12 Replies Latest reply on Mar 7, 2017 2:17 PM by davescm

    RGBI Image in Photoshop

    tylerr61376702

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

       

      [Moderator:  Moved from non-technical Lounge to Photoshop General Discussion.]

        • 1. Re: RGBI Image in Photoshop
          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

          • 2. Re: RGBI Image in Photoshop
            D Fosse Adobe Community Professional & MVP

            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.

            • 3. Re: RGBI Image in Photoshop
              tylerr61376702 Level 1

              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. Alpha_Channel_Turned_On_Photoshop.jpgCIR_Screenshot.jpg

              • 4. Re: RGBI Image in Photoshop
                D Fosse Adobe Community Professional & MVP

                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.

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                • 5. Re: RGBI Image in Photoshop
                  tylerr61376702 Level 1

                  Photoshop_Channel_Switch.jpg

                  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.

                  • 6. Re: RGBI Image in Photoshop
                    D Fosse Adobe Community Professional & MVP

                    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.

                    • 7. Re: RGBI Image in Photoshop
                      davescm Adobe Community Professional

                      That red you are seeing when you turn on visibility of the Alpha channel is just the ruby overlay Photoshop uses to show the Alpha channel when it is used as a mask. It does not print.

                       

                      To get the 4 channels into 3 follow what D.Fosse advised

                       

                      Dave

                      1 person found this helpful
                      • 8. Re: RGBI Image in Photoshop
                        D Fosse Adobe Community Professional & MVP

                        BTW it would be really neat if this could be done with a channel mixer adjustment layer - but unfortunately it only operates on the RGB channels. It won't source alpha channels. Hmm, might make a good feature request...

                        • 9. Re: RGBI Image in Photoshop
                          tylerr61376702 Level 1

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

                          • 10. Re: RGBI Image in Photoshop
                            davescm Adobe Community Professional

                            https://forums.adobe.com/people/D+Fosse  wrote

                             

                            BTW it would be really neat if this could be done with a channel mixer adjustment layer - but unfortunately it only operates on the RGB channels. It won't source alpha channels. Hmm, might make a good feature request...

                             

                            Instead of channel mixer you could use Calculations to create new channels - combining the existing channels into new channels and then copying them back into into RGB.

                             

                            As a simple example you could leave blue and green alone then combine Red and IR. To this by using calculations to Add the Red Channel to the IR channel (with a scale of 2 to stop it blowing) and create a new channel. Then copy this across to Red.

                            That way Red becomes an combined Red+IR.

                             

                            All manner of combinations are possible - not as convenient as the channel mixer - but available now.

                             

                            Dave

                            • 11. Re: RGBI Image in Photoshop
                              D Fosse Adobe Community Professional & MVP

                              Yeah, I could try that.

                               

                              I do this frequently in my job at the art museum, it's used quite a bit in conservation and research. The main problem is to establish standardized procedures, harder than it would seem in fact, precisely because there is no visual reference. A lot of it is chasing moving targets. We use sheets of polytetrafluoroethylene - teflon - for white balancing, because it has equal reflection in all wavelengths. So it should theoretically be "white" even in invisible light, both IR and UV. But it doesn't always work out that way.

                               

                              It's very interesting work. It can really bring out the invisible and make it visible. I also understand that it's useful in agriculture, for vegetation analysis.

                              • 12. Re: RGBI Image in Photoshop
                                davescm Adobe Community Professional

                                It does sound an interesting, and challenging, branch of photography. I have enough trouble getting to print what I can see, let alone what I can't

                                 

                                Dave