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Getting Pocket 4k to (mostly) match Arri Log C Rec 709

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  • Getting Pocket 4k to (mostly) match Arri Log C Rec 709

    Hey gang,
    So I've been working on making the Pocket 4K work as an easy and simple to use (especially in post color grading) B-Cam to the Alexa. Having owned and shot on an Alexa for the last couple of years I have come to love how reliable and straightforward grading the Alexa footage is. Shoot it in Log C, toss the Arri Log C to Rec 709 LUT and then sweeten the grade to taste/style. Because of how watertight the Log C to Rec 709 workflow is on Alexa footage most of my grades for the Alexa aren't terribly deep. I don't need to jump through hoops just to get a balanced, normal, pleasing neutral starting point. Now if I'm going for a *very* specific look or style of course the nodes pile up, but all of that is downstream of a rock solid, easy neutral grade I get with the Alexa. So I wanted that same simple workflow with my new Pocket 4k. I like how flexible BRAW is, but the default factory look of the Pocket 4k is a bit punchier than the Alexa. The Pocket 4k's default look is not ugly by any stretch, but it's certainly distinct, which makes it hard to mix the two in the same edit. So I've cooked up a LUT that gets me most of the way there. It's not perfect, but I think the results pass the "squint test", which is good enough to intercut the footage without any major bumps. Let's have a look from the top...

    The footage straight out of each camera, plus a white balance and exposure adjustment. Same lens (Zeiss ZF.2 50mm cinevised). Pocket 4k using a Speedbooster while the Alexa is equipped with an aftermarket Nikon lens mount.
    The difference in sensor sizes, gamut outputs, and Speedbooster influence pretty much precludes a *perfect* exposure match in camera. So the goal was to get close enough, which we could do quite easily. The lighting set up for this test lies comfortably within the dynamic range of the Alexa, while it's probably pushing the outer limits of the Pocket 4k.
    The Pocket 4K footage has noticeable magenta cast out of the camera, where the Alexa has its signature green cast. As noted above, both of these clips have had their tint corrected. Overall the Pocket 4k Film log is contrastier and more saturated than Arri Log C.





    Applying the "usual" color space & gamut LUT to each footage to get them into Rec709 gamut/color space. The Pocket 4k is using the built in "BlackMagic Pocket 4k Film to Extended Video 4" LUT that comes with DaVinci Resolve. The Alexa using the industry standard "Arri LogC to Rec709" LUT.
    Pocket footage looks nice in its own way, but it doesn't cut well with Alexa footage. Some quick exposure, contrast, and saturation adjustments would help, but the way the two cameras handle color would still be fundamentally problematic.






    If we take it one step further and add the same Rec709 based Film Convert look FX to each of the Rec709 corrected clips, we see the Pocket 4k footage and Alexa footage get a little closer in vibe, but the original issues in the color space correcting BM LUT work are still present, as they always would be. It's axiomatic in color grading that issues earlier in the node stream still exist downstream.
    At this stage throwing a look FX or LUT onto it isn't going to fix the fundamental differences in the camera's footage.






    So here we see what it looks like using my own custom LUT to make the Pocket 4k footage look more like Alexa footage that has the Arri LogC to Rec709 LUT applied.
    And no, it's not a *perfect* match. To get an absolutely perfect match requires a level of experience and skill which sadly outstrips my own at the moment.
    But my goal is to get *close enough* that I can treat both cameras pretty much the same in my grading work flow.
    In that respect, I think I've found some measure of success.
    There are still differences, so in some scenes I will likely employ some minor tweaks down stream to adjust where the LUT cannot 100% accurately hit the mark. But we're talking a single node here or there to tweak, not an entire new parallel tree. As a time saving device I think the custom LUT does the job.







    Just for giggles I threw a Rec709 based Film Convert FX node onto both clips. Again, not perfect, but the typical audience member could watch these cameras intercut and not get bumped out of the experience.






