14 Replies Latest reply: May 5, 2012 2:50 AM by mantralightroom RSS

    How to select a color accurately?

    Adrtghhjj Community Member

      I have an image with lots of colors. I was wondering how could I select all the greens in the image.

      The problem is:

      - by "all the greens" I mean even those colors that have in their RGB values, Green as little as 1, even those  need to be caught in the

      selection.

        • 1. Re: How to select a color accurately?
          Trevor.Dennis MVP

          Go to the Channels Panel, and Ctrl/Cnd click the Green channel icon.  I'm interested in where you are going with this?

          • 2. Re: How to select a color accurately?
            c.pfaffenbichler Community Member

            Could you please post an example?

             

            You could load the green Channel as a Selection (command-clicking it in the Channels Panel), switch to Quick Mask Mode (Q), use Image > Adjustments > Threshold and switch back out from  Quick Mask Mode (Q).

            Maybe the Blend if-settings could provide another work-around.

             

            Edit: Ah, I probably misunderstood or rather misinterpreted; Trevor’s proposal may well suffice.

            • 3. Re: How to select a color accurately?
              Adrtghhjj Community Member

              I need that so I can erase the Green component out of every color in the image. I was curious how it would look afterwards.

              I have managed to select the green channel and make a selection from it but I don't know how to erase it, or parts of it.

              • 4. Re: How to select a color accurately?
                c.pfaffenbichler Community Member

                Just to make sure: Are you talking about the Green Channel in RGB (and do you comprehend what it means) or are you talking about the color perception »green«?

                 

                Could you please post an example?

                • 5. Re: How to select a color accurately?
                  Adrtghhjj Community Member

                  Could you please post an example?

                  As example, I have made a green gradient. The 1st (leftmost) color is pure green, the last (rightmost) is black. Inbetween, ever darkening shades of green.

                  I need that green gradient to be replaced with blue: all the *green* in the gradient should be replaced by darker and darker shades of *blue*, all the way to black.

                  The Replace Color effect in PS seemed to fit, but there you can only select the Source color (green) and then move the Hue slider in a not-so-accurate way. I need to be able to accurately select my Destination color (blue) too, as I need a specific nuance of blue.

                  • 6. Re: How to select a color accurately?
                    c.pfaffenbichler Community Member

                    You know one can post images on this Forum?

                     

                    If you create the gradient it would naturally be best to do so with a Gradient Layer and just edit that as needed later on.

                    But assuming this is not the case have you tried a Hue Adjustment Layer and selected »Green« (or if the image contains only the gradient keep it set to »Master«)?

                    • 7. Re: How to select a color accurately?
                      Noel Carboni Community Member

                      Adrtghhjj wrote:

                       

                      I need that so I can erase the Green component out of every color in the image. I was curious how it would look afterwards.

                      I have managed to select the green channel and make a selection from it but I don't know how to erase it, or parts of it.

                       

                      A point of confusion here may be that Adrtghhjj hasn't realized that all colors other than those made with combinations of pure red and blue contain some data in the green channel.  Christoph's question in post 4 is right on target, and particularly important to get a precise answer for.

                       

                      So, for example, note that the green channel of this orange-red color contains a non-zero green channel value, even though the color does not look green:

                       

                      SomeGreen.jpg

                       

                      -Noel

                      • 8. Re: How to select a color accurately?
                        Adrtghhjj Community Member

                        A point of confusion here may be that Adrtghhjj hasn't realized that all colors other than those made with combinations of pure red and blue contain some data in the green channel.  Christoph's question in post 4 is right on target, and particularly important to get a precise answer for.

                        Thanks for the info.

                        Yes, I was aware of that. I meant "all greens" as in "colors that contain a non-zero Green channel, even if the *color* green is invisible or barely visible".

                        E.g. I would consider color (R 255, G 1, B 255) as containing green.

                        In fact my original question concerned the process involved in making this color above reach the value of (R 255, G 0, B 255).

                        • 9. Re: How to select a color accurately?
                          Noel Carboni Community Member

                          Well, if you want to eliminate all green components you'd simply want to black out the green channel.

                           

                          If you want to add all the content of the green channel to the blue channel first, you could do that by cutting the green channel out (with black as your background color), then pasting it onto the blue channel and fading the mixing mode of the Paste operation to Screen or possibly Linear Dodge.

                           

                          More specifically:

                           

                          1.  Set background color to pure black.

                          2.  In the Channels panel, choose the Green channel.

                          3.  Select - All.

                          4.  Edit - Cut.

                          5.  Choose the Blue channel.

                          6.  Edit - Paste.

                          7.  Edit - Fade, choose Screen or Linear Dodge to add the pixel values you just pasted to what was already in the Blue channel.

                           

                          -Noel

                          • 10. Re: How to select a color accurately?
                            Adrtghhjj Community Member

                            How do I "black out the green channel"? I'm new at PS but I think this is what I've been looking for.

                            • 11. Re: How to select a color accurately?
                              Noel Carboni Community Member

                              I added some steps to the above post while you were responding.

                               

                              -Noel

                              • 12. Re: How to select a color accurately?
                                Noel Carboni Community Member

                                Adrtghhjj wrote:

                                 

                                How do I "black out the green channel"?

                                Another way is to go into the Channels panel, choose the Green channel, then Image - Adjust - Curves, and drag the white point all the way to black.

                                 

                                -Noel

                                • 13. Re: How to select a color accurately?
                                  Adrtghhjj Community Member

                                  Thanks. This has solved the problem.

                                  • 14. Re: How to select a color accurately?
                                    mantralightroom Community Member

                                    nice very nice

                                     

                                    sadly there is no option to bookmark the cool topic