16 Replies Latest reply on Jun 25, 2012 8:34 AM by Stella1251

    gaussian blur on a photo against gradient background

    Stella1251 Level 1

      Hi. Using PS CS4 on XP.

      I just got a job back from the printer company & I am noticing some lines that didn't appear on my print out here (on xerox color printer machine) to compare. I didn't really catch them on the proof either, but they used an epson proof and we printed on 100# gloss text stock for the final.

       

      What I have going on is a gradient background (using shape layer and gradient layer style effect) from a white to a light tan. Top to bottom on a regular Letter size sheet. In the upper right hand corner I have a image of a face that had that same light tan in the background. I faded this image into the gradient background by using gaussian blur. This is not very noticable in the file, but I can tell that it is there...you have to really focus your eyes to see it, but it's there, a line going around the image where the gaussian blur is. I'll attach a photo of the edge. I guess what I'm saying is it is not smooth - the image edges being blurred into the gradient background, but printed off a regular printer, it looks smooth. Is there anything I can do to prevent this in the future?

      Thank you for any advice. I'm considering no more gaussian blurs.............

       

       

      Untitled-1.jpg

        • 1. Re: gaussian blur on a photo against gradient background
          Noel Carboni Level 8

          That's a form of posterization - where you can see the differences between pixel luminance values. 

           

          It's possible that you caused it by the way you edit your images, since because of the gamma of most color spaces the actual luminance of actual adjacent luminance values is very close indeed.  For example, can you perceive any posterization in this image, which spans the same levels yours does?

           

           

          IsThisPosterized.png

           

          You can work at a higher bit depth when you're editing - e.g., 16 bits/channel.  That helps you to avoid ending up with visible quantization problems because most of the pixel math is done with greater precision.

           

          However, even when you use 16 bits/channel all selections are still only 8 bits/channel.  Layer masks are at the full bit depth, however.  You weren't quite specific enough about how "I faded this image into the gradient background by using gaussian blur" to comment on whether this could be an issue.

           

          Also, Dithering is a method that you can use in some cases.  It introduces slight noise to visually hide posterization.

           

          Lastly, here's a trick that can help ensure "hidden" things don't come back to bite you...  If you've got something in a part of an image that's difficult for you to see, in order to help you see more easily what's going on put an extreme Curves layer over the top.  You don't need to leave it there and visible, but when you have it on it can help you see better...  If you make the transition as smooth as possible with this much enhancement, it's sure to look better when it's viewed normally.

           

          LayerOverTop.jpg

           

          -Noel

          1 person found this helpful
          • 2. Re: gaussian blur on a photo against gradient background
            Stella1251 Level 1

            Hi Noel.

             

            Thanks for your response. I put a curves adjustment layer on. I moved the black slider all the way to the white slider. Both sliders are on the left side. I see the lines a lot better now.

            How do you dither in Photoshop (in the meantime I am looking this up)?

            I faded the image by using the guassian blur. How I did this was I selected the image by ctrl clicking on the layer, then I clicked the add vector mask button. Then I went to Filter>Guassian Blur. Then I unlinked the vector mask from the image and used the transform tool to scale down the blur. I may have used the eraser tool here and there, but I'm not sure..

            How did you make that image look so smooth? It looks great.

             

            Here is what I have with that curves layer put at the top of all my layers: (blurred the text on purpose)

            Untitled-2.jpg

            • 3. Re: gaussian blur on a photo against gradient background
              Stella1251 Level 1

              When I go to Posterize, the image edges still do not look smooth. Is this normal? I pull the slider the the right at 255 and that is how it looks now as above, when I pull it to the left at 2 the edge is hard.

              • 4. Re: gaussian blur on a photo against gradient background
                Noel Carboni Level 8

                It sounds as though you found the Posterize filter...   You don't want to add Posterization.  The effect you're seeing is called posterization, and it's what you're trying to avoid the appearance of.

                 

                When you work in 8 bits/channel, then the best you can get is 256 levels of gray, because every pixel color value is represented by 8 bit data.

                 

                If you create a smooth gradient then manipulate that luminance, because of round-off error in the 8 bit math you might end up with fewer than 256 levels - up to the point where you can actually see the level changes.  This is why I suggest doing your design work in 16 bits/channel. 

                 

                Then you'll want to do operations that use only 16 bit data (i.e., avoid selections, use masks instead for blending things).

                 

                I know this may be unclear; what you need to do is to try to gain an understanding of how your image data is represented in the computer, then it will all become more clear and you'll be able to get the best results you can.

                 

                -Noel

                1 person found this helpful
                • 5. Re: gaussian blur on a photo against gradient background
                  Stella1251 Level 1

                  Hi Noel. I changed it to 16 bit. I deleted my shape layer with the gradient overlay & remade another shape layer with a gradient overlay, but it still looks like the image above (bottom part of image going across.) not sure if that is supposed to help, but I tried.

                  Or do I need to recreate the whole thing in 16 bit?

                  I was using a vector mask to blend (I think [all black shown in the layer palette except the image shows a white area])..is there another mask I should be using?

