18 Replies Latest reply on Jun 22, 2008 8:54 PM by Jim_Simon

    Blue skies turn gray.

    Jim_Simon Level 8
      I wonder if anyone can check this behavior in CS3.

      I noticed that simply applying the Magic Bullet Looks effect, without ever opening the Looks Builder and making any adjustments, that my blue skies turn gray. Viewing on a calibrated, external NTSC monitor, the original DV footage shows a very clear delineation between blue sky and white clouds. After adding the effect, I get a sort of gray mush, with no delineation between clouds and sky. My once beautiful day looks overcast and about to rain.

      Upon further investigation, I found some more possibly useful data.

      For starters, all MB effects cause this to happen - Looks, Colorista, Frames, Deartifactor, Misfire, etc. I then checked several other effects native to Premiere Pro 2.0, such as Levels, and found them to be causing the same issue when applied, even before any changes had been made with the effect. Not all effects do this, however. The Fast Color Corrector, for example, does not change the video in any way until I make a change to the effect parameters. Same with the other effects in the Color Correction folder.

      I then tried other clips with sky in them, some from the current project, some from other projects (meaning they were shot on a different day, on a different tape, so camera issues could potentially be eliminated). Some of the other sky clips exhibited the same issue, others did not.

      Eventually I took a look at my clips through Premiere's built-in scopes. I found that the clips showing a problem had IRE levels in the sky portion of the image ranging from a low of 80 to a high of 120. Applying the effects in question immediately compressed that range, making the lows about 90 and the highs about 100.

      I haven't the technical knowledge to even guess at a cause, let alone a solution, so if anyone has any thoughts, please share. I'd really like to keep my blue skies!
        • 1. Re: Blue skies turn gray.
          shooternz Level 6
          I have never observed that behaviour but will do a little test later this morning when in I go over to my edit suite.

          Which version of 'Looks' are you using. ie latest or previous
          • 2. Re: Blue skies turn gray.
            shooternz Level 6
            Did a test that confirmed to me that simply applying "Looks" (latest version) had no pre effect on a clip. Visual or via waveform monitor,

            Try applying Looks to a Bars and Tone clip as a test?

            BTW

            >clips showing a problem had IRE levels in the sky portion of the image ranging from a low of 80 to a high of 120. Applying the effects in question immediately compressed that range, making the lows about 90 and the highs about 100.

            It would seem that Looks is automatically applying a Level Limiter. It has always been good practice (and a tip from MBs) to adjust Levels before applying FX (of any sort).

            Photographically - any over exposure desaturates color towards white. Grey is partial white.
            • 3. Re: Blue skies turn gray.
              Jim_Simon Level 8
              Thanks for testing.

              Did the test clip have IRE levels over 100? I feel that's a critical factor here.

              It's also not just Looks or other MB effects, but most of the effects native to Premiere. CC effects seem to be the exception.

              I'll see what happens with bars.
              • 4. Re: Blue skies turn gray.
                shooternz Level 6
                No they didnt and hence my follow up comment regarding levels.

                Try applying Levels to the problematic clip(s) and then see what happens. (You may have to render and export them out and back begfore applying 'Looks')
                • 5. Re: Blue skies turn gray.
                  Jim_Simon Level 8
                  The Levels effect applies the same dynamic range compression even before I make any adjustments with the effect. My 80 to 120 IRE sky gets 'crushed' to 90-100.

                  That's why I think this test needs to be performed with a clip that has over 100IRE signal.
                  • 6. Re: Blue skies turn gray.
                    shooternz Level 6
                    How did you produce a clip with a level of 120?

                    What camera ?

                    Can Levels bring it down?

                    Which version of LOOKS?
                    • 7. Re: Blue skies turn gray.
                      Jim_Simon Level 8
                      The clips were produced in the normal course of shooting on my Panasonic DVC80, which is basically a DVX100 minus the 24p electronics.

                      Levels do bring it down, as well as many other effects, as soon as I add the effect and before I change any effect parameters. It's that automatic clamping down that I'm curious about.