    So at this point I am comfortable shooting on both the Blackmagic Pocket 4k and Arri Alexa on the same project and in a couple of quick nodes get them looking *pretty much* the same. In the quick turn around world of indy film or second tier commercial post-production I'm thinking this is a win.

    And if budget or physical constraints keep me from shooting with the Arri Alexa, this LUT allows me to use my Pocket 4k as the primary camera while still getting a look that is, while not perfect, a workably close approximation of the Alexa (minus whatever physical restraints the BMPCC4k sensor introduces). It's silly to promise that a Pocket 4k can deliver 100% of what the Alexa can and I'm not delusional enough to attempt to, but I was pleasantly surprised that I could get this close. BM really do have themselves a robust little camera with the Pocket 4k.

  • #2
    Nice!
    Very helpful.
    Cameras: Blackmagic Cinema Camera, Blackmagic Pocket Camera (x2), Panasonic GH2 (x2), Sony RX100 ii, Canon 6D, Canon T2i,
    Mics: Sennheiser, AKG, Shure, Sanken, Audio-Technica, Audix
    Lights: Every Chinese clone you can imagine

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    • #3
      What's the workflow like?

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      • #4
        Originally posted by EYu View Post
        What's the workflow like?
        Footage in.
        Adjust tint, WB, and exposure using RAW panel.
        Drop the LUT onto the first node in the tree to get your Alexa like neutral Rec709.
        Grade to taste from there.

        edit: By way of comparison, the node tree I used to make the LUT had 54 distinct operations/nodes. So, one node vs 54 is the time savings I wanted.
        Last edited by keithlango; 08-07-2019, 08:30 PM.

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        • #5
          @keithlango
          Looks promising. Sooo... do you have intentions to share the LUT? =)

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          • #6
            Can you share or sell the lut? If not, I'm not sure how this helps us beyond knowing what we are missing out on!

            Too bad BlackMagic cannot supply such transformations to us.

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            • #7
              Yeah, sorry. I realized that I was unintentionally obtuse about that. My bad.

              Indeed I will either share it or sell it for a very friendly price. I haven't sorted that part out yet as I've not checked the market for what people would pay for a LUT. I'd be open to pricing suggestions.

              Right now I'm working thru the kinks with it. The way the two cameras handle blue in their color science is very different, and that's the one thing I'd like to have a better handle on before putting it out to the public. To my eye I actually like the way the BMPCC 4k handles blue better than the Alexa, but the point of this LUT isn't to bake in my preferences but to get us close to the Arri look. I'm also still tweaking the greens. I'm close but still not there yet. Again, I won't ever promise a pure 1:1 match, but I do want to get as close as I can before asking people to part with money, even if it's just a little bit.

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              • #8
                Originally posted by keithlango View Post
                Yeah, sorry. I realized that I was unintentionally obtuse about that. My bad.

                Indeed I will either share it or sell it for a very friendly price. I haven't sorted that part out yet as I've not checked the market for what people would pay for a LUT. I'd be open to pricing suggestions.

                Right now I'm working thru the kinks with it. The way the two cameras handle blue in their color science is very different, and that's the one thing I'd like to have a better handle on before putting it out to the public. To my eye I actually like the way the BMPCC 4k handles blue better than the Alexa, but the point of this LUT isn't to bake in my preferences but to get us close to the Arri look. I'm also still tweaking the greens. I'm close but still not there yet. Again, I won't ever promise a pure 1:1 match, but I do want to get as close as I can before asking people to part with money, even if it's just a little bit.
                Can't ask for anything more.
                Cameras: Blackmagic Cinema Camera, Blackmagic Pocket Camera (x2), Panasonic GH2 (x2), Sony RX100 ii, Canon 6D, Canon T2i,
                Mics: Sennheiser, AKG, Shure, Sanken, Audio-Technica, Audix
                Lights: Every Chinese clone you can imagine

                Comment


                • #9
                  Have you considered an ACES workflow?

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                  • #10
                    Originally posted by keithlango View Post
                    By way of comparison, the node tree I used to make the LUT had 54 distinct operations/nodes. So, one node vs 54 is the time savings I wanted.
                    No reason why a shot on sticks with constant lighting of a well-lit subject should have 54 nodes or operations. Something's not adding up here.

