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  • Sensor pattern

    Hi,

    just messed around with some footage I downloaded and found a disturbing sensor pattern. Not only apparent when brightening up the picture too much but also visible when setting the darkest point of the image to 0 IRE.

    Click


    Left side of the image. horizontal lines and weird colors

    Here in a much too bright version to emphazise it
    Click

    Iīm afraid, in motion such a fixed pattern will be very disruptive! It was in Franks low light footage, too, but only visible if you brightened it up far too much.
    Last edited by Felix; 09-03-2012, 08:32 AM.
    BMCC - Sony HVR-Z7 - Nikon D7100

  • #2
    Who's frame is that?

    Anyway, yes, count on it. Very Underexposed areas will look like this and it can be difficult to get rid of with noise reduction. All the data that you may see in the shadows may or may not be usable because of these factors.

    Thing is, all cameras would exhibit this if you were getting the data raw. The less compressed, the more obvious it becomes. Compression cleans things like this up in cameras like the FS100 so and so forth, but given the right amount of underexposure you can see it in those too.

    GH2 Hack is much more terrible than this, or at least I think so...

    SKYPE (best way to talk to me): Camera_Kholi | twitter
    Avery and Pete: Superseeds Feature Film Trailer

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    • #3
      Possibly that's why JB's advice has been expose for shadows on the BMCC without clipping the highlights?

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      • #4
        I donīt remember were I downloaded the footage. Somewere here in BMCuser. There was also footage of a dog in it.

        Hmmm, but if Iīm shooting a low key scene (I donīt mean low light), even if I expose to the right, there would still be dark parts in the image, like in every dark scene from a movie.
        So if that means you can never have underexposed areas in your shot (like a Night Skyline) this cam might be good for evenly lit sitcoms...

        @markwilliams: Exposig for the shadows without clipping highlights to supress noise is ok, but if you have to overexpose your shadows without clipping highlights to avoid sensor pattern, then itīs not 13 stops of DR.
        BMCC - Sony HVR-Z7 - Nikon D7100

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        • #5
          There's a difference between severely or "very" underexposed areas and underexposed areas, though. Basically, if you're in a situation where you wish you had more than say 1600 ISO, the you're in trouble.

          Here's a place where I dared to rate RED MX @ 6400 ISO:



          When I get to the original, you'll see just how bad it can get when you don't have proper amounts of light etc. But, even here you can still see the sensor pattern from everything being crazy underexposed.

          I mean, the lens was a T3.1 wide open, it's night, and it's being lit by three litepanels and two tiny kino light bulbs the size of your fingers.

          If you're in this situation, and you can't tolerate the noise, you've probably chosen the wrong camera. lol

          I'll post a raw still from this.

          SKYPE (best way to talk to me): Camera_Kholi | twitter
          Avery and Pete: Superseeds Feature Film Trailer

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          • #6
            Originally posted by Felix View Post
            @markwilliams: Exposig for the shadows without clipping highlights to supress noise is ok, but if you have to overexpose your shadows without clipping highlights to avoid sensor pattern, then itīs not 13 stops of DR.
            That's not correct. You have to do similar (please note I said similar, not the exact same thing) with Alexa because most of its DR is on the top end, not the bottom. Inverse to Epic where most of its DR is on the bottom, not the top. It's still likely to be 13, just not the kind of thirteen for lowlight shooters.

            SKYPE (best way to talk to me): Camera_Kholi | twitter
            Avery and Pete: Superseeds Feature Film Trailer

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            • #7
              Originally posted by Kholi View Post
              That's not correct. You have to do similar (please note I said similar, not the exact same thing) with Alexa because most of its DR is on the top end, not the bottom. Inverse to Epic where most of its DR is on the bottom, not the top. It's still likely to be 13, just not the kind of thirteen for lowlight shooters.
              Your shot from the red was ISO 6400. What I posted was ISO 800. I didnīt brighten up anything. I even lowered the shadows so the darkest parts are at 0 IRE.

              Look, I imagine a classic indoor low key scene with beautiful practicals all over the place, fill light off course, but dark parts, too. ISO 800, no brightening in post, just grading the picture so the shadows are just about to crush.
              If that results in a visible sensor pattern...I donīt know.

              If itīs true that the latitude is all above middle grey than itīs ok. But if itīs like a, letīs say FS700, you would end up with burned out highlights all over the place because you lightened up the shadows too much.

              I have this camera on preorder so I donīt mean to talk bad about it. Just find out if there are problems with it.
              BMCC - Sony HVR-Z7 - Nikon D7100

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              • #8
                Originally posted by Felix View Post
                Your shot from the red was ISO 6400. What I posted was ISO 800. I didnīt brighten up anything. I even lowered the shadows so the darkest parts are at 0 IRE.
                ISO doesn't matter. If it's underexposed in RAW it's underexposed. The number I gave was a rating, so basically I could've easily said 800 ISO and I would be right, the entire argument would be thrown out of the window.

