Crop Set of Images to Largest Area in Set

Question

Pardon the title not making any sense.

I have a set of images (the total number of images varies), all square (i.e. usually 200 × 200 or 1000 × 1000)

They're sprites for a game, and I need to crop all images to the smallest possible area that still includes all pixels but for all images.

Let's say this image was originally 200 × 200, but when cropped down to only visible pixels, it's 140 × 100,

Let's say this image was originally 200 × 200, but when cropped down to only visible pixels, it's 100 × 140.

I want to crop both these images to 140 × 140, because that's the size that would not crop out any pixels in any image in the set.

I have hundreds of sets of images so manually calculating it like the aforementioned isn't an option. Any suggestions?

Answer 1

In Photoshop there is a pretty straightforward way to do this.

Unfortunately this method adds a lot of noise to the filenames, but perhaps you can find a way to fix that afterwards.

First we'll gather the original images as layers in one document with the same document size as the largest of the images:

• Select File > Scripts > Load Files into Stack.
• Set Source Files > Use to Folder.
• Click the Browse button and locate the folder with the original files.
• Leave the two checkboxes unticked.
• Click OK.

Now we'll export all the layers trimmed to their smallest possible area:

• Select File > Export > Layers to Files.
• Click Browse to locate a folder you want to export to.
• Tick Trim Layers.
• Setup according to your needs.
• Click Run to save the files.
• Close the document. No need to save it.

Then we'll gather the trimmed images as layers in one document with the same document size as the largest of the images:

• Select File > Scripts > Load Files into Stack.
• Set Source Files > Use to Folder.
• Click the Browse button and locate the folder with the trimmed files.
• Leave the two checkboxes unticked.
• Click OK.

The images will be placed in top left corner of the document. If you want them to be centered you can do this:

• Select all layers in the Layers panel.
• Select the Move Tool.
• Click the Align horizontal centers in the top of the screen.
• Click the Align vertical centers in the top of the screen.

Finally we will export all the layers without trimming them:

• Select File > Export > Layers to Files.
• Click Browse to locate a folder you want to export to.
• Untick Trim Layers.
• Setup according to your needs.
• Click Run to save the files.
• Close the document. No need to save it.

Answer 2

With Gimp:

1. Open a first image
2. Use File > Open as layers to load the rest of the images in the set. You can select several images at once so you can load the whole set in one go.
3. Image > Crop to content crops the image to the smallest rectangle that contains all the non-transparent parts
4. Use a script to re-export all layers to individual files, like for instance ofn-export-layers.

Answer 3

Might be possible to do something with Photoshop CC: Use the new Select Subject functionality. Expand the selection by 1px. Then do Image > Crop. You could record all this as an Action. Then apply the Action to a whole batch of PNGs using File > Automate > Batch.

The beauty of this is that it doesn't matter where the image is positioned in the original 200 x 200 image, as long as it's not too close to an edge. Also, no need to write any code.