37 Replies Latest reply on Dec 3, 2008 12:31 PM by Jao vdL

    Halo artifacts on cropped images

    dorin_nicolaescu Level 5
      Sometimes images cropped in ACR show strange halo artifacts around sharp edges:

      http://farm4.static.flickr.com/3152/2861862047_577ec988e6_o.png

      None of the images has been resized in ACR. The amount of sharpening and any other settings are the same. The only difference between the two is that one have been cropped in ACR, the other has not been.

      These artifacts are even visible in ACR's own preview window. They are especially easy to see around white edges against a dark gray background.

      I have a feeling that these appear only when the crop rectangle does not match the pixel boundaries and, as a result, as the pixels can only be integer, resampling is needed to 'round' the fractions of pixels to integer pixels.

      P.S. I believe this bug is related to Lightroom's resize on export algorithm ( Shao Zhang, "Lightroom 1.3 resize on export artifacts still there, samples inside" #, 16 Nov 2007 2:12 pm), as well as to upscale 'ringing' artifacts in ACR ( Olaf Ulrich, "Resizing a camera raw image" #1, 25 Jan 2008 6:22 am), mentioned by Olaf Ulrich many times on this forum but not seemed to be heard anyone else.
        • 1. Re: Halo artifacts on cropped images
          dorin_nicolaescu Level 5
          > What are the sharpening settings?

          Lightroom defaults: 25; 1; 25; 0. But It doesn't really matter. Yes, sharpening accentuates this effect, but, as I noted, both images use the same amount of sharpening - it's just that one of them is cropped.
          • 2. Re: Halo artifacts on cropped images
            Jao vdL Adobe Community Professional & MVP
            These artefacts happen at zero or default sharpening settings. As Dorin notes, the ONLY change is cropping a little. It is likely caused by the specific implementation of the lancszos resizing algorithm ACR uses that somehow kicks in even when only cropping and has been discussed over and over and over as Dorin notes. But it hasn't been fixed yet. That said, it is only an issue on the subset of images that have a sharp high-contrast edge of some kind. Say a tree's branches against a bright sky or lettering on a dark background. It is very annoying when it happens as you cannot use ACR or Lightroom to crop or scale those images without creating these ugly artefacts.
            • 3. Re: Halo artifacts on cropped images
              MadManChan2000 Adobe Employee
              Dorin, can you post a DNG raw file? (please embed the conversion settings you use)
              • 4. Re: Halo artifacts on cropped images
                dorin_nicolaescu Level 5
                > Dorin, can you post a DNG raw file? (please embed the conversion settings you use)

                There it goes... with the crop and everything embedded. https://www.yousendit.com/download/bVlCUXVzR3NwM25IRGc9PQ

                Some notes:

                1. Guys, please note that the artifacts are most obvious in the lettering. Even with zero sharpening.

                2. Remove the crop, while keeping the rest of adjustments the same - lettering is tack sharp and clean!

                3. Try upsampling in ACR - halos are back again!

                4. Try downsampling - same halos.

                5. Try exporting at original size in Lightroom - Perfect! Try exporting and resizing by as little as one pixel (either shrinking or enlarging) - halos again!

                So it all goes down to RESIZING in ACR/Lightroom. Something is wrong wit the algorithm.
                • 5. Re: Halo artifacts on cropped images
                  MadManChan2000 Adobe Employee
                  Thanks for the info. I have the file now.
                  • 6. Re: Halo artifacts on cropped images
                    01af Level 1
                    Oh dear! That's exactly the kind of ringing artifacts you'd get, and always got, from upsizing in Camera Raw. New---to me---is that they also occur when just cropping or downsizing.

                    Fortunately, the work-around is easy: simply avoid cropping or resizing in Camera Raw; do that in Photoshop instead.

                    -- Olaf
                    • 7. Re: Halo artifacts on cropped images
                      dorin_nicolaescu Level 5
                      > Fortunately, the work-around is easy: simply avoid cropping or resizing in Camera Raw; do that in Photoshop instead.

                      Unfortunately, I use Lightroom (this family of bugs also affects LR) as one big workaround for ACR/Photoshop, so this workaround is not working for me. :)
                      • 8. Re: Halo artifacts on cropped images
                        Jao vdL Adobe Community Professional & MVP
                        >New---to me---is that they also occur when just cropping or downsizing.

