14 Replies Latest reply: Feb 27, 2013 1:41 AM by c.pfaffenbichler RSS

    Problems converting layered rgb files with transparency to cmyk files retaining the layers.

    Bregnballe Community Member

      10.7.4/Mac Pro/PhotoshopCS6 13.0 - When cmyk converting a multilayered rgb file layers containing transparency doesn't convert to same profile as layers not including transparency, e.g. a product with a shadow - each on separate layers. the product layer is converted to working Color settings but the transparent layer isn't and is converted completely different, both grayscale and UCR/GCR.


      Any suggestions?

       

      Tom

        • 1. Re: Problems converting layered rgb files with transparency to cmyk files retaining the layers.
          davetwo Community Member

          Sorry. I'm not clear what you're saying. How are you doing the conversion Edit>Convert to profile? Then it will convert to the profile you choose surely.

          Do you mean it looks, different or is tagged differently?

          • 2. Re: Problems converting layered rgb files with transparency to cmyk files retaining the layers.
            c.pfaffenbichler Community Member

            The effects of transparency, blend modes etc. in different Color Modes can be vastly different; expecting a layered image to appear identically in RGB and CMYK is simply not sensible depending on the image content and structure.

             

            Could you please post screenshots to clarify your exact problem?

            • 3. Re: Problems converting layered rgb files with transparency to cmyk files retaining the layers.
              Bregnballe Community Member

              Hi Dave

               

              Maybe an example will clarify - if you make a new rgb doc with 3 layers, the bottom filled with white to se what's going on with the other two. Fill one layer with a gradient from black to tranparent, the other with a gradient from black to white and apply a layer mask to hide one half of each layer - then go Edit - convert to profile and you will notice that the transparent layer is converted completely different  - the graybalance is off and there's added a lot UCR so the black channel is a lot heavier.

              You can use Europe Prepress2, but any Color setting shows the difference...

               

              Tom

              • 4. Re: Problems converting layered rgb files with transparency to cmyk files retaining the layers.
                c.pfaffenbichler Community Member

                the transparent layer is converted completely different

                A black-to-transparent gradient Layer is basically solid black with added transparency.

                So however the RGB black is translated into CMYK is what it will then be – plus the effect of the transparency.

                 

                The black to white gradient on the other hand will be separated pixel for pixel according to the parameters of the new Color Space.

                • 5. Re: Problems converting layered rgb files with transparency to cmyk files retaining the layers.
                  davetwo Community Member

                  Not seeing anything dramatic from here... RGB version on top, cmyk on bottom...

                  Screen Shot.jpg

                  • 6. Re: Problems converting layered rgb files with transparency to cmyk files retaining the layers.
                    Bregnballe Community Member

                    Scary Dave - and you're sure one of those gradients are from black to transparent?Screen Shot 2013-02-14 at 13.12.06.png

                     

                    This is how mine looks - and it's the same on all Macs here...

                     

                    What's your set up?

                    • 7. Re: Problems converting layered rgb files with transparency to cmyk files retaining the layers.
                      c.pfaffenbichler Community Member

                      You seem to be misunderstanding the importance of Color Modes for the result of transparencies.

                       

                      In the CMYK Space I use black trasnslates to 87/78/64/92.

                      Half of that (as for example 50% transparency on a white background) is roughly 44/39/33/46.

                      A 128/128/128 gray (in eciRGB v2) on the other hand would translate to 49/40/38/26.

                      Edit: The CMYK space I used is ISO Coated v2 (ECI) (FOGRA39) by the way. 

                       

                      Also: FOGRA27 is obselete.

                      • 8. Re: Problems converting layered rgb files with transparency to cmyk files retaining the layers.
                        Bregnballe Community Member

                        In the example I just used the standard Europe Prepress2 setting which I don't normally.

                        To give you an idea of my dilemma this is what I'm working on:

                        Product images shot with natural reflections that I cut out to a separate layer, layermask added, blend mode multiply and with opacity as they need to be placed on coloured backgrounds in Indesign. Everything is rgb except for the final file that needs to be layered cmyk.

                        What annoies me is that when I merge the product group and reflection group and convert the file, the ref layer get's a different look than the product AND very different from my softproofed view  - even though grays in both have been desaturated equally.

                        What I don't get is why the graybalance isn't maintained just because there's tranparency...

                        That it get's darker is easily fixed but the graybalance isn't.

                        Long story - sorry...:-)

                        • 9. Re: Problems converting layered rgb files with transparency to cmyk files retaining the layers.
                          c.pfaffenbichler Community Member

                          If »black« is translated to A% cyan, B% magenta, C% yellow and D% black the result of plain transparency in the CMYK file (on white) is an according fraction of the four values.

