8 Replies Latest reply: Jun 23, 2013 6:55 AM by Stan Patz RSS

    Real streaks or screen artifacts?

    Stan Patz

      I am using CS6, but this applies to all past versions.

       

      When I use a feathered Brush (or Gradient tool, or Eraser, etc.) on a toned background, upon close inspection I see streaks or posterization. The flaws in the gradient appear to persist at any screen magnification. The question is, are these marks real or screen artifacts?

       

      Even though this is a good theoretical question, I am working on a full page ad for magazine reproduction. The art director asked for a full bleed so about 60% of the page will be something I am creating. Will the subtle marks I now see on this background appear in print - magazine repro, probably 133/line screen?

       

      (And, no, I do not want to add noise to the background because it will not match the grainlessness of my digital image.)

       

      Stan Patz

        • 1. Re: Real streaks or screen artifacts?
          the_wine_snob Community Member

          Can you attach, or link to the Image, so that others can see what you are seeing?

           

          Good luck,

           

          Hunt

          • 2. Re: Real streaks or screen artifacts?
            Stan Patz Community Member

            Dear Bill,

             

            Thanks for replying so quickly.

             

            The streaks I see in my image are pretty subtle. They are easier to see in PS when I grab the image and gigle it side to side. Way back in my darkroom days, when a bw print came off the dryer too quickly, the gloss would be marred by what we callled "sea shelling". This is similar.

             

            I made small jpgs to give you an idea where these things appear: one overall shot, one detail. If these are not informative enough, I will post a link to the full image.

             

            streaks 130622.jpgShelf comp 1.jpg

            • 3. Re: Real streaks or screen artifacts?
              Trevor.Dennis CommunityMVP

              Stan, I have looked and looked and can see no problems.  Sounds like your setup - video driver perhaps?

               

              [EDIT]  What bit depth are you working in?  That's a pretty fine gradient and could well tend towards some posturization at 8 bit.  It's nice work, and I'd say you know what you are doing, and would know a wee bit of noise can hide those sort of artefacts. 

              • 4. Re: Real streaks or screen artifacts?
                Stan Patz Community Member

                Dear Dennis,

                 

                Yuh, I know it is a subtle effect. I am concerned that in half tone reproduction, the problem will get worse...or better.

                 

                Here is another image with the effect enlarged. I made a 4x5 image at 100ppi and filled it with neutral gray. Then I created a new layer, filled it with neutral gray and put it in the Overlay mode. I got a big brush loaded with black at 50% opacity and brushed across the top. Then I did the same for the bottom with white. The attached photo is an enlarged section of the boundary; it shows a lot of horizontal banding. I see this effect with many of PS tools, particularly the Gradient tool and soft-edged brushes.

                 

                OK, I think I have the answer to my own question. I am working at my office computer instead of my PS computer; I wanted to see the effect on another screen. I have the attached image nice and large with the bands very evident. I opened the Info pallet, got the Eyedropper tool and slowly worked down the image crossing bands. The RGB numbers were even and slowly worked from darker to lighter (at the top to middle of the image). When I crossed from a light band to a dark band, there were no jumps, just an even gradation.

                 

                So the Photoshop numbers are good, my screens cannot reproduce a smooth gradient; one is a Dell 2408WFP, a well reviewed monitor. Please try this exercise and tell me if you make streaks on your own system.

                streaks.jpg

                • 5. Re: Real streaks or screen artifacts?
                  PLovka

                  Stan,

                   

                  Sorry, but I can see the streaks on my monitor in two of your sample pictures.

                   

                  In the close-up pic, I see shades of dark gray and purple streaks running top to bottom. I don't see anything In the photo next to it. In your third picture, I see shades of white and grays running left to right. Is that what you see???

                   

                  I did not download the pic's and look at them in Photoshop or Lightroom. I browsed them using a Google Chrome Browser. My screen resolution is 1920x1080. Oh, I don't see streaks on my photos when using a gradient tool.

                   

                  Phil

                  • 6. Re: Real streaks or screen artifacts?
                    Stan Patz Community Member

                    Dear Phil,

                     

                    Thanks for taking the time and looking at my photos.

                     

                    My Dell 2408WFP has a native resolution of 1920x1200 and the photos were composed in 8 bit. I don't think my art director or the various printers who will handle this image would appreciate a 16 bit file. Anyhow, you do see the artifacts I am worried about, including the subtle magenta/green banding.

                     

                    Now that I am investigating the streaks with you here, I have shown to my satisfaction that the problem is in screen reproduction. Photoshop is showing smooth numbers, but my two screens are posterizing. Thanks for your help.

                    • 7. Re: Real streaks or screen artifacts?
                      Trevor.Dennis CommunityMVP

                      Stan the banding is very evident on my screen in your post #4.  Running the eye droper down it, I am seeing definitely stepping, and very subtle colour shifts.  Note I can only see those by the numbers, and not on the screen.  If I apply Gaussian blur at strength 50, I get a very smooth and even change of the numbers, with zero colour shift.  I'm using a Dell 2709W with Huey Pro.  The banding looks worse on my second monitor - A Philips 19inch 4:3 (also controlled by the Huey Pro)

                       

                      I always say that the numbers don't lie, regardless of what you think you can see.

                      • 8. Re: Real streaks or screen artifacts?
                        Stan Patz Community Member

                        I always say that the numbers don't lie, regardless of what you think you can see.

                         

                        Dear Dennis,

                         

                        I knew this "streaking" would be hard to discuss. My original image is pretty large, over 30MB without layers, but I had to squeeze it and my screen grabs, down to small jpgs, just to show you examples.The images get translated from tif to jpg, and then published on the web, and finally get viewed on all your different monitors.  With all those transfers, who knows how many other problems get "baked in"?

                         

                        Since the gradient numbers on my original are smooth and neutral (regardless of what I see), I will submit the final image to my client knowing my part of the job was finished properly.