                        http://lagemaat.blogspot.com/2008/08/lightroom-artefacts-even-show-up-when.html

                        >simply avoid cropping or resizing in Camera Raw

                        Unfortunately, if you use Lightroom for your workflow and printing, it is really hard to avoid that as at some stage, you'll always have some cropping or scaling. If you use ACR and Photoshop, than indeed simply do not let ACR crop or scale and you'll be fine.
                        • 9. Re: Halo artifacts on cropped images
                          Tim Lookingbill Level 1
                          And what's with the pronounced stairstepping along high contrast edges at this zoom level? I get this even with ACR 3.7. I guess this is the price you pay for not having sharpening halos or very thin halos at best.

                          The ringing is a completely different issue. This is new to me.
                          • 10. Re: Halo artifacts on cropped images
                            01af Level 1
                            Oh yes, the work-around mentioned above won't work for those who are using Lightroom only ... sorry.

                            By the way, I just tried with both ACR 4.5 and ACR 4.6 Beta, and I don't see any undue artifacts when just cropping in Camera Raw. I do see them when upsizing and when downsizing in Camera Raw.

                            .
                            Tim Lookingbill wrote:
                            > The ringing is a completely different issue. This is new to me.

                            Different issue? As far as I can tell, the 'pronounced stairstepping'
                            i is
                            the ringing---just two expressions to describe the same (unwanted) phenomenon.

                            -- Olaf
                            • 11. Re: Halo artifacts on cropped images
                              dorin_nicolaescu Level 5
                              > By the way, I just tried with both ACR 4.5 and ACR 4.6 Beta

                              Have you used the test file I've uploaded via YouSendIt? You can't always see the artifacts when cropping. It depend on how exactly the crop rectangle is placed. Try my file.
                              • 12. Re: Halo artifacts on cropped images
                                MadManChan2000 Adobe Employee
                                I see them, Dorin. However, at this time I cannot give you a timetable for a potential fix.
                                • 13. Re: Halo artifacts on cropped images
                                  Tim Lookingbill Level 1
                                  Olaf,

                                  This is the pronounced stairstepping I'm referring to:

                                  http://www.flickr.com/photos/26078880@N02/2869259694/sizes/o/

                                  Now that I've been working my way through CS2 and ACR 3.7's sharpening and demosaicing algorithm for the past couple of weeks, I now see what the advantage of this haloless stairstepped texture is useful for...UPREZZING!...as noted in the image on the right.

                                  I also found a way to get rid of the "clay" like texture to high frequency textures like grass, pebbles and twigs I've been complaining about in ACR. Start out with a somewhat tonally flat looking rendering in ACR where each end of the histogram tapers off without clipping and apply Smart Sharpen and contrast sharpening using blend if to control tonal roll off along the edges.

                                  Or in other words learn how to use the damn program.
                                  • 14. Re: Halo artifacts on cropped images
                                    Ramón G Castañeda Level 4
                                    The paleolithic ACR 3.7 is for the paleontologists to discuss. ;)

                                    Even so, from the posted examples it's impossible to tell what can be attributed to manipulating a smart object, or if both examples were treated as such Wait! Is the example on the right derived from the one on the left? Now I'm confused. Never mind.
                                    • 15. Re: Halo artifacts on cropped images
                                      Tim Lookingbill Level 1
                                      Come on, Ramon.

                                      You're brighter than that.

                                      They're the same image. The one on the right is the uprezzed version as I pointed out. I didn't use "a smart object". Where are you getting that from? Now I'm confused by your reply.

                                      ACR does render pixels quite differently than other converters and I'm just finding my way to understanding the reasons behind it.

                                      CS3's ACR 4 renders pixels the same as ACR 3.7. The rendering changed with subsequent updates to 4 that turned on mandatory noise reduction which amplified this clay like texture. I tried it out in ACR 4.5 and now prefer ACR 3.7 because at least I found a way to work around this odd texture that sharpening of any kind seems to amplify.
                                      • 16. Re: Halo artifacts on cropped images
                                        Ramón G Castañeda Level 4
                                        >Where are you getting that from?

                                        Brain short circuit, possibly triggered by the "Smart" sharpening filter mentioned, I don't know. My bad.

                                        I still don't understand whether the image on the right is the result from uprezzing the one on the left, or whether "They're the same image" means they were derived from the same original.

