How to split up large photos

Doodler works well with small to medium sized imagery where the features and objects can be labeled without much or any zoom or pan. This depends a lot on the image resolution and content so it is difficult to make general guidelines.

But it's easy enough to chop images into pieces, so you should experiment with a few different image sizes.

Let's start with this image called big.jpg:

I recommend the command-line program imagemagick, available for all major platforms. It's an incredibly powerful and useful set of tools for manipulating images. You can use the imagemagick command line tools for splitting and merging imagery. We use the magick command (convert on some Linux distributions)

Halves

Split into two lengthways:

magick big.jpg -crop 50%x100% +repage fordoodler_%02d.jpg

Quarters

Following the same logic, to chop the image into quarters, use:

magick big.jpg -crop 50%x50% +repage quarters_fordoodler_%02d.jpg

The first two quarters are shown below:

Specific size

To chop the image into tiles of a specific size, for example 1024x1024 pixels, use:

magick big.jpg -crop 1024x1024 +repage px1024_fordoodler_%02d.jpg

The first three tiles are shown below:

Easy peasy!

Recombine

After you've labeled, you may want to recombine your label image. Imagemagick includes the montage tool that is handy for the task. For example, the image quarters can be recombined like this:

magick montage -mode concatenate -tile 2x2 quarters*.jpg recombined.jpg

and the equivalent command to combine the two vertical halves is:

magick montage -mode concatenate -tile 2x1 fordoodler*.jpg recombined.jpg

Happy image cropping!