autoshrink with aspect ratio

Question

Is there any simple way to autocrop/autoshrink a square image in GIMP, but without changing aspect ratio? Basically the autoshrinking would stop once it's no longer possible to maintain height and width equality.

I've been using this with imagemagick and powershell:

convert $files[$i].Name -set option:size '%[fx:max(w,h)]x%[fx:max(w,h)]' 
\ xc:none +swap -gravity center -composite $outfile

Preferably would like to do this with scheme/script-fu.

Answer 1

• Duplicate layer
• Autocrop copy
• Figure out the size and offsets of a potential square crop of the layer from the cropped width, height and offsets.
• remove copy
• crop the original layer using gimp-layer-resize

Something like this:

# -*- coding: utf-8 -*-
#!/usr/bin/env python

import os, sys
from gimpfu import *

def squareCrop(image,layer):
    pdb.gimp_image_undo_group_start(image)

    try:
        x0,y0=layer.offsets

        # get size and offsets of fully autocropped layer
        copy=layer.copy()
        image.add_layer(copy)
        pdb.plug_in_autocrop_layer(image,layer)
        xC,yC=copy.offsets
        hC,wC=copy.height,copy.width
        image.remove_layer(copy)

        # determine padding direction
        topBottomPad=wC > hC
        pad=abs(hC-wC)/2

        # determine size and offsets for resize
        xOff,yOff=(x0-xC,y0+pad-yC) if topBottomPad else (x0+pad-xC,y0-yC)
        w,h=(wC,wC) if topBottomPad else (hC,hC)

        layer.resize(w,h,xOff,yOff)

    except Exception as e:
        print e.args[0]
        pdb.gimp_message(e.args[0])

    pdb.gimp_image_undo_group_end(image)

### Registrations
whoiam='\n'+os.path.abspath(sys.argv[0])

register(
    'square-crop',
    'Square crop'+whoiam,
    'Square crop',
    'Ofnuts','Ofnuts','2016',
    'Square crop...',
    "RGB*",
    [
        (PF_IMAGE, "image", "Input image", None),
        (PF_DRAWABLE, "drawable", "Input drawable", None),
    ],
    [],
    squareCrop,
    menu="<Image>/Layer/Transform",
)

main()

Note you cannot crop that way if you are too close to a border, because the padding would extend beyond the canvas limits (something which isn't checked by the code above)

Answer 2

Here's my solution:

(define (square image drawable)
    (gimp-image-undo-group-start image)
    (gimp-context-push)
    (plug-in-autocrop 1 image drawable)
    (let* (
        (width (car (gimp-image-width image)))
        (height (car (gimp-image-height image)))
        (newWidth width)
        (newHeight height)
        (layer (vector-ref (cadr (gimp-image-get-layers image)) 0))
    )

        (if (< width height)
            (set! newWidth height)
        )
        (if (> width height)
            (set! newHeight width)
        )

        (gimp-image-resize image newWidth newHeight (/ (- newWidth width) 2) (/ (- newHeight height) 2))
        (gimp-layer-resize-to-image-size layer)

        (gimp-image-clean-all image)
        (gimp-context-pop)
        (gimp-image-undo-group-end image)
        (gimp-displays-flush)

        (list newWidth newHeight)
    )
)
(script-fu-register
    "square"
    "<Image>/Tools/Square"
    ""
    "Matthew Morrone"
    "Uncopyright 2016 Matthew Morrone"
    "27 September 2016"
    "*"
    SF-IMAGE "Input Image" 0
    SF-DRAWABLE "Input Drawable" 0
)