teem	/	bin	ilk

This page gives a summary of the various capabilities of ilk. Everytime that an image is preceeded by some text in mono-spaced font, that text can be pasted into a shell in order to regenerate the image. This assumes that ilk, unu, and cjpeg are all in your path, or are aliased.

General Usage Information

ilk: (I)mage (L)inear Trans(X-->K)forms. Applies linear (homogenous
coordinate) transforms to a given image, using the given kernel for resampling.

Usage: ilk [@file ...] [-i <image>] [-0 <origin>] -t <xform0 ...> \
       [-k <kernel>] [-min <xMin yMin>] [-max <xMax yMax>] [-b <boundary>] \
       [-bg <bg0 bg1 ...>] [-s <xSize ySize>] [-o <filename>]

        @file ... = response file(s) containing command-line arguments
       -i <image> = input image; default: "-"
      -0 <origin> = where to location (0,0) prior to applying transforms.
                  o "u:<float>,<float>" locate origin in a unit box
                    [0,1]x[0,1] which covers the original image
                  o "p:<float>,<float>" locate origin at a particular
                    pixel location, in the index space of the image
                    default: "p:0,0"
  -t <xform0 ...> = transform(s) to apply to image. Transforms are applied in
                    the order in which they appear.
                  o "identity": no geometric transform, just resampling
                  o "translate:x,y": shift image by vector (x,y), as
                    measured in pixels
                  o "rotate:ang": rotate CCW by ang degrees
                  o "scale:xs,ys": scale by xs in X, and ys in Y
                  o "shear:fix,amnt": shear by amnt, keeping fixed the
                    pixels along a direction <ang> degrees from the X axis
                  o "flip:ang": flip along axis an angle <ang> degrees
                    from the X axis
                  o "a,b,c,d,tx,ty": specify the transform explicitly 
                    (1 or more 2D transforms)
      -k <kernel> = reconstruction kernel; default: "cubic:0,0.5"
 -min <xMin yMin> = lower bounding corner of output image. Default (by not
                    using this option) is the lower corner of input image.
                    (2 doubles)
 -max <xMax yMax> = upper bounding corner of output image. Default (by not
                    using this option) is the upper corner of input image.
                    (2 doubles)
    -b <boundary> = what to do when sampling outside original image.
                  o "bleed": copy values at image border outward
                  o "wrap": do wrap-around on image locations
                  o "pad": use a given background value (via "-bg")
                    default: "bleed"
-bg <bg0 bg1 ...> = background color to use with boundary behavior "pad".
                    Defaults to all zeroes. (1 or more floats)
 -s <xSize ySize> = For each axis, information about how many samples in
                    output:
                  o "x<float>": number of output samples is some scaling
                    of the number input samples; multiplied by <float>
                  o "<int>": specify exact number of samples
                    (2 sampling specifications)
                    default: "x1 x1"
    -o <filename> = file to write output nrrd to (string); default: "-"

Options which will be used verbatim many times may be entered into a "response file"; when these are indicated on the command line with "@filename", the contents of the file are effectively inserted there on the command line. Within the response file, line breaks count as white space, and comments lines begin with "#".

Demonstration image

unu resample -i huysumcrop.ppm -s = x0.6 x0.6 -o init.ppm
cjpeg -quality 99 init.ppm > init.jpg

The output of ilk is a NRRD file, but it will have the same dimension and type as the input 8-bit color image, which means it can be converted to a PPM file (really just changing the header), and then saved as a JPEG, with the following sequence:

 ... | unu save -f pnm | cjpeg -quality 99 out.jpg

alias tojpg "unu save -f pnm | cjpeg -quality 99"

The axes, the origin

(0,0) -----------> X
  |
  |
  |
  v

  Y

There are two ways of specifying the origin to ilk:

1. -0 u:<X>,<Y>: The (X,Y) location of the origin is relative to position inside a unit box spanning the image, using the same axes orientation as shown above. -0 u:0.5,0.5 is the center of the image.
2. -0 p:<X>,<Y>: The (X,Y) location of the origin is in the index space of the image itself, so these are effectively pixel locations (but they don't have to be integers).

• Scaling: scale by (possibly different) amounts in X and Y, based on where the origin is set
• Flipping: Can flip across a line at an arbitrary orientation
• Rotations with scalings: Demonstrates the different boundary behaviors that can be specified.
• Translations, Shear: These too are possible!
• Arbitrary transforms: You can specify the individual elements of the transform matrix
• Composition of transforms: You can specify an arbitrary number of transforms on the command line, and ilk will multiply them together prior to resampling.
• Kernel choice: Information about the different kernels availble in ilk
• Kernel quality evaluated with multiple resamplings: How multiple passes through ilk can serve as an indicator of reconstruction kernel quality.
• Explicitly setting min, max, sizes: How to resample on a different domain than the original image, or at a different resolution.