                                        But never mind, as long as ACR 4.6 is not involved, I'm out of here.
                                        • 17. Re: Halo artifacts on cropped images
                                          Tim Lookingbill Level 1
                                          What I was driving at with that posted sample is that this haloless stairstepped edge texture, which doesn't appear in other converters, makes for better looking extreme uprez interpolation. I assumed this was the intent behind this texture by the Adobe engineers.

                                          I couldn't get this hard edge haloless appearance from any software before until I started using ACR 3.7 sharpening combined with CS2's Smart Sharpening. Photoshop 7, scanner software, other raw converter's sharpening tools couldn't render edges this way.
                                          • 18. Re: Halo artifacts on cropped images
                                            dorin_nicolaescu Level 5
                                            Tim, Ramón,

                                            this thread is going a little off-topic.
                                            • 19. Re: Halo artifacts on cropped images
                                              Ramón G Castañeda Level 4
                                              Dorin,
                                              > thread is going a little off-topic.

                                              Many, many threads do that. Topic drift is not only inevitable, but a very, very good thing.

                                              You'll see that in many of the existing threads, and you will see it in many threads in the future.

                                              Replies and responses to the replies (or vice versa :)) often raise issues that were not contemplated in the original post.

                                              Now, if you think a new issue is hijacking your thread, just identify the new topic specifically, and you yourself or anyone else can start a new thread to redirect traffic to it.
                                              • 20. Re: Halo artifacts on cropped images
                                                Ramón G Castañeda Level 4
                                                Back to Dorin's issue:

                                                The halos are visible on the example, but I can't help wondering to what extent they are caused or exacerbated by viewing them at different percentage sizes, if that is what's going on there. Seeing the full raw image would help. I'll try downloading it.
                                                • 21. Re: Halo artifacts on cropped images
                                                  Ramón G Castañeda Level 4
                                                  Done.

                                                  I can confirm what Dorin and Eric are seeing. I opened two versions of the DNG image, one being the crop and another one of the entire raw image, after making sure the default ACR settings were the default ones for both conversions, whithout ANY of the custom adjustments Dorin had applied.

                                                  Halos are seen only in the cropped image.

                                                  That's a most impressive photograph taken under conditions that would have induced complete paralysis in me, followed by a fatal heart attack. :|
                                                  • 22. Re: Halo artifacts on cropped images
                                                    Yammer Level 4
                                                    Ramón G Castañeda:
                                                    > Now, if you think a new issue is hijacking your thread, just identify the new topic specifically, and you yourself or anyone else can start a new thread to redirect traffic to it.

                                                    This statement confused me a bit. Are you saying that someone who's had their topic hijacked should start another thread for the hijackers to use?

                                                    I thought it was the job of the hijacker. Mind you, if that was likely they wouldn't be called hijackers, would they? :)

                                                    Keith "oh look, I'm a hijacker too" Nuttall
                                                    • 23. Re: Halo artifacts on cropped images
                                                      dorin_nicolaescu Level 5
                                                      OK, sometimes it's hard to show these artifacts to others. In case one could not see them in the first example, I just found another great example of a ringing artifact. Note the halos around the thin chrome frame on the limo's window.

                                                      http://farm4.static.flickr.com/3032/2870105334_6117efb779_o.png

                                                      This one clearly shows them and that, unlike normal oversharpening halos, these are offset by one pixel from the white object they are around.

                                                      I have included a third picture that has no artifacts but has been oversharpened in Photoshop, to prove that ringing artifacts are not related to oversharpening.

                                                      EDIT: Oh yeah... and here's the DNG: http://www.yousendit.com/download/bVlDRm82eFg3N0NGa1E9PQ
                                                      • 24. Re: Halo artifacts on cropped images
                                                        Jao vdL Adobe Community Professional & MVP
                                                        I am very heartened seeing this issue (and the related one that arises upon scaling) finally recognized. I and others have been pointing this out for ages now in the Lightroom forum and other places (not the least my blog) but have gained very little traction for it. When you start seeing these artefacts, you'll see them everywhere and they'll become very bothersome. The last image Dorin posted is a very typical case: white halos on the dark side of a high contrast edge.

                                                        Finally, Eric is a superb asset to Adobe and thanks to Dorin for starting this thread here.
                                                        • 25. Re: Halo artifacts on cropped images
                                                          Tim Lookingbill Level 1
                                                          Dorin,

                                                          Yeah, I hijacked this thread. Happens all the time here and in many other forums on the web. It happens to me when I start a topic. I love it. It's interesting to see where it goes. You never know what you'll learn. Don't be too sensitive on the internets. It'll gray your hair.

