q2 + i*i*q3 + i*j*q4 + j*j*q5
l = R(i, j) = r0 + i*r1 + j*r2 + i*i*r3 + i*j*r4 + j*j*r5

The coefficients qand rwill be printed if the -qrflagis set.

If -rssis set, the residuals r(m) will be calculated:
dk = k - Q(i,j)
dl = l - R(i,j)
r(m) = sqrt(dk*dk + dl*dl)

The control point file cpfileconsists of pairs of points.Each line is a set of i,j,kand l.iand jare coordinates in the reference image.kand lare coordinates in the image to be transformed.Lines with # in coloumn 1 are treated as comment lines.Blank lines are ignored. Pixels inside a line are separatedby blanks, lines are separated by newline.
#
# Example 1
#
#   i   j    k   l
#------------------
    57  44   61 144
    27  72   38 180
   114 122  132 201
   180 199  213 255
   193 166  215 217
   191 288  241 336

If inimageand outimageare specified, the transformwill be performed.The interpolation method -ipis
-ip 0 : Nearest neighbor
-ip 1 : Bilinear   interpolation
         g(x) = bi(f(x), f(x+1), d)
         bi(x, y, d) = x(1-d) + yd
-ip 3 ; Cubic      interpolation
         g(x) = cc(f(x-1), f(x), f(x+1), f(x+2), d)
         cc(x, y, z, v, d) = y + d((-x+z) +
                             d((2x-2y+z-v) + d(-x+y-z+v)))

Default is bilinear interpolation (-ip 1).

If the output image should have another size or startpointthan the input image, this may be specified by the-xstart,-xstop,-xsize,-ystart,-ystopand -ysizeoptions. If start, stop as well as size options are given, andinconsistently, the stop option is ignored. The givensizes are clipped against the result of the transform.

-bgis used to specify the background pixel value,default = 0.

REFERENCE

Wayne Niblack. Digital Image Processing, p 131-150

RESTRICTIONS

Works on unsigned byte images only.

AUTHOR

Lennart Flem 1/3-91.

MODIFIED

Otto Milvang

EXAMPLES

ID

$Id: warp.c,v 1.28 1997/04/23 13:00:00 svein Exp $

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