                Look, I imagine a classic indoor low key scene with beautiful practicals all over the place, fill light off course, but dark parts, too. ISO 800, no brightening in post, just grading the picture so the shadows are just about to crush.
                If that results in a visible sensor pattern...I donīt know.
                The ISO doesn't matter, it's just a guideline for rating and lighting ratios. And in this scenario no the sensor pattern probably wont' show up if you've rated to say 320~640 (interior) and lit accordingly. You've got JOhn Brawley's DNGs, I don't recall seeing any sensor pattern noise or hatching.

                If itīs true that the latitude is all above middle grey than itīs ok. But if itīs like a, letīs say FS700, you would end up with burned out highlights all over the place because you lightened up the shadows too much.
                I think the disconnect is what you're used to working with and what working with RAW really means from acquisition to post. It's a little hard to explain, but basically you just don't want anything to be severely underexposed. Just looking at this image that you've posted, everything looks underexposed. You'd have to know what stop it was shot at etc. to know for sure how far under it is.

                SKYPE (best way to talk to me): Camera_Kholi | twitter
                Avery and Pete: Superseeds Feature Film Trailer

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                • #9
                  I posted that as a fov test of the tokina 11-16mm lens

                  Shot in a dark prep bay at blacklist.

                  At t4

                  Http://dankanesbmcc.blogspot.com

                  Why are you trying to lift the blacks?

                  Its dark and should be dark. Should be brought down not up.

                  Let me post a corrected frame for you.
                  Dan Kanes
                  www.dankanes.com

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                  • #10
                    Thanks Dan.

                    Clearly that frame was intentionally shot like that. I don't imagine seeing any FPN if it's handled as it was meant to be.

                    SKYPE (best way to talk to me): Camera_Kholi | twitter
                    Avery and Pete: Superseeds Feature Film Trailer

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                    • #11
                      I donīt get it completely.
                      If you went back to Redcine X and rated that shot with ISO 800 the picture would be very very dark and the pattern would be gone.
                      The BMCC picture is very very dark (also rated at 800) and shows a pattern. Iīm totally fine with such a sensor behavior if I opened up the shadows or the whole brightness to much (like ISO 1600+) but it should not be there at 800. Shadows can be noisy at 800, Iīm fine with that.

                      I guess underexposed areas just have to be really crushed in post with the BMCC.

                      @DanKanes: I didnīt lift the blacks I brought them down to 0 IRE. Iīm using a log curve to start with grading and the shadows are much brighter there. Dark should be dark, thatīs correct. Without horizontal lines going through the picture.
                      Look at the WFM:
                      click

                      Maybe Iīm just a noob to make it right. I never graded log curves before and for me it just looks like (in your picture from your blog) that you threw out all shadow detail
                      Last edited by Felix; 09-03-2012, 09:36 AM.
                      BMCC - Sony HVR-Z7 - Nikon D7100

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                      • #12
                        Originally posted by Felix View Post
                        I donīt get it completely.
                        If you went back to Redcine X and rated that shot with ISO 800 the picture would be very very dark and the pattern would be gone.
                        It would be very dark, but the pattern would not be gone. It would not vanish, it would not disappear, you're only making an adjustment to the rating. It would all sill be there. But the image was rated at 6400 and lit to 6400, so 800 would not be clean at all, it would be dark and unusable.

                        The BMCC picture is very very dark (also rated at 800) and shows a pattern. Iīm totally fine with such a sensor behavior if I opened up the shadows or the whole brightness to much (like ISO 1600+) but it should not be there at 800. Shadows can be noisy at 800, Iīm fine with that.
                        Still off, though. Your ISO doesn't matter. You don't open it up in post, you open it up before it hits the sensor. Lights.

                        The noise absolutely should be there at 800 if you do not have enough light before the camera.

                        I guess underexposed areas just have to be really crushed in post with the BMCC.
                        Still off... nothing has to be crushed, it just has to be captured according to either taste or maximum range...

                        SKYPE (best way to talk to me): Camera_Kholi | twitter
                        Avery and Pete: Superseeds Feature Film Trailer

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                        • #13
                          My thoughts on this frame here:

                          http://dankanesbmcc.blogspot.com/2012/09/using-raw.html
                          Dan Kanes
                          www.dankanes.com

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                          • #14
                            One note I forgot to add...

                            Raw records in extended range - so there is actually Sub Zero IRE information recorded.

                            I am also of the opinion that raw is NOT recorded in LOG on this camera, it's linear but raw.

                            Can anyone refute that claim
                            Dan Kanes
                            www.dankanes.com

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                            • #15
                              Ok maybe I just misinterpreted the footage through the log curve!
                              I just thought it would have the right shadow brightness but obviously it must be darker.

                              @Dan: I convert the dngs to cineform RAW, which uses 12 bit log curve, definitely not linear.
                              The camera could be linear, I donīt know.
                              BMCC - Sony HVR-Z7 - Nikon D7100

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