20 Replies Latest reply: Mar 29, 2014 1:58 PM by sPretzel RSS

    Save as JPEG changes CMYK colour

    sPretzel Community Member

      Hi,

       

      I have a solid colour in Photshop that I set CMYK values for (I work in CMYK image mode). When I save as JPEG, the resulting JPEG file changes one of the CMYK values by 1 percentage point. When I save as TIFF, it works fine (CMKY values match original photshop file). What is going on?

       

      This is for CS4.

       

      Thanks.

        • 1. Re: Save as JPEG changes CMYK colour
          Chris Cox Adobe Employee

          Yes, JPEG is a lossy file format -- you won't get the exact values out that you put in.

          • 2. Re: Save as JPEG changes CMYK colour
            sPretzel Community Member

            Thanks Chris. But I get the right value (same value) in other files with the same background. Is there a way to force the right value in JPEG? Even if I only keep the solid background layer and save as JPEG, it changes that value by 1 percentage point. I don't expect JPEG to lose this kind of information!

             

            My initial file is in JPEG (+ other layer of solid colour in Photoshop). What do I gain from saving in TIFF?

            • 3. Re: Save as JPEG changes CMYK colour
              Chris Cox Adobe Employee

              No, there is no way to force a value in JPEG - again, it is a LOSSY format -- you will almost never get the same values out as you put in, they will always be off by a little bit.  If you don't want values to change, save in a file format that preserves exact values (like PSD, TIFF, etc.).

              • 4. Re: Save as JPEG changes CMYK colour
                david k Community Member

                Not to contradict Chris, but did you set the jpeg to 0% compression? It may still change the color, but its worth a try.

                • 5. Re: Save as JPEG changes CMYK colour
                  Curt Y Community Member

                  There is no such thing as 0% compression with jpg, but at setting 12 it is the least.

                  • 6. Re: Save as JPEG changes CMYK colour
                    sPretzel Community Member

                    I set it to setting 12 as Chris said. I also tried saving in all three types Baseline standard, optimised, progressive (all with setting 12). Same result! I even saved a page with only a solid background in that colour...and it still changes it. It must depend on the page size. TIFF saves correctly (but note that in other canvas sizes, jpeg also saved the colour correctly). I resorted to TIFF in the end.

                     

                    By the way, if I have an image saved from Photoshop in setting 12 jpeg, then I reopen it in Photoshop and resave the same image (no modification) in setting 12 jpeg, would I still lose data in the file?

                    • 7. Re: Save as JPEG changes CMYK colour
                      D Fosse Community Member

                      Jpeg is recompressed - based on the previous compression - every time you save it, no exception. IOW it's cumulative.

                       

                      And since every new save introduces new artifacts, file size tends to increase with every new save, at the same quality setting.

                       

                      Jpeg is really not a working file format. The only reason it's still widely used is the extreme reduction in file size, useful for online transport and storage. The file should be saved as jpeg exactly once at the very end, and then sent off.

                      • 8. Re: Save as JPEG changes CMYK colour
                        sPretzel Community Member

                        Thanks twenty_one. That's good to know. I imagine it wouldn't hurt the file further if I process a jpeg image and then save in a lossless format like TIFF.

                        • 9. Re: Save as JPEG changes CMYK colour
                          david k Community Member

                          sPretzel, I assume you're starting with a jpeg image. As part of my workflow, I usually start by doing a 'save as' and save to the native Photoshop format, which means I can work with (and save) the image using all the tools (layers, filters, transformations, etc) available in PS, continuing to save along the way.

                           

                          As an aside, what are you planning to ultimately use the image for? Inkjet printing,? The web? Publication? This will guide your decision on what you could end up doing as a final 'save as' on the image.

                           

                          And I'm curious, are you only using the CMYK 'palette' to select your colors, or are you actually working in the CMYK color space or profile?  If the latter, you should know that some file formats don't support CMYK, and neither do web browsers.

                          • 10. Re: Save as JPEG changes CMYK colour
                            david k Community Member

                            Agreed, I meant the least amount of compression possible, though it seems it will still change the image no matter.

                            • 11. Re: Save as JPEG changes CMYK colour
                              sPretzel Community Member

                              Hi david k. That's right, I start with a jpeg file. I go to print. I am using a colour profile in the CMYK colour mode.

