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David G

David G, Chief Explorer

Automate the process of adding a custom branded nadir to all your equirectangular photos using Python and Imagemagick.

Last year I showed you how to use GIMP to manually add a branded nadir to your photos.

In many cases, you will want to add a branded nadir to all of your photos, not just one or two. Using GIMP to do this manually isn’t viable – unless you have A LOT of time on your hands.

For those that have a large amount of images, it’s relatively simple to do this programmatically with the help of Imagemagick.

Imagemagick provides a huge variety of functions to manipulate image files. If you’re a follower of this blog, you might have seen me use it previously to create a cubemap.

This time I’ll show you how to use it to overlay a logo file onto an equirectangular photo to create a branded nadir.

Here is the photo I will use (taken along the South West Coast Path, Cornwall, England earlier this year using the Trek Pack v2), and the Trek View logo I will use for this exercise.

South West Coast Path equirectangular image

Trek View Nadir

If you want to use your own logo, make sure its dimensions are square, and is at least 500px x 500px (ideally larger if your photo has a resolution above 4K).

You can use a logo with a transparent background (in .png format), but in my experience, I find a solid background works best.

Step 1: Convert the logo to an equirectangular projection

I explain why we need to do this in the previous post detailing how to add a branded nadir using GIMP.

Here’s how to do it with Imagemagick:

1.1 Rotate 180 degrees

magick trek-view-square-nadir.png -rotate 180 trek-view-square-nadir-1.png

Rotate 180 degrees

1.2 DePolar Distortion

magick trek-view-square-nadir-1.png -distort DePolar 0 trek-view-square-nadir-2.png

DePolar Distortion

See Imagemagick for more docs in DePolar Distortion.

1.3 Flip

magick trek-view-square-nadir-2.png -flip trek-view-square-nadir-3.png


Flip vertically.

1.4 Flop

magick trek-view-square-nadir-3.png -flop trek-view-square-nadir-4.png


Flip horizontally.

Step 2: Resize the nadir

The first step here is to obtain the image resolution (width x height).

Example nadir overlay guide

My example image is 1200x600.

So the nadir needs to be 1200 wide.

magick trek-view-square-nadir-4.png -geometry 1200x500! trek-view-square-nadir-5.png

Note the ! in the dimensions instructing Imagemagick to ignore aspect ratio. See the Imagemagick docs for more information.

Now the nadir is 1200px wide, and 500px in height.

My equirectangular image is 600 in height, so we need to reduce the nadir size (because our nadir is almost as large as the photo right now!).

Generally a nadir covers 10% to 20% of the photo. Let’s use 20% for this example.

600 (height of photo) * 0.2 (percentage size) = 120

Now we can resize the nadir to be 120 in height.

magick trek-view-square-nadir-5.png -geometry 1200x120! trek-view-square-nadir-6.png

Resized nadir

Step 3: Overlay the nadir

All that’s left to do now is overlay the equirectangular nadir created onto the photo.

We need to know where to place the nadir vertically. To calculate this; we know the photo is 600 in height and the nadir 120 in height, so:

600 - 120 = 480 (our vertical offset position).

composite trek-view-square-nadir-6.png GSAD0049-resize-1200.JPG -geometry +0+480 GSAD0049-resize-1200-nadir.JPG

Look down…

What’s great is that approach retains all metadata between source and final image.

Step 4: Script it

Now all you need to do is run the final command (step 3) on all your equirectangular photos to add the nadir (that is, assuming all your photos are the same dimensions and you want the same nadir size overlaid on each).

To save you some time here’s one we prepared earlier, our Nadir Patcher script.

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