                                                          Besides your issue was resolved back in post #13 when Eric Chan, an Adobe programming engineer, confirmed the ringing/crop artifact and indicated no current potential fix. Great catch by the way.

                                                          Since my issue was regarding artifacts that I at first thought were artifacts by mistake, I thought I could keep this thread at the top of the list by keeping it active posting my misunderstanding about how ACR and CS2 deals with sharpening.

                                                          I guess I should have posted my issue on the Uprez thread a couple of clicks down the list since that one more relates to my issue.

                                                          Dorin, your first sample posted in your original topic was too small for me to see what you were talking about. Since others were seeing it and I wasn't, wasn't sure what you were referring to as ringing.
                                                          • 26. Re: Halo artifacts on cropped images
                                                            dorin_nicolaescu Level 5
                                                            > Yeah, I hijacked this thread.

                                                            It's OK...

                                                            > Besides your issue was resolved back in post #13 when Eric Chan, an Adobe programming engineer, confirmed the ringing/crop artifact and indicated no current potential fix. Great catch by the way.

                                                            Yeah, you're right. And that's great! :)
                                                            • 27. Re: Halo artifacts on cropped images
                                                              Ramón G Castañeda Level 4
                                                              Keith,
                                                              >someone who's had their topic hijacked should start another thread for the hijackers to use?

                                                              Not should, can. :)
                                                              • 28. Re: Halo artifacts on cropped images
                                                                01af Level 1
                                                                Tim Lookingbill wrote:
                                                                > This is the pronounced stairstepping I'm referring to: [...]

                                                                Oh, I see. You're right, that's different from the ringing artifacts Dorin and I are talking about. A stair-stepped edge is not very smooth (that's bad) but pretty sharp (that's good). At a given resolution, I guess you can't have smoothness and sharpness both at the same time.

                                                                -- Olaf
                                                                • 29. Re: Halo artifacts on cropped images
                                                                  MadManChan2000 Adobe Employee
                                                                  Jao, if you have additional raw samples that you'd like to send me that clearly demonstrate the issue, feel free to send them to me (DNG files are fine).
                                                                  • 30. Re: Halo artifacts on cropped images
                                                                    Jao vdL Adobe Community Professional & MVP
                                                                    Eric,

                                                                    I sent you an email with a link on the madmanchan email.
                                                                    • 31. Re: Halo artifacts on cropped images
                                                                      Oh dear! That's exactly the kind of ringing artifacts you'd get, and always got, from upsizing in Camera Raw. New---to me---is that they also occur when just cropping or downsizing.

                                                                      Fortunately, the work-around is easy: simply avoid cropping or resizing in Camera Raw; do that in Photoshop instead.

                                                                      -- Olaf


                                                                      Really? So now I better not crop in ACR? Recently I had changed the habit from PS to ACR. Now I gotta change back...
                                                                      • 33. Re: Halo artifacts on cropped images
                                                                        Level 1
                                                                        Got a question in regards to the artifacts. Are they on the edges only?
                                                                        • 34. Re: Halo artifacts on cropped images
                                                                          dorin_nicolaescu Level 5
                                                                          > Are they on the edges only?

                                                                          Yes. Sharp edges of bright objects.
                                                                          • 35. Re: Halo artifacts on cropped images
                                                                            dorin_nicolaescu Level 5
                                                                            The artifacts are gone in ACR 5.2!

                                                                            Eric, sooo many thanks. I believe it is this very thread that brought this issue into attention, and helped correct a bug that I've been complaining about at least since the release of LR1 back in Feb, 2007.

                                                                            Now, I can really feel the power of this forum and how important is the users' contribution to development of this software.
                                                                            • 36. Re: Halo artifacts on cropped images
                                                                              MadManChan2000 Adobe Employee
                                                                              Yes, this thread was helpful and did lead to getting the issue identified and resolved. I used your raw file, as well as many others, for testing.
                                                                              • 37. Re: Halo artifacts on cropped images
                                                                                Jao vdL Adobe Community Professional & MVP
                                                                                Thanks Eric,

                                                                                this made my day when I found out! Hoping to use it in Lightroom too soon.

                                                                                Jao