                              It is often said that jpeg is not a good format for print, but I assume that if I start with a jpeg file and don't do any changes to it, then that original jpeg file is as good as it gets for print, right? (i.e. no need to save in another format)

                               

                              I was surprised by jpeg's behaviour where it takes one colour data just to replace it with another colour data. It doesn't make sense to me. If it can hold one set of CMYK values, why can it not hold another set of CMYK values instead (I'm referring to a file with only a solid background colour)?

                              • 12. Re: Save as JPEG changes CMYK colour
                                david k Community Member

                                I'm confused. If your goal is to print the image, why not open the jpeg in Photoshop, do a save as using the native .PSD Photoshop file format, and just continue to work and save in that file format? Going back to jpeg makes no sense.

                                 

                                In the first place, Jpeg does not support the CMYK color space, so every time you save it, it will save in the much smaller sRGB space. Also, between this and the fact that it compresses the image even at the highest settings, you are going to get changes in the image, including in the colors.

                                 

                                Just avoid all this and work in .PSD file format.

                                 

                                Another point: all of the photographers I know usually work in an RGB color space, Adobe rgb for example. As I understand it, CMYK is used in graphics and publication, often because you want to split the image into four channels to use in commercial four-color offset printing.

                                 

                                If you're going to be doing inkjet printing, or via a service, I'd suggest staying in an Rgb workspace--you can still decide to use the CMYK menu to select your colors.

                                 

                                Color management can be tricky, so I'd suggest you do a bit of research.

                                • 13. Re: Save as JPEG changes CMYK colour
                                  sPretzel Community Member

                                  I ultimately saved as TIFF. I have experienced some issues importing PSD files in other applications. It is my understanding that JPEG does support CMYK (I would think that Photoshop wouldn't allow to save in that format if JPEG didn't support CMYK). See this thread for example: http://forums.adobe.com/thread/795849

                                  • 14. Re: Save as JPEG changes CMYK colour
                                    D Fosse Community Member

                                    That thread sums it up well. No problem with CMYK support in the jpeg file format itself, any issue is with jpeg readers.

                                     

                                    If this is going to offset press, the recommended workflow is RGB for photographic material. It'll most likely end up in an InDesign file, converted to destination CMYK on press-ready pdf export. Do you know for certain that your CMYK profile is the one that will be used? If you just rely on the Photoshop default (US Web Coated SWOP) you may be in for a surprise.

                                    • 15. Re: Save as JPEG changes CMYK colour
                                      sPretzel Community Member

                                      I actually send out a pdf. It does the conversion to CMYK for me, as you pointed out. In this case, I've done conversion to CMYK for some of the graphics prior to printing to press-ready pdf (which converts to CMYK anyway) - I suppose it would have made sense to leave what was in RGB in RGB and do any conversion at the very end, unless conversion to CMYK without touchups at the very end did not look good. I'm using the profile the print shop recommended.

                                      • 16. Re: Save as JPEG changes CMYK colour
                                        D Fosse Community Member

                                        Then all is well, as long as you know the final CMYK

                                        • 17. Re: Save as JPEG changes CMYK colour
                                          sPretzel Community Member

                                          It seems this is another problem. I type a value in CMYK in the colour panel, fill an object with it (in Photoshop), and the INFO panel reads a different value: sometimes the same, sometimes off by 1 percentage point. This is before even saving the file, simply in Photoshop.

                                          • 18. Re: Save as JPEG changes CMYK colour
                                            david k Community Member

                                            What's your work flow at this point? Are you working with a .psd file?

                                             

                                            I suggest you work in Adobe RGB color space with a .PSD file and do your conversion to PDF (or whatever) at the end of all your other changes, following the directions given to you by the print service. Stop working with a JPEG file if you still are. 

                                             

                                            As to the color change, though this might be frustrating, you keep describing it as either 1% or not happening at all. Can you actually see the change in the image? I'm thinking that this small a change will not be visible to the naked eye, certainly not on your monitor or in a printed book; if that's true, why make a big deal about it?  

                                            • 19. Re: Save as JPEG changes CMYK colour
                                              D Fosse Community Member

                                              That has to be noise (or jpeg artifacts). Try to set your eyedropper tool to read 5 x 5 average instead of point sample.

                                              • 20. Re: Save as JPEG changes CMYK colour
                                                sPretzel Community Member

                                                No, it's not noise. Instead of using the background fill created in Photoshop, I brought in the same background colour from Illustrator (as a smart object in Photoshop). Now the jpeg saves with the correct CMYK values!