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How do I Rebuild the Red Channel?

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  • How do I Rebuild the Red Channel?

    So I recently got a bunch of photos with all kinds of problems. I tore through the whole lot of ‘em with little to no problem. Then, I got to these two and have pretty much hit a brick wall. I have tried the technique for utilizing info from the better channel (the green), but honestly I have never gotten that to work properly. The most success I have had so far was with manually editing the red channel. But this is tedious and hasn’t produced any results worth sharing. So my main problem here is that the red channel is so blown out and channels are the one thing I use the least and therefore, understand the least. I tried to search for tips and the like but I’m really not even sure what the technical name for this problem is. So I have been sifting through tons of generalized stuff on the net. At this point I’m ready to call it quits, but I figured that before I threw in the towel, I should see if anyone here can give me some advice.

    I’m using CS by the way.

    Thanks in advance. Really, any help is appreciated.
    Attached Files

  • #2
    Hi there, Jimmy. welcome to RetouchPRO

    (for the first image)
    You are (a wee bit) lucky in that the Red channel is not completely lost. However it does need a good work over.

    This is what I did:

    1) Using the Channel mixer, make a new greyscale layer (option monochrome) using 50% green and 50% blue (let's call this GB from now on);

    2) Turn of GB for now, and make another new greyscale layer from just the Red channel (100%) and run AutoLevels on this;
    - This channel is very noisy but it will still be useful for indicating the red / not red areas. So let's salvage what we can.
    3) This Red channel is more blown out at the edges. Run the HighPass filter with a big radius (+-200) to even things out some;

    4) Now let's take out some noise. Run Median until the worst noise is gone and then Smart Blur which will blur and sharpen at the same time.
    We now have a vague blotchy Red channel

    5) Remember the GB layer? Turn it on now and put our new Red channel layer above it with blending mode set to Overlay (this combines the Red / not Red information with the details from the GB layer);

    6) Combine this to a new layer (<Ctrl><Alt><Shift><E>) and in the Blending Options unmark the G(reen) and B(lue) channels leaving only the R(ed). The Green and Blue channels will come from your original.

    7) Combine this to a new layer again, and run the AutoLevels (<Ctrl><Shift><L>) and the image should spring to life.

    Hope this helps a bit.

    Attached Files

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    • #3
      I tried working with this but had too many interruptions to get very far. So I'm here to say...Great work Ro. No smiley for a pat on the back, so here is a virtual one.

      Janet

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      • #4
        wow Ro, very good!
        ~Nancy~

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        • #5
          Rô -- very interesting, and successful strategy!

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          • #6
            Hi Rô

            Thank You So Much for Your Method. It works perfectly and shows a great understanding of the tools you are using, and why.
            This should be a tutorial. It would be a shame if it got lost in the other threads.

            The only step I did not get was the High Pass to even thing out. I must do some more reading. But I have saved this to refer to in the future.

            I was going to give this thread five stars but then I realised that you did the easy one.


            Ken
            Attached Files

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            • #7
              byRO it's funny I love to turn the channels on and off like you mentioned here. I don't run across a lot of people that use this method of replacing channels.. Very powerful... I find most copy and pasted back into the channels..

              By the way I reccomend instead of merging in step 6 create a group and then uncheck the GB of the group and put the two layers in the group . This way you can adjust things without having a merge ( i try to avoid these at all costs) Maybe it's just me though..

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              • #8
                Ro, that's a neat solution. Turns out the image of the boy lends itself to another quick solution to bring it back into an acceptable range.
                I converted to LAB. Then Ctrl 2 to select the A Channel. Next Ctrl I to invert it. Now back to RGB Color and a quick Levels adjust to attenuate the Green channel. I stopped here but if I wanted to spend more time on the image I would tone down the deep green around the sides and adjust the skin tone which is a bit flat. Regards, Murray
                Attached Files

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                • #9
                  Originally posted by Cameraken
                  The only step I did not get was the High Pass to even thing out.
                  Ken, if you look at the Red channel you see that there are large areas on each side which certainly are lighter due to fading and are not part of the image. The fact that they are large areas is what makes things easier because we can "filter" them out.
                  Imagine a process like the one in the attachments....
                  1) The original Red channel;
                  2) A Gaussian blur, radius 60;
                  3) The original + the inverted Gaussian blur (blending Linear Light 50%).
                  If you remember the relationship between the Gaussian blur and the High-pass filter you'll see that these three steps correspond exactly to the application of the High-pass filter at the same radius.