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                    • #11
                      Originally posted by keithlango View Post
                      Footage in.
                      Adjust tint, WB, and exposure using RAW panel.
                      Drop the LUT onto the first node in the tree to get your Alexa like neutral Rec709.
                      Grade to taste from there.

                      edit: By way of comparison, the node tree I used to make the LUT had 54 distinct operations/nodes. So, one node vs 54 is the time savings I wanted.
                      So grade to taste comes after the LUT and not before? Isn't that contrary to the common workflow where the LUT goes last and adjustment happens before the LUT node?

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                      • #12
                        Originally posted by Jim Simon View Post
                        Have you considered an ACES workflow?
                        Yeah, like this. I just moved from RCM to ACES workflow and be great if there's any consideration for ACES.

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                        • #13
                          Originally posted by EYu View Post
                          Yeah, like this. I just moved from RCM to ACES workflow and be great if there's any consideration for ACES.
                          Yeah, I've used ACES before for mixing RED footage with other cameras. It was OK, but klunky and even then it didn't really deliver on the promise (for me, at least). The sales pitch with ACEs is as long as you have your IDT's set right the footage should look the same. Ehhh.. kinda, but not really. I will admit that I've not used it much since then and I didn't bother with it when I got the pocket 4k. I'm kind of a grumpy old man when it comes to software. If it lets me down in 2001, and I find my own work around then I'll keep using that work around even if they fix the software in subsequent years. I have Maya scripts I wrote to get around bugs and feature failures that are going on 20 years old. Have they fixed the problem? Sure, like 10 years after I had my own solution. So I keep using mine because it till works. I'm an odd duck, sure.

                          In writing this response I thought I should at least take a look at ACES so as t not be a total obstinate ass. hah. After messing with Pocket 4k and Alexa footage in an ACES workflow I'd say it does a nice job, but the tone curve is still a bit contrasty in the bottom end- something I had to fix in my stuff as well. Greens need work and it has the same troubles matching the blues that I am having, so that offers some odd form of comfort to me. hah. All that to say- ACES isn't magically solving my problems for me in a fashion that's any less hacky than my LUT path. But I'm not an ACES expert. I'm a VFX/CG/Digital media generalist.

                          That being said there's lots of ways to cook a fish. If you like ACES, awesome!

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                          • #14
                            Originally posted by GeranSimpson View Post
                            No reason why a shot on sticks with constant lighting of a well-lit subject should have 54 nodes or operations. Something's not adding up here.
                            Yeah, I was kinda surprised it has taken that much myself. What I'm doing is taking a shot of an X-Rite chart and swatch by swatch correcting the match up problems I'm seeing. Lots of Hue vs hue, Hue vs Sat, Sat vs Sat, Hue vs Lum, color masks, custom curves for tone remapping, etc. etc. And each swatch needs at least one of these operations, if not a few in concert. I keep each op in a separate node so I can turn it on/off to judge its impact and dial it in. It's tedious but it offers really fine and specific control. I'm not experienced enough to know a better way, tbh.

                            So please don't take this as being salty because I'm not. Sincerely- if you have a way of doing it more efficiently while still addressing all the minor and highly specific challenges I'm seeing in getting a match then I am all ears.

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                            • #15
                              As someone that uses UMP and P4k alongside each other routinely....

                              You need an exposure ramp to clipping in there :-)

                              The DR differences then starts to become more apparent, which isn’t something you can grade out.

                              And I’ve seen Coloourist have many nodes on a grade. It’s a common technique to copy all the “tools”, various qaulifiers to tweak, set to off but faster to apply if you want to do that.

                              One colourist I worked with a fair bit only ever seemed to use one node and did everything off the desk. He was so fast I could barely finish asking for what I wanted and it was done.

                              This guy seemed to only ever use one node most of the time.

                              https://www.instagram.com/p/BahYeRjF...d=1he0esk07r5v

                              JB

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