                      Looks version 1.0.
                      • 8. Re: Blue skies turn gray.
                        Jeff Bellune Adobe Community Professional
                        There are very few filters or effects in PPro that won't automatically clamp the luminance. IIRC, ProcAmp is one of them.
                        • 9. Re: Blue skies turn gray.
                          Jim_Simon Level 8
                          Thanks Jeff.

                          Do you know why? As I said this automatic adjustment is actually smudging the blue in my skies and the white in my clouds and turning them both into a gray mush. They look fine on the timeline and out to an NTSC monitor - until I add any effects.

                          Also, I did notice the same thing happening even on bars. When viewed through through the scopes, you can see an (albeit small) change as soon as the effect is applied, even before you change any parameters.
                          • 10. Re: Blue skies turn gray.
                            Jeff Bellune Adobe Community Professional
                            I think I wrangled a long, technical explanation out of someone a long time ago. I don't remember the details, but the gist seemed to be that for most effects, a conversion to/from RGB was required, and the conversion necessitated the clamping. I got the impression the issue was non-negotiable from an engineering standpoint.

                            But my memory isn't what it used to be, so I could be completely wrong. ;)
                            • 11. Re: Blue skies turn gray.
                              shooternz Level 6
                              Makes sense that you would have to pin the RGB range at 0-255 to be able to process it within the range of RGB Effects controls.
                              • 12. Re: Blue skies turn gray.
                                Jim_Simon Level 8
                                I guess that makes sense. But I thought 100 IRE was equivalent to 235 and 120 IRE at the 255 limit.
                                • 13. Re: Blue skies turn gray.
                                  shooternz Level 6
                                  You may be right.

                                  Google is our friend
                                  • 14. Re: Blue skies turn gray.
                                    shooternz Level 6
                                    Googled:

                                    Converting between IRE and RGB values should be a simple job for the codec. White(100 IRE) is equal to RGB 255, 255, 255, and black (7.5 IRE) is converted to RGB 0, 0,0. Everything between 0 IRE and 7.5 IRE, while it is recorded by the PVR, isdiscarded when converting into RGB, since there shouldn t be anything thereanyway.
                                    • 15. Re: Blue skies turn gray.
                                      shooternz Level 6
                                      Jim

                                      Maybe of interest to you if you have Adobe On Location

                                      Checkout the RGB Levels in the Spectra Analyser using the Color Bars. This shows RGB Luma against an IRE Scale

                                      Kind of shows you where your sky should be sitting to be really blue
                                      • 16. Re: Blue skies turn gray.
                                        Jim_Simon Level 8
                                        I guess this starts to get to the heart of the matter.

                                        >"Digital video is created using an 8-bit (or sometimes 10-bit) quantization of the incoming analog image. With 8-bit digital video, the 7.5 to 100 IRE analog range is divided into 256 steps between total black (0) and total white (255). In RGB values, 0 to 255 is the full range, but according to the 601 specifications, the range for YCrCb digital video was reduced so that black = 16 and white = 235. This was done to accommodate "real world" video signals that tend to exceed both ends of the scale and to accommodate the set-up level of NTSC.

                                        >Unfortunately, not all NLEs work this way. Some take video in and digitize it based on the 0-255 range, while others use the 16-235 range. Since no video can exist below digital zero, any analog video, which is lower than 7.5 IRE or higher than 100 IRE, will be clipped in a system that scales according to the 0-255 range, since there is no headroom on such an NLE. Some NLEs that work in this RGB mode will correct for the headroom issue as part of the conversion done with the incoming and outgoing video signals."

                                        Seems like Premiere is keeping the DV as YUV until the effect is applied, where it goes to RGB. Bummer. My skies really looked a nice shade of blue.
                                        • 17. Re: Blue skies turn gray.
                                          shooternz Level 6
                                          Get a ND grad filter or some lights for the subjects(and stop down)
                                          • 18. Re: Blue skies turn gray.
                                            Jim_Simon Level 8
                                            Good idea for production shoots. A little difficult for run and gun wedding shoots. Although, setting zebras at 80% and stopping down may be an option for future shots.

                                            However, I'm a little stymied on how to keep my blue skies for this project.