9-slice scaling with imagemagick? - image-processing

Question

Given an input image of dimensions 120x120 pixels,
I'd like to use imagemagick to perform
9-slice scaling.
keep the image within the box bounded by
top-left coordinate (10,10)
and bottom right coordinate (110,110) unscaled,
This centre section is 100x100 pixels.
The left side scale by a given factor,
say 3, so this would go from 10x100 pixels to 30x100 pixels
The right side scale by a given factor,
say 2, so this would go from 10x100 pixels to 20x100 pixels
The top and bottom side both scale by a given factor,
say 1.5, so these would go from 100x10 to 100x15 each.
The four corners would scale to fit the new dimensions of the new top, right, bottom, and left sides.
Something similar to
(except in my case the centre element, "5", doesn't need to change)
How can I perform this operation using imagemagick?
(Suggestions for any other CLI tool available on Linux also welcome!)

Answer 1

Using ImageMagick you can approach this as a series of isolated cropping and resizing operations. Here's an example command...
magick input.png -write mpr:img0 +delete ^
( mpr:img0 -gravity west -crop 10x+0+0 -resize 300x100% ) ^
( mpr:img0 -shave 10x0 ) ^
( mpr:img0 -gravity east -crop 10x+0+0 -resize 200x100% ) ^
+append +repage -write mpr:img0 +delete ^
( mpr:img0 -gravity north -crop x10+0+0 -resize 100x150% ) ^
( mpr:img0 -shave 0x10 ) ^
( mpr:img0 -gravity south -crop x10+0+0 -resize 100x150% ) ^
-append +repage result.png
This command will take a 10 pixel wide strip from the left and right sides, widen the left by 300% and the right by 200%, and re-append them to the center.
Then it follows by taking a 10 pixel high strip from the top and bottom, resizing both their heights to 150%, and re-appending them to the center section.
The corners get properly scaled because they go through both the horizontal and vertical resizing operations.
The command uses IMv7 in Windows CLI syntax. For a Windows BAT script you need to double the percent signs "%%".
To make it work on a *nix system change the continued-line carets "^" to backslashes "\" and escape the parentheses with backslashes "\(...\)".
To use it with IMv6 change "magick" to "convert".

Answer 2

Here is one way to do that in ImageMagick 6 (Unix syntax).
Input:
convert logo.png -write mpr:img +delete \
\( \
\( mpr:img -gravity northwest -crop 10x10+0+0 +repage -resize 300x150%! \) \
\( mpr:img -gravity north -crop 100x10+0+0 +repage -resize 100x150%! \) \
\( mpr:img -gravity northeast -crop 10x10+0+0 +repage -resize 200x150%! \) \
+append \
\) \
\( \
\( mpr:img -gravity west -crop 10x100+0+0 +repage -resize 300x100%! \) \
\( mpr:img -gravity center -crop 100x100+0+0 +repage \) \
\( mpr:img -gravity east -crop 10x100+0+0 +repage -resize 200x100%! \) \
+append \
\) \
\( \
\( mpr:img -gravity southwest -crop 10x10+0+0 +repage -resize 300x150%! \) \
\( mpr:img -gravity south -crop 100x10+0+0 +repage -resize 100x150%! \) \
\( mpr:img -gravity southeast -crop 10x10+0+0 +repage -resize 200x150%! \) \
+append \
\) \
-append \
logo_result.png
Result:
If using ImageMagick 7, then change convert to magick.
If on Windows, change the line endings \ to ^ and remove the \ from the ( and ). If in .bat file, double the % to %%.