                  Originally posted by Cameraken
                  I was going to give this thread five stars but then I realised that you did the easy one.
                  He,he, he - you get me there!

                  Attached Files

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                  • #10
                    Yes, this one is much more difficult.....

                    1) To fabricate a mask for the correction, I used the Channel Mixer to make a greyscale image from 100% Red and -45% Green. This mixture cancels out the features leaving a fairly good image of the streaks (see attachment 1 - inverted). I used a fairly large Median filter to clean this up and make a mask;

                    2) Curve adjustment on the Red channel using the mask above (attachment 2); (this didn't look too good so...)

                    3) Another curve adjustment using a soft brush manually applied on the mask (attachment 3);

                    4) Almost there now. Applied some standard image enhancement tricks to finish up (attachment 4)


                    (PS: Ken, U O me *****)
                    Attached Files

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                    • #11
                      Hi Rô.

                      OK. OK You got Your Five stars. Great job. You got some detail in her ear rings which I missed.

                      Thank You for the extra info on High Pass.

                      Image Invert > Gauss > Blend Mode Add.

                      This (if I am not mistaken) is the same as a contrast reduction. So this is similar to a balance of Shadow/Highlight. Yes?


                      Ken

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                      • #12
                        Hi Ro, super job on the tough one. FYI, I found a way to get to your 3rd stage quickly without a mask. With the original image, duplicate the red channel as is and apply the copy to the red channel in multiply mode 100% opacity. Then apply the copy again to the modified red channel. This will get you exactly to your 2nd attachement. Next select the entire left side of the image from the separation (with a heavy feather) line down the gentleman's shirt. I took the image into LAB and with two very simple straight line curves, moved the A & B channel to get the color on the left half of the image to match. The L channel looked really nice. I attenuated the heavy yellow cast in the face with a narrowly restricted B channel curve. Finally, blurred the A & B channels to get rid of a little color noise. I stopped here since you already applied the image enhancement tricks
                        Regards, Murray
                        Attached Files

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                        • #13
                          as ken pointed out, this is the easy one

                          this was mostly 'color balance', 'color mixer', a blank raster layer for fill here and there, and splitting out the red channel and erasing the noise rather than blurring it, then adding the channel back and tweaking it some more. i also ran a 'digital camera noise removal' and added a contrast adjustment layer.

                          the image is primarily a blue and green image. lots of grass and lots of sky. the oddity here is the boy's skin. but that's influenced greatly by the surrounding blues and greens and the natural shading and colors would tend to dull down the pinks and reds. so, in the color balance and color mixer steps, i pretty much removed ALL the red, except in the high tones. and that removed the color cast of the warped red channel. the rest was just in trying to get the boy's skin a bit less blue and green and sharpening and tweaking a bit.

                          if i were doing this for a client, however, the first thing i'd do is crop the image and get rid of that bright foreground and remove the extraneous side wasted space. this would also eliminate most of the unwanted reds which were heaviest on the sides and that alone would reduce the work and make this easier to do.

                          craig
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                          • #14
                            Wow.

                            This is one freakin' great thread. This is exactly one of the things I want to get better at. I've bought entire books and got less out of them than I just learned. (did that sentence make sense?)

                            Ro, Ken, Murray - hats off.

                            David

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                            • #15
                              Hi David.

                              Thanks. Yes Rô’s steps were great and I always enjoy reading Murray’s LAB approach.

                              In the ‘hard one’ I got to Rô’s attachment 2 picture without a mask. I just used channel mixer
                              Red +46
                              Green -56
                              Blue -24

                              In the ‘easy one’
                              I had some success with apply image after Rô’s step 4.
                              Channel Red blend mode Multiply (Attached.)


                              Ken
                              Attached Files

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