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GH5 to Alexa Conversion


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Sure; it depends on what you'd like. Fuji and BMD have very good, usable color. I personally will use P4K with GH5; I hope to have EC to do a production this summer. 8 bit is tricky; I'd prefer t

"GH5 V-Log and Hybid Log-Gamma are transformed to precisely match the color science of the Alexa, without compromise." "The GH Alex conversion completely transforms the GH5 image, addressing ever

Emotive Color Version 3 Core LogC Details - Rewrote engine to work at 65x65x65, main files are now at eight times resolution (supporting files processed at that resolution) - Fine tuned mu

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1 hour ago, AaronChicago said:

So I've been doing a ton of testing with VLog L and various conversions, techniques, profiles, etc. I ended up doing a head to head test with the Alexa Soft (Daylight) Rec 709 vs VLogL to V709_100 (Panasonic's default VLog conversion)

That checks out;

AV.gif

When closely matching contrast and saturation between the two, the brighter greens,  darker blues, and smoother skin tone from shadow to light really stand out here.

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They are different for sure, but that is with no secondary adjustments. I naturally would bring down the sat of green and shift the hue. Skin tone could use a slight shift of green hue. This isn't a knock at all on your Alexa LUT b/c I love it. More of a compliment to the Varicam LUT which I threw in the trash last year after getting weird macroblocking with the GH4.

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  • 2 weeks later...
On 30/11/2017 at 8:50 PM, Sage said:

"GH5 V-Log and Hybid Log-Gamma are transformed to precisely match the color science of the Alexa, without compromise."

Sage, what's your take on the GH5s' colour science, how much it differs from the GH5? Are you planning to do an Alexa-matched profile for that too?

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6 hours ago, Juan Melara said:

This is actually really impressive. Top work!

How does the GH5 footage feel to grade once converted? I presume it wouldn't handle quite as nice as actual Alexa footage?

Thanks Juan; grading the Alexa seems especially silky to me. Perhaps its the ProRes I frame, the diffused 2k, uniformity of the bits, psychology, or some combination of the lot. The conversion is largely smooth and uniform, as a continuous transform of the space. The GH5 has quite a bit more detail than my Alexa C

4 hours ago, Liszon said:

Sage, what's your take on the GH5s' colour science, how much it differs from the GH5? Are you planning to do an Alexa-matched profile for that too?

From what I can tell, it seems very similar, perhaps with a less green red. There are also the new clipping fixes like in GHa, though the rolloff remains sudden. GH5S support is the plan; Colby Moore will be sending me his GH5S to do the conversion with once I am done primary work on the new process

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@Sage Am I right in understanding that your lut converts GH5 VGamut to Alexa Wide gamut? If so, the "correct" way to use your luts would be to use GHa LogC with an Alexa Wide Gamut to Alexa X-2 conversion. When I do this, colours look more correct - not too saturated and skintones are not too magenta.

Here's a comparison with actual X-Rite colorchecker values from BabelColor in the centre as a reference. I've added a curve to each to match to the chart's gamma.

(VLog to GHa LogC) + (LogC Gamma & Alexa Wide Gamut to Alexa-X-2 Gamma & Alexa-X-2 Gamut) BEST MATCH

5a885d05b0cbd_01GHaLogCtoAlexagammagamut.jpg.3b9063a8dceb0fbf75451bc8a96968e0.jpg

 

(VLog to GHa Main) - too saturated

5a885d06e95c4_02GHaMain.jpg.abbecfa1d8f63708e75d3d772693683f.jpg

 

(VLog to Varicam V709) - better, but not as good as the first one

5a885d0823785_03PanasonicV709.jpg.f1676992e9fecb1649452cb50723251f.jpg

 

So as far as I can see, the colours that GHa gives should (technically) be transformed by using them with a LUT that expects Alexa Wide Gamut. So I'm curious as to what you see is the role of GHa Main and Soft? I understand your reasoning for the curves you chose for each, but what about the colour?

 

 

 

 

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That's right, the result of using GHa LogC is a stand in for Alexa LogC. Going from there, it may be treated as LogC from an Alexa (it can accept Arri's Rec 709 or other transforms intended for LogC). GHa Main and Soft are alternatives to Arri's Rec709; they all handle saturation in a way that is reminiscent of film (and is not in Alexa LogC natively), but place overall saturation and contrast differently as a grade base:

Main - Most Saturation, Middle Contrast (Mostly linear)

Soft - Middle Saturation, Lowest Contrast (Mostly linear)

Arri's Rec709 - Least Saturation, Most Contrast (S-emphasized)

 

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But Main and Soft don't perform the transformation from Alexa Wide Gamut to Rec709 primaries. So the hues are "wrong" - the are the colours of an acquisition colour space.

GHa LogC to Alexa X 2 gamut gives colour as Arri intended, I'm thinking. But Main and Soft are simply slightly more contrasty and more saturated versions of Log C (with saturation roll-off?).

Now, this might be of interest as a look in itself, especially if people are grading Arri LogC directly and leaving the colour space untouched. But I would suggest to you that if Main and Soft are your interpretation of a film-like Rec709 look with saturation roll off and other good things, then you should transform the primaries. The ColorChecker shots above demonstrate just how far out Main is. The hue, saturation and value of colours are significantly skewed as they haven't been transformed to Rec709 primaries.

So am I right in saying that if I want to match Alexa colour, GHa LogC plus a LogC to Alexa X 2 gamut lut is the way to go?

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32 minutes ago, hyalinejim said:

So am I right in saying that if I want to match Alexa colour, GHa LogC plus a LogC to Alexa X 2 gamut lut is the way to go?

Yes, that will work well. Per that project I messaged you about, there will be a solid reference match (core focus)

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Hi @Sage, having quite some fun here tinkering with the LUTs. A question tho : In the documentation you recommend exposing VLog middle gray at a higher IRE than the Alexa. I usually ETTR, but do you have any exposing tips for HLG converted to LogC (middle gray, clean mids, shadow threshold)?

@hyalinejim : thanks a lot for those tests! Out of curiosity, have you tried to apply a color space transform from Arri ... to let's say Rec.709 on the Main LUT yet? I don't have Arri reference material to try it out :)

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3 hours ago, seku said:

 

@hyalinejimhave you tried to apply a color space transform from Arri ... to let's say Rec.709 on the Main LUT yet? I don't have Arri reference material to try it out :)

I just tried it now. The results are not so good. Adding the Arri colour space transform to GHa Main pushes a lot of the reds into negative clipping. This is especially noticeable in dark and deeply saturated reds, blues and purples. Lowering the saturation of GHa Main by a lot prevents this clipping. However, the issue is still evident (although not to the same extent) in GHa LogC. This means you might see some unnatural colours when using GHa LogC with LUTs that expect an Arri input. I would not use Soft or Main with Arri Luts at all.

VLog - chart exposed for middle grey

5a8b7d8d7da2a_01VLog.thumb.jpg.bc88bc8f4a76c3f1c7ed8b8d75addea1.jpg

 

Add GHa Daylight Main

5a8b7d8bbdb9e_02GHa.thumb.jpg.4e4606995552c6c2865a33daf93dc319.jpg

 

Add Arri LogC to X 2 gamut only

5a8b7d8a1138d_03GHa.thumb.jpg.f7fdb340d1123047d1761bd604e3e088.jpg

 

If you look at the bottom of the waveform you can clearly see the red channel going AWOL in this step from GHa LogC to the Arri X 2 gamut (this chart shot was ETTR, and has no clipping)

GHa LogC:

5a8b802005c91_04LogC.thumb.jpg.470e0d4d6b8ee4c976948cdc3bc57084.jpