How To Do An Infrared Channel Swap in Adobe Photoshop

How To Do An Infrared Channel Swap in Adobe Photoshop

In this article, I will explain how to do a channel swap for an infrared photo using Adobe Photoshop. If you are an Affinity Photo user, the process is similar and documented in another of my articles. But let’s start with a couple of reasons why you might want to perform a channel swap in an infrared photo:

1. To produce better colours or change the colours.
2. To improve the processing when converting an infrared photo to black and white.

An Infrared Photo Myth

We also need to dispel a common myth which is that “you must do a channel swap when processing infrared photography”.

This just isn’t true. When you are processing colour infrared photography, the biggest factor in producing good colour is setting the White Balance correctly. If you don’t set a good White Balance, you will typically end up with a photo like this (1) when you open the image in Lightroom, Photoshop or many RAW editors.

But when we correct the White Balance, we see very different photo (2). How to do this is quite a big topic so we will need to leave that for another article

Having sorted out the White Balance, let’s look at how to make the Channel Swap.

Channel Swap Using the Photoshop Channel Mixer

Start by opening the infrared photo in Photoshop that you want to use for the channel swap.

Next, add a Channel Mixer Adjustment Layer to the image. You can do this in the Photoshop Adjustments Panel by clicking the Channel Mixer icon. Alternatively, click the “Layer” menu item at the top of the Photoshop interface, and go to the “New Adjustment Layer” sub-menu. There you can click the “Channel Mixer…” option to add the layer.

You should now see the new Channel Mixer Adjustment Layer added to the image in the Photoshop Layers Panel. When this is selected, you will see the Channel Mixer controls displayed in the Photoshop Properties Panel, as shown below.

In the Channel Mixer controls, you will find a dropdown for the “Output Channel”. We use this to choose which of the colour channels we want to adjust in the image. As our infrared photo uses the RGB colour format we will see the options Red, Green and Blue in the dropdown.

Notice that we don’t see an Input Channel in the controls. This is because the Input Channels are the channels in the original image. When we have the Output Channel set to Red, it means we are adjusting the Red channel of the original image to produce a new colour.

Adjusting the Channel Mixer

When making a channel swap, we are swapping two colour channels of a photo. A common example is a Red/Blue channel swap where we swap the red and blue channels. This causes the red to turn blue in the image and blue to turn red.

We will start by selecting the Red channel. When this is selected, you will see the Red colour slider at 100% and the other sliders at 0%. This tells us that 100% of our infrared photo’s Red channel which appears as red in the output.

The way that we can swap this to be blue using our Channel mixer is to set the Red slider to 0% and the Blue slider to 100%. You can see this below.

This however is only half of the process because we have only swapped red for blue in the Red channel. We still need to do the Blue colour channel to complete the effect.

Swapping the Red and Blue Colour Channels

To swap the colours in the Blue colour channel, click the Output Channel dropdown and choose Blue from the list. You will now see the Blue slider at 100% and the other sliders at 0%. This tells you that the Blue channel is Blue and so we need to swap it for red.

To do this, set the Blue slider to 0%. Then move the Red slider to 100%. You can see this and the result below.

This is what is known as a Red/Blue channel swap because we have swapped the colours in the two channels.

Finishing the Infrared Image

Having completed the Red/Blue channel swap of our image, it now appears a little dark. We can easily correct this by adding a Levels adjustment to the image. You can see the finished result below (1).

The other two versions shown in the illustration also use the same Red/Blue channel swap using the Photoshop Channel Mixer. The different colours were achieved by adjusting the White Balance in the image. In image 1, the White Balance was set by sampling the tree trunk. In image 2 it was set using the Grass, and in image 3 it was set using the cloud in the sky.

Final Points About Colour Infrared Photography

 The process of channel swapping for infrared photography is often referred to as false colour infrared photography. This isn’t however entirely accurate. Technically, infrared light doesn’t have a colour because we can’t see it. What we know as colour is created when our brain interprets different wavelengths of light to be different colours. As we can’t see infrared, it doesn’t have a colour associated with it.

What really creates the colour (or false colour) is assigning a white balance. All the channel swap has done is change which colour is displayed. This is what made the sky blue rather than red and the foliage red rather than blue.

If you’re interested in infrared photography, read this article which explains the essentials.