                  • 6. Re: gaussian blur on a photo against gradient background
                    Noel Carboni Level 8

                    I have to admit I am having difficulty visualizing exactly what you're doing in your image based solely on your descriptions, so I find it hard to answer your direct questions about what you should do in your image.  Therefore I've been answering in general terms.

                     

                    Generally speaking with 8 bit data 256 levels of gray are usually *just* enough to hide posterization from view.  So if you're doing operations that can cause a reduction in levels - such as creating a gradient then manipulating it - that's why 16 bits/channel is good to use, because the math errors in the pixel manipulation won't be visible.

                     

                    If you're seeing posterization when enhancing your 16 bits/channel image then chances are you've already baked-in the posterization.  Just switching to 16 bits after the fact won't fix that.  Recreating the blending all in 16 bits (and remembering that I have said that selections only feather in 8 bits no matter what) should help.

                     

                    If you want to make a small crop of your image that highlights the problem available online, I'll be happy to open it in Photoshop and try to make more specific recommendations.

                     

                    -Noel

                    1 person found this helpful
                    • 7. Re: gaussian blur on a photo against gradient background
                      Stella1251 Level 1

                      Sorry Noel. I am going to attach an image (without text) of just the background and the photo I am having trouble with.

                       

                      Untitled-2.jpg

                      image without the curve layer at top. Having trouble with the gradient top to bottom as the background and on the left side of the image of the mans face.

                       

                       

                      Untitled-3.jpg

                      image with the curve layer at the top

                       

                       

                       

                      photo.jpg

                      original image of man

                      • 8. Re: gaussian blur on a photo against gradient background
                        Noel Carboni Level 8

                        The TIFF file made all the difference - the problem became obvious:  The mask is not pure black right at the edge of the image of the man.

                         

                        A slight curves operation on the mask covers up the edge.  Note that I've moved the black point slightly.

                         

                        BeforeCurvesOnMask.jpg

                         

                        AfterCurvesOnMask.jpg

                         

                        -Noel

                        • 9. Re: gaussian blur on a photo against gradient background
                          Stella1251 Level 1

                          hardvssoft.jpg

                          can I use the blur tool to soften that edge? or will it make it worse when printed? Just saw your other post, I ll take a look.

                          • 10. Re: gaussian blur on a photo against gradient background
                            Noel Carboni Level 8

                            One other thing that can confuse the issue...  Photoshop displays its downsized previews by combining layers in 8 bits, meaning if you're looking at a 16 bit image zoomed-out you might see what looks like posterization.  There's a way to get it to combine layers in 16 bits at any zoom level by setting Cache Levels to 1 in the Performance preferences - but this can drastically hurt performance and in CS5.5 and older also will expose some crash bugs (which thankfully seem fixed in Photoshop CS6).

                             

                            It's always best to judge effects at 100% zoom.

                             

                            -Noel

                            1 person found this helpful
                            • 11. Re: gaussian blur on a photo against gradient background
                              Stella1251 Level 1

                              Noel, I cannot thank you enough.

                              I'm grateful you were able to take a look at the file.

                              I notice a difference in comparing (at 100%) the previous file worked in 8 bit to the 16 bit after I added a new gradient background and put a new guassian blur on the image of the man.

                              The curves did help. that is something I will use in the future.

                              I still see a tiny bit of an edge so I might go over it with the blur tool. Hope that won't be a problem. Boy do I have a lot to learn!

                              • 12. Re: gaussian blur on a photo against gradient background
                                Noel Carboni Level 8

                                You're welcome, happy to help!

                                 

                                -Noel

                                • 13. Re: gaussian blur on a photo against gradient background
                                  Stella1251 Level 1

                                   

                                   

                                  Hey Noel, if you do a large backdrop, like a wall graphic for a trade show or something do you have to design those also in 16 bit? I imagine the file would be huge. I see that it doubles going from 8 to 16. I normally use a gradient background. I've never seen much of them in person (output in foreign countries), only a couple, but never noticed the banding lines..

                                  • 14. Re: gaussian blur on a photo against gradient background
                                    Noel Carboni Level 8

                                    No, not really, but you do have to be cognizant of when operations you do could result in the accumulation of error on 8 bit data.

                                     

                                    Back in the "bad ol' days" when so little in Photoshop worked in 16 bits/channel mode, folks got good at knowing which order to do things in (and in minimizing pixel changing operations) so that they wouldn't cause accumulation of round-off errors on the 8 bit data until it became visible.

                                     

                                    -Noel

                                    • 15. Re: gaussian blur on a photo against gradient background
                                      Stella1251 Level 1

                                      I will try to be a little more careful now!

                                      • 16. Re: gaussian blur on a photo against gradient background
                                        Stella1251 Level 1

                                        By the way Noel....the piece that we printed had to be changed anyway (lucky for me) so I was able to design in the 16 bit and add that curve layer on and fix the file as I did above....the piece came out great when reprinted. No hidden marks and no posterization!!!!