warp

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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 q and r will be printed if the -qr flag is set.

If -rss is 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 cpfile consists of pairs of points. Each line is a set of i, j, k and l. i and j are coordinates in the reference image. k and l are 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 separated by 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 inimage and outimage are specified, the transform will be performed. The interpolation method -ip is

 -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 startpoint than the input image, this may be specified by the -xstart, -xstop, -xsize, -ystart, -ystop and -ysize options. If start, stop as well as size options are given, and inconsistently, the stop option is ignored. The given sizes are clipped against the result of the transform.

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

warp

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