Grading S-Log2/S-Gamut in Adobe

[sunyata]

Interesting, check out

[jcs]

Lighting is indeed very important for color quality, with sun, HMI, and incandescent being the best so far in my testing experience: continuous spectrum. At the very end of the ARRI video (around 24 minutes) he shows the full spectrum LEDs, which have a decent full spectrum (blue LED with local phosphor). The new Remote Phosphor LEDs are excellent (Area 48 etc.), over $2.5k currently. All of our film was shot in the sun except for the green screen shots which were shot with daylight high CRI CFL and high CRI Cree LEDs: here the GH4 and 5D3 do better with color vs. the A7S.

 

From their video, the ARRI LC-7C LED looked decent ($2.7K).

 

Now that I have an X-Rite Color Checker Passport, I can shoot it on location (at least when lighting isn't radically changing) and create a high-quality LUT in Resolve which can be exported as a .cube file and used in PPro- for the ultimate white and (accurate) color balance.

 

Helpful tutorial:

[jcs]

Color correction using the X-Rite Color Checker Passport:

 

Tested: http://www.mattroberts.org/MBR_Color_Corrector/ - interesting (fully automated) but not as good as Resolve 11; not real-time during playback.

 

SpeedGrade- when Dynamic-Linking from PPro- couldn't access the SG Timeline panel to access the color matrix controls. SpeedGrade would not load the A7S's MP4's directly. Since SpeedGrade doesn't appear to use a 3D LUT and instead appears to use a simple linear matrix, the quality wouldn't be as good as a non-linear (and much more complex/detailed) 3D LUT solution.

 

Resolve 11- super easy & fast (after googling how to, video in prior post). The resulting 3D LUT plays back in real-time in PPro and looks very good (add any Lumetri effect to the clip in PPro, then load the Resolve generated .cube file).

 

When running Resolve and PPro at the same time, start Resolve first, else it might complain that there's no GPU memory.

[andrgl]

Now that I have an X-Rite Color Checker Passport, I can shoot it on location (at least when lighting isn't radically changing) and create a high-quality LUT in Resolve which can be exported as a .cube file and used in PPro- for the ultimate white and (accurate) color balance.

 

I'm surprised this hasn't been more heavily mentioned. I've been using Color Match since the beta and it has already saved me days of my life this year doing menial corrections.

 

I'd love for BM to add more editing features, so I can just stay in Resolve, but I'd much rather avoid bloat.

 

And it's free! (If you don't need NR.)

[sunyata]

just came across the "DSLR slate" app with a tiny horizontal checker? no idea if you could calibrate at all off your iPad screen, maybe you could tape a horizontal macbeth chart to the top of an iPad and use the rest of the slate's functionality.

 

 

and this one is more full featured, $30: https://itunes.apple.com/us/app/movieslate-clapperboard-shot/id320315888?mt=8

 

and the iPhone CineMeter?

 

 

got pretty high marks from users on-set.. 

[jcs]

$100 may seem like a lot for a color checker, however it's not trivial creating highly accurate color patches good enough for color calibration. The color patches/chips look like clay/paint and are somewhat fragile and shouldn't be touched etc. Apparently over time the patches will change color and no longer be as useful for calibration. It's not clear if OLED displays are accurate enough for color patches- this would probably only be useful for camera matching vs. a purely reflective surface useful for calibrating light and color on location. A purely sensor-based color calibration system which never 'wears out' would be ideal, especially if built into a camera system! (along with a depth sensor for highly accurate autofocus as well as manual focus (this tech exists right now and is very low cost)).

 

My initial tests with the A7S and the color checker were very good. After more testing I'll know if using this technique will render Canon's excellent color science advantage moot (other than out-of-the camera convenience). Especially when we can shoot a photo with the 5D3 and color checker and use that as a "match-to" reference for the A7S, FS700, GH4, etc. This technique would also work with the ARRI Alexa.

[sunyata]

yep, it's all true, but maybe instead of making a 3D LUT in resolve for use in premiere, with that auto macbeth tool (for each lighting scenario?), it might be faster to use an x-rite 3 tone grayscale checker (or use the ones on the passport) and then the eye dropper on a 3-way color corrector directly in premiere to set wb calibration. it should be fast, fairly accurate, and then you can make your adjustments. or you could just leave it all for resolve and use the macbeth tool after you do your edits, just export an XML file from premiere.

