How do I add together two a⨯a images to a single 2a⨯a image in the compositor?

Question

I've tried using the translate node to move each image a/2 px left or right, but it cuts off the image.

To illustrate, here's an image:

What are you talking about? Could you please edit the question and clarify what you mean, provide some context maybe and add some pictures. It's unclear what the problem is and what your goals are. — Martynas Žiemys, Apr 09 '20 at 22:37
If I understand correctly, you have two square renders of size a, and you are trying to composite them side-by-side into one image of size 2a by a, is that correct? — TheTrueJard, Apr 09 '20 at 22:41
related https://blender.stackexchange.com/questions/52231/rendering-a-stereoscopic-image-in-blender-2-77/57870#57870 — Duarte Farrajota Ramos, Apr 10 '20 at 16:44

score 4 · Accepted Answer · answered Apr 09 '20 at 23:42

4

I suggest a different solution:

here's the Compositing setup:

The first node (image node) is an empty image (generate in blender as 100% alpha image) with the full size of your output image (1024x512). When the alpha image is added to the rendered image, the output (file output) is a 1024x512px file.

Add the second scene (again translated in the opposite direction) and you'll have the two renders aligned.

answered Apr 09 '20 at 23:42

Sanbaldo

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This approach is much better than my answer. Will the Composite output also stretch to the dimensions of the generated image, or does that only work for file outputs? – TheTrueJard Apr 09 '20 at 23:52
1

only file output (as far as I tested). – Sanbaldo Apr 09 '20 at 23:58
Thank you very much! Can I make the empty image in blender? – schuelermine Apr 10 '20 at 01:16
image node, new, than follow the screenshot:
https://i.imgur.com/J4FG4Uq.png
– Sanbaldo Apr 10 '20 at 01:32

score 0 · Answer 2 · edited Apr 09 '20 at 23:58

This is a bit of a hack and requires you to change a camera setting, but it gets the job done:

Create a new scene and set its output resolution to something with a 2:1 aspect ratio (such as 1024x512, if the original images are 512x512). Add the two inputs as Render Layers.

The issue here is that when you render, the two images will be rendered with the same aspect ratio as the current scene (2:1) instead of the aspect ratio of the scenes they were created in (1:1). To get around this, we have to render the inputs twice as wide as the output results will be (because parts of it get trimmed off), and trim off whatever's left.

Set the cameras to be exactly 1/2 the original focal length in the camera settings in the properties panel. (Ex: if they were the default 50mm before, change them to 25mm).

cameras

(The image shows both the original and new focal lengths, for clarity.)

Rendering these from the new scene will crop off the top and bottom edges when it changes the aspect ratio. Then, in nodes, you can translate them as necessary and combine. The Box Mask node crops the left side of the topmost image so it doesn't overlap with the one next to it.

(Here you can also see that the top and bottom were cropped off, hence why we needed to increase the focal lengths)

Result:

result

How do I add together two a⨯a images to a single 2a⨯a image in the compositor?

2 Answers2