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Question

RGBI Image in Photoshop

Forum|Forum|9 years ago
March 2, 2017
5 replies
2261 views

How would I open an RGBI image (the I being infrared) in photoshop so it will display correctly?

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tylerr61376702Author

Participating Frequently

Finally got it. I had to completely delete the blue channel and then change the Alpha to the red channel. Thanks for the help.

tylerr61376702Author

Participating Frequently

Thanks for the quick response. I made a channel mixer adjustment layer and switched the green to blue, red to green, and turned off the blue. The infrared was already red. This is what I got. I was able to adjust the levels for the Alpha (Infrared) channel but for the other channels, the adjustments are grayed out so I can't change the levels. I still feel like I'm missing something.

D Fosse

Community Expert

Not sure what you mean by "the infrared was already red". You need to copy the infrared data out of the alpha channel and into the red channel.

Then turn alpha channel visibility off. You can't use the alpha channel as such - it's just for carrying the information.

tylerr61376702Author

Participating Frequently

I have opened it in Photoshop but it is displaying a normal RGB image. When I open up the Channels, there is a fourth channel called Alpha 1 that is turned off. If I turn it on, it adds red to the image but does not look the way it should. See image below. I do have a low res image from the supplier of the image of what it should look like and we have opened it in a photogrammetric mapping software where it displays correctly. See second image below. I have messed around with the channels in Photoshop, turning some on and off, but nothing looks right.

D Fosse

Community Expert

The alpha channel looks like it carries the IR information, so you have all the data you need in that file.

However.

There is no correct way to display four channels in a three channel medium. Monitors, desktop printers, they all have three color channels, R, G and B. You can't simply add a fourth channel. Even CMYK is based on three color channels - the fourth channel is just to provide contrast and depth.

So there are some conventions to get around this. The most common way to do it is known as "IR false color". What you do here is shift all channels one step sideways. Here's how:

Copy the green channel content and paste it into the blue channel.
Copy the red channel content and paste it into the green channel.
Copy the infrared content (from the alpha) and paste it into the red channel.
Throw away the original blue channel.

It looks like that's what was done in your second example.

Note that there is no reference for brightness or contrast in the IR channel. You can't see it, right? So you'll get the most information out of the finished file if you simply try to balance it against the other two channels. Set the black and white endpoints consistently, and adjust midtones to taste. This is fairly quickly and easily done with Levels.

D Fosse

Community Expert

What do you mean by "correctly"? There is by definition nothing "correct" with IR, since you can't see it.

But technically, such a file could be either Multichannel, or CMYK, anything with four channels. I suppose RGB + alpha channel could also work, just for storing the data.

If the file has been saved in a standard way, Photoshop should be able to open it. Just don't expect any correct way to display it, because there isn't one.

Sahil.Chawla

Adobe Employee

Hi Tylerr,

All the images can be opened in Photoshop the same way by going to File > Open.

Have you tried opening it?

Regards,

Sahil

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