I have an image 500 by 20 000 pixels. I need to slice it to smaller ones that are 1000 pixels height and 100% width (I don't want to hard-code width).
For this, I use this one-line script:
input=input.png; width=$(magick identify -format %w $input); magick $input -crop ${width}x1000 +repage output%d.png
But maybe there is a shorter solution? I tried to combine 100% with 1000 pixels, but this doesn't seem to work:
magick input.png -crop 100%x1000 +repage output%d.png
There are several ways to use ImageMagick to crop an image into pieces of a given height and maintain the width of the input image. A very simple method might be...
magick input.png -crop 0x1000 +repage output%d.png
Using "0" for the crop width will maintain the input width.
Another similar method uses the variable %[w] for "width"...
magick input.png -crop %[w]x1000 +repage output%d.png
Addendum by Mark Setchell
You can omit the zero for the width altogether and it will equally retain the width. You can also use %03d to zero-pad the numbers in the extracted image filenames out to 3 digits, then they will sort in order:
magick input.png -crop x1000 +repage parts-%03d.png
Results in:
-rw-r--r-- 1 mark wheel 369 23 Aug 10:13 parts-000.png
-rw-r--r-- 1 mark wheel 369 23 Aug 10:13 parts-001.png
-rw-r--r-- 1 mark wheel 369 23 Aug 10:13 parts-002.png
...
...
-rw-r--r-- 1 mark wheel 368 23 Aug 10:13 parts-197.png
-rw-r--r-- 1 mark wheel 367 23 Aug 10:13 parts-198.png
-rw-r--r-- 1 mark wheel 376 23 Aug 10:13 parts-199.png