Fred's ImageMagick Scripts



    Licensing:

    Copyright © Fred Weinhaus

    My scripts are available free of charge for non-commercial (non-profit) use, ONLY.

    For use of my scripts in commercial (for-profit) environments or non-free applications, please contact me (Fred Weinhaus) for licensing arrangements. My email address is fmw at alink dot net.

    If you: 1) redistribute, 2) incorporate any of these scripts into other free applications or 3) reprogram them in another scripting language, then you must contact me for permission, especially if the result might be used in a commercial or for-profit environment.

    Usage, whether stated or not in the script, is restricted to the above licensing arrangements. It is also subject, in a subordinate manner, to the ImageMagick license, which can be found at: http://www.imagemagick.org/script/license.php

    Please read the Pointers For Use on my home page to properly install and customize my scripts.

WARPLOG


Resizes an image according to a logarithmic transformation.

Download Script

last modified: February 28, 2021



USAGE: warplog [-w width] [-h height] [-b bgcolor] infile outfile
USAGE: warplog [-help]

-w width ...... desired output width; value in pixels; logarithmic
............... stretch/compression applied only if width is specified
-h height ..... desired output height; value in pixels; logarithmic
............... stretch/compression applied only if height is specified
-b bgcolor .....background color for virtual pixels; default is black

PURPOSE: To resize an image (stretch or compress) according to a logarithmic transformation.

DESCRIPTION: WARPLOG resizes an image (stretch or compress) according to a logarithmic transformation. The log transform will be applied to the width and/or height, if specified.

ARGUMENTS:

-w width ... WIDTH is the desired output width. Value in pixels. The logarithmic stretch/compression is applied only if width is specified.

-h height ... HEIGHT is the desired output height. Value in pixels. The logarithmic stretch/compression applied only if height is specified

-b bgcolor ... BGCOLOR is the background color for virtual pixels. Any IM valid color may be specified. Typically, there should be no need for the virtual pixel color to be specified. The default is black.

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.


EXAMPLES


Example 1

Original

Arguments:
-w 402
(2x horizontal stretch)

Arguments:
-h 402
(2x vertical stretch)

Arguments:
-w 402 -h 402
(2x horizontal and vertical stretches)

Arguments:
-w 201 -h 201
(1x horizontal and vertical distortion)



Example 2

Original

Arguments:
-w 512
(2x horizontal stretch)

Arguments:
-h 512
(2x vertical stretch)

Arguments:
-w 512 -h 512
(2x horizontal and vertical stretches)

Arguments:
-w 256 -h 256
(1x horizontal and vertical distortion)



What the script does is as follows:

  • Reads the input image
  • Applies an -fx computation to achieve a natural
    stretch or distortion
  • Saves the output

This is equivalent to the following IM commands for a horizontal stretch

  • declare `convert -ping "$infile" -format "ww=%w\nhh=%h\n" info:`
  • convert -size ${dwidth}x${hh} xc: "$infile" \
    -background "$bgcolor" -virtual-pixel background \
    -fx "v.p{exp(ln(v.w)*i/(w-1))-1,j}" "$outfile"