Could you please post the image (or a lores thereof)?
Duplicate the image, then adjust the channels so only the red or cyan/ green components remain, then use blending modes or an adjustment to merge the image into a greyscale by transforming the layers. Depending on whether or not the source image was shot in genuine stereo or just created using a post processing workflow, it won't align perfectly, though.
One could also
• use a Channel Mixer Layer to create the R-channel from a mixture if G and B
• use a (Smart Object) copy that is severly blurred and limited to affect the R-channel (in the Blending Options) and set to Blend Mode Color
But like Mylenium pointed out (parts of) the image will probably not line up – so it might be necessary to do some isolation/touch up to get a proper R-channel.
The image was originally a 2D image which was artificially broken into the red/cyan 3D version. So in terms of alignment, the two channels WILL align perfectly. However, from what I'm hearing from you and C, I'm going to lose the color -- it's going to become a grayscale image.
As per c.pfaffenbichler's request, here is a portion of the image.
Here is a link to the image
Am I right in my understanding that I lose all my color -- it becomes grayscale?
Thanks both of you for the input so far.
Bad luck – it would appear the image has been converted to another color space or otherwise edited so that all the channels are contaminated.
Just view them separately in the Channels Panel.