How to scale and crop a folder of images? - image-processing

Question

I've been looking at the documentation for imagemagick and looking at examples of scripts others have made, but I haven't been able to get this working.
The goal is to have imagemagick scale, crop, and save (appending the dimensions to the file names) multiple resized images of various aspect ratios.
For example, a folder containing Image1.png and Image2.png would result in:
Image1_1571x2646.png, Image1_1350x2150.png, Image1_1281x2039.png
Image2_1571x2646.png, Image2_1350x2150.png, Image2_1281x2039.png
Visual aid:
The animation above shows the simplest examples: a 1:1 square, a vertical rectangle, and a horizontal rectangle.
The images should scale to fit the longest dimension of the rectangle, and then crop any leftover pixels. The scaling and cropping should be done relative to the image centers.
Here's what I have so far (using macOS Terminal) but it doesn't work:
convert *.png -path /Users/user/Resized \
\( +clone -resize "1571x2646^” -gravity center -crop 1571x2646+0+0 +repage resultimage -write 1571x2646.png +delete \) \
\( +clone -resize "1350x2150^” -gravity center -crop 1350x2150+0+0 +repage resultimage -write 1350x2150.png +delete \) \
-resize "1281x2039^” -gravity center -crop 1281x2039+0+0 +repage resultimage 1281x2039.png
I'm not sure if I should use mogrify or convert, but if I use mogrify clone gives an error. I'm also not sure if multi-line instructions need to be put into a .sh file or something. The ^ denotes the dimension that should take priority (the larger one). I believe -gravity center is supposed to keep scaling and cropping relative to the image centers.

Answer 1

With Imagemagick, you must use convert. Mogrify cannot handle the parenthesis process and clones, nor can it write multiple outputs for a given input. The ^ is the correct way and -gravity center is correct. You will have to loop over each input image. I do not think you can use wild cards to process more than one image at a time with this type of command. I think -path is only for mogrify.
I would write a loop over each of your input images (bash unix syntax):
cd
cd /Users/user/Resized/
list=`ls`
for img in $list; do
name=`convert "$img" -format "%t" info:`
convert "$img" \
\( -clone 0 -resize "1571x2646^" -gravity center -crop 1571x2646+0+0 +repage +write ${name}_1571x2646.png +delete \) \
\( -clone 0 -resize "1350x2150^" -gravity center -crop 1350x2150+0+0 +repage +write ${name}_1350x2150.png +delete \) \
\( -clone 0 -resize "1281x2039^" -gravity center -crop 1281x2039+0+0 +repage +write ${name}_1281x2039.png +delete \) \
null:
done
The above assumes that your input images have no spaces in their names.
I have changed from +clone to -clone 0, since I am not sure if you change aspect ratio from output to output whether that will cause problems. You can try both ways and see which looks best.