12 Replies Latest reply: Oct 11, 2011 8:02 AM by RenéG RSS

    Adjusting Black (K) while in RGB mode?

    adobe1kenobe066 Community Member

      Ok, so basically I'm wokring on an image in RGB mode, and I have my INFO box open, and I have the sample picker #1 and #2 set to display CMYK values.

       

      I'm not sure if many people realize that even if you're in RGB mode you can actually view other color information, including CMYK, within the INFO Box. If you click on the little Eye Dropper icons located within the INFO Box, it allows you to choose between different color info to be displayed, i.e. LAB, HSB, Grayscale, RGB, CMYK, etc, regardless of the color mode you're actually in.

       

       

      So I'm working on an RGB image, but I'm viewing the color info in CMYK, and my question is how do I directly adjust the K, or black, wihtin an RGB image, if I don't actually have the Black Channel available while I'm using Curves or Levels for example?

       

       

       

      I tried using the 'Brightness and Contrast' adjustment, but it affects everything else as well, not just the K/Black.

        • 1. Re: Adjusting Black (K) while in RGB mode?
          Chris Cox Adobe Employee

          You really can't control the K channel that way, because the K channel is calculated when you convert from RGB to CMYK.

          Unless you're already in CMYK, and know exactly what press conditions you will be using, you shouldn't be trying to mess with the K channel directly.

           

          You're better off just using Hue/Saturation to make the colors darker.

          • 2. Re: Adjusting Black (K) while in RGB mode?
            c.pfaffenbichler Community Member

            You really can't control the K channel that way, because the K channel is calculated when you convert from RGB to CMYK.

            What you could do is decide to use a different profile based on the same information but with a different GCR (if one is available or you have the software to create one yourself).

             

            And one cannot just view the CMYK-info but by using View > Proof Colors (and Proof Setup) one can preview the separated/converted image.

            • 3. Re: Adjusting Black (K) while in RGB mode?
              adobe1kenobe066 Community Member

              I'm not really trying to affect the 'Black Channel,' I know it's confusing. In fact, technically, there is no Black Channel to speak of, because I am in fact in RGB mode.

               

               

              Basically I was just trying to increase K, Black, in the INFO Box, from 0 to 4, under the #2 sampler, without affecting CMY. Because my INFO Box, is set to read CMYK values, but I am still in RGB mode. So I'm not really trying to affect the Black Channel, I'm just trying to affect what's being read as Black, while I'm still in RGB mode.

               

               

              Right now, it's reading C=11, M=42, Y=51, K=0, and I wanted to change K to 4 without affecting the other colors, without affecting C, M and Y. 

               

               

              I just wanted to see if that was at all possible.

               

              I don't think using another color profile is the path I want to go down. Right now I'm just using the standard sRGB.

               

               

              I actually had to look up GCR, grey component replacement, and I don't think that's what I'm looking for either.

               

               

              I just want to make a move in Photoshop that would accomplish changing the Black readout from 0 to 4 with out affecting CMY, or at least minimally affecting CMY.

               

              But I guess it's not really possible at all, using the adjustments and/or the blend modes? I've tried a couple of things and nothing seems to work really.

              • 4. Re: Adjusting Black (K) while in RGB mode?
                Jeff Schewe Community Member

                adobe1kenobe066 wrote:

                 

                I just want to make a move in Photoshop that would accomplish changing the Black readout from 0 to 4 with out affecting CMY, or at least minimally affecting CMY.

                 

                But I guess it's not really possible at all, using the adjustments and/or the blend modes? I've tried a couple of things and nothing seems to work really.

                 

                Have you tried Selective Color using Colors: Blacks and adjusting the Black adjustment?

                • 5. Re: Adjusting Black (K) while in RGB mode?
                  adobe1kenobe066 Community Member

                  I tried Selective Color beforehand.

                   

                  Black didn't affect anything but Neutrals did, but it had bascially the same effect Brightness Contrast had. It bought K from 0 to 4, but it also drastically affected CMY aswell.

                   

                  It's hard, or impossible, to affect Black, K, by itself, without affecting CMY while in RGB mode it seems.

                   

                   

                  I Guess I'm going to have to adjust everything in CMYK mode, becasue all my guides to color correct, whether it's skin, exteriors, products, etc., is based on CMYK.

                   

                  But there are advantages to staying in RGB, all your filters are available, and you retain all of the original color information you started with.

                   

                  It would be nice to fully color correct in RGB mode, while setting your Proof Setup to Working CMYK, and reading the INFO Box in CMYK. It's just adjusting Black, K, that seems to be close to impossible.

                  • 6. Re: Adjusting Black (K) while in RGB mode?
                    Chris Cox Adobe Employee

                    Because what you're trying to do makes no sense.

                     

                    It's like trying to flap your arms and see if it had an effect on the price of pork belly futures.  In some situations, it might, but most of the time it won't have any effect at all.

                    • 7. Re: Adjusting Black (K) while in RGB mode?
                      c.pfaffenbichler Community Member

                      Nice simile!

                       

                      So I'm not really trying to affect the Black Channel, I'm just trying to affect what's being read as Black, while I'm still in RGB mode.

                      You might be contradicting yourself or mixing terminology – »C=11, M=42, Y=51, K=0« would in pretty much any CMYK-space not represent what is likely to be perceived as »black«, so I am tempted to assume you are talking about the black channel.

                       

                      The GCR-settings in a CMYK-ICC-profile determine if and how much black will be used to represent a specific lab-value.

                      So it is possible that a color above to a certain brightness and saturation will simply not get any black, and darkening it may still not affect the black channel until it is very dark indeed.

                      • 8. Re: Adjusting Black (K) while in RGB mode?
                        charles badland Community Member

                        I Guess I'm going to have to adjust everything in CMYK mode, becasue all my guides to color correct, whether it's skin, exteriors, products, etc., is based on CMYK.

                        Where is the image going? Is it being prepared for 4-color offset press?

                        • 9. Re: Adjusting Black (K) while in RGB mode?
                          Community Member

                          You could switch to Lab color mode and affect contrast/levels/curves/etc on the L channel to enhance 'black'. Jumping between RGB and Lab color is not as destructive as going to CMYK.

                          • 10. Re: Adjusting Black (K) while in RGB mode?
                            Chris Cox Adobe Employee

                            >> all my guides to color correct, whether it's skin, exteriors, products, etc., is based on CMYK.

                             

                            Really?  Are you reading 20 year old instructions?

                             

                            CMYK is something you convert to at the last moment, right before going to press (and you convert for a specific press condition: paper, inks, gain, etc.).

                             

                            If you aren't going to a press, but using a desktop printer or preparing images for the web - then CMYK should be avoided completely.

                            • 11. Re: Adjusting Black (K) while in RGB mode?
                              c.pfaffenbichler Community Member

                              If switching to Lab I would recommend working in 16bit at least, though.

                              • 12. Re: Adjusting Black (K) while in RGB mode?
                                RenéG Community Member

                                Here is a little experiment you could do:

                                 

                                Place a Color Sampler (eyedropper) in a totally white area. Then: Selective Color layer > Colors: Whites > Method: Absolute and then move the black channel to the right and notice how much black you need to add to get a 4% K readout.

                                 

                                Or notice the CMYK readout when you add 4% black.

                                 

                                So, if you add 4% black using the method above, you will have what you're looking for: "change the K to 4 without affecting the other colors". But you're not gonna see it using the CMYK readout in the info palette, you'll have to change that readout to "K"

                                 

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