 

[Guest Ebrahim Saadawi]

 

 

My initial tests with the A7S and the color checker were very good. After more testing I'll know if using this technique will render Canon's excellent color science advantage moot (other than out-of-the camera convenience). Especially when we can shoot a photo with the 5D3 and color checker and use that as a "match-to" reference for the A7S, FS700, GH4, etc. This technique would also work with the ARRI Alexa.

Please keep us updated on matching the A7s to the 5D mk III colour science. Preferably in a separate topic for it be seen as it's an incredibly important matter and would save many cameras. 

[jcs]

sunyata- setting white balance (1 linear transform) and/or using the 3-way color corrector will perform at most 3 linear transforms: white balance for shadows, midtones, and highlights. The Resolve color-calibration method uses 20 color patches- a much more accurate non-linear transform in a 3D LUT, which is very helpful for skintones as well as preserving other scene colors correctly.

 

Ebrahim- without even testing it (yet), I'm confident 3D LUT color matching will work with the 5D3/Canon and any other camera, where both cameras shoot the same color chart in the same lighting conditions. The resulting 3D LUT can then be applied to all of the non-Canon clips and look very similar to native Canon footage. What isn't known is if a more generalized 3D LUT can be created that can color-transform (for example) Sony A7S into 5D3 color without having to shoot color charts for both cameras for every scene. For a given WB, ISO, and exposure, it might be possible (otherwise color behavior may change with WB/ISO/exposure). I'll post in a new thread when I have time to test this theory.

[mojo43]

This is very interesting. Can't wait to see the results!

[sunyata]

sunyata- setting white balance (1 linear transform) and/or using the 3-way color corrector will perform at most 3 linear transforms: white balance for shadows, midtones, and highlights. The Resolve color-calibration method uses 20 color patches- a much more accurate non-linear transform in a 3D LUT, which is very helpful for skintones as well as preserving other scene colors correctly.

 

remember the shirt was still blue in their resolve color checker tool example? at that point you have to make manual adjustments. but yes, the 3-way color tool would perform precisely 3 wb transforms (for each channel), blended based on the low, mid and high points (this was just a premiere alternative). i rarely strive for automated perfection in color correction. you get within a baseline from which you can make manual adjustments. that's why it's an art and a science. but why do the final color in premiere using exported LUTs and not just do a roundtrip to resolve?

 

I'm confident 3D LUT color matching will work with the 5D3/Canon and any other camera, where both cameras shoot the same color chart in the same lighting conditions.

 

i think the variation in environments and the different camera's color response to each scene will be the main problem with creating a Canon 3D LUT (or any camera) for an A7s, with this accuracy you desire. seems like you would need references from both cameras for nearly every lighting scenario (as you speculated) and internal camera setting would also need to be somehow on parity. even within that context, your distribution of colors could still be very different based on the camera's internal characteristics, creating tone imbalances when doing an automated color checker profile match (the blue shirt scenario) or enhancing the quality limitations of the A7s' 8bit 4:2:0 format. you could spend a lot of time trying to automate something to find that your eye is still the fastest and best tool.

[jcs]

Regarding the shirt being blue: the shirt is lavender under the tungsten light, which naturally has more red light (warmer). In order to compare colors between the shots, he needed to run the color match on the tungsten clip, which he did not do. He trusted his naked eye comparing un-corrected tungsten light against corrected fluorescent, which is not accurate.

 

While our eyes and brain are good at detecting 'healthy' color for skintones, charts and scopes are needed to ensure accurate color- for a variety of reasons, our eyes are not very accurate, especially if one stares at an image for a long time without looking away. This color chart matching method is currently the most accurate possible. For more accuracy we could use more color chips- 64, 100, etc., the more the better.

[sunyata]

he seemed to think the tungsten looked true to reality, i guess there is no way to know if it was adding too much red unless you see the shirt for yourself. you're correct though, he didn't test it. anyway, i'd also like to see your test, good luck. 

 

While our eyes and brain are good at detecting 'healthy' color for skintones, charts and scopes are needed to ensure accurate color- for a variety of reasons...

 

it's very true in photography and pre-press, or calibrating monitors. in post production (depending on what you're doing), while it helps of course to have good* footage, most of the work in flame (for example) is very creative and often subjective. clients generally have a low level of interest in spot on color. if it doesn't look right to someone, good luck arguing that the color is accurate based on a color checker. 

 

for one scene in american horror story, the dp shot 16mm film, overdeveloped it 2 stops, then transfered to u-matic tape and back to a 2k digital master, all to re-create the look of a 1980's television documentary.

 

*for the look you need to achieve.