                          The gray balance does not even enter into this.

                           

                          You should give up the misconception that layered RGB files should maintain their appearance when converted to CMYK (except in special cases).

                          • 10. Re: Problems converting layered rgb files with transparency to cmyk files retaining the layers.
                            davetwo Community Member

                            Yep, my lower 'Gradient fill 1' layer is black to transparent. Are you using a default black for the gradient (Command D)?

                            Working in CS6, my original file was created sRGB and converted to Fogra39 via Edit>Convert to profile. Using these parameters I cannot reproduce the shift you're seeing.

                            • 11. Re: Problems converting layered rgb files with transparency to cmyk files retaining the layers.
                              Bregnballe Community Member

                              Hi again to both of you...

                               

                              Sorry c.pfaffenbichler, but I'm not giving in - and as you have not really produced any facts to explain this I will see this as a Photoshop bug.

                               

                              @Davetwo - if you put those two gradients next to each other you WILL see a huge difference! Even on-screen the one is neutral gray, the other reddish.

                               

                              @c.pfaffenbichler - how can you state that graybalance has no importance here? Neutral grays turning red...?

                              and why does Photoshop convert transparents as it does? Using a huge amount of ucr and gcr with a huge amonut of uca...? almost like a generic conversion...

                               

                              but never mind...

                               

                              Soft proofing - going forward, how do we do this, knowing there's a flaw in Photoshop, not letting us see what transparents really look like when converted...?

                               

                              Tom

                              • 12. Re: Problems converting layered rgb files with transparency to cmyk files retaining the layers.
                                c.pfaffenbichler Community Member

                                Sorry c.pfaffenbichler, but I'm not giving in - and as you have not really produced any facts to explain this I will see this as a Photoshop bug.

                                If you make a simple two-point gradient in CMYK the gradient will (according to your settings) create a transition between the two colors.

                                If one of the colors is 87/78/64/92 and the other 0/0/0/0 then the resulting intermediate steps will depend on those two colors – the CMYK space’s GCR settings have no influence here.

                                Edit: To clarify: The CMYK space’s GCR settings determine how the default »black« is formed, but a gradient in CMYK is not dependent on those GCR settings. Otherwise all gradients would have to be dragged through the PCS and that would not make sense if somebody decides to make a gradient with certain CMYK colors.

                                 

                                And as I have tried to explain: A black to transparent gradient layer is basically a black layer with a transparency, so again: the CMYK GCR settings do not play into this.

                                Just convert a RGB black to transparent Layer to CMYK, rasterize it and then apply Layer > Layer Mask > From Transparency, then turn off the Layer Mask.

                                 

                                Whether you »give in« or not does not change the way these things are.

                                 

                                knowing there's a flaw in Photoshop, not letting us see what transparents really look like when converted...?

                                The flaw seems to be in your understanding, not in Photoshop.

                                Working in RGB and CMYK has relevant differences.

                                In RGB there is true black, in CMYK true black would have to be 100/100/100/100 which would violate the requirements for many or most processes.

                                And a CMYK space’s GCR settings are applied in conversion, when you yourself work in CMYK and commit a blunder (meaning things like exceeding the TAC, arbitrarily mixing grays, …) the problems are of your own making.

                                 

                                Edit: To restate: »expecting a layered image to appear identically in RGB and CMYK is simply not sensible depending on the image content and structure.«

                                The two color models are inherently different, the one additive, the other subtractive.

                                • 13. Re: Problems converting layered rgb files with transparency to cmyk files retaining the layers.
                                  c.pfaffenbichler Community Member

                                  Soft proofing - going forward, how do we do this, knowing there's a flaw in Photoshop, not letting us see what transparents really look like when converted...?

                                  Soft Proofing is not there for previewing what layered files would look like still layered in other color spaces.

                                  Your claim of a »flaw« is baseless.

                                   

                                  You should accept that RGB and CMYK are additive and subtracive models respectively and let go of your misconception that layered files should appear identically in both modes.

                                  The value of that assumption should be obvious from the fact that Blend If settings can be dependent on channels that are not there in the respective other mode.

                                  • 14. Re: Problems converting layered rgb files with transparency to cmyk files retaining the layers.
                                    c.pfaffenbichler Community Member

                                    An further example of why converting layered RGB files to layered CMYK files can be an extremely bad idea:

                                    rgbToCmykLayersScr.jpg

                                    For demonstration purposes I used ISOnewspaper26v4 which has a TAC of 240% (or thereabouts) because the display is more clear.

                                    Two overlapping black Layers set to Multiply in RGB can not get darker than 0/0/0.

                                    But in CMYK they can sum up to close to 300% TAC, which is in clear violation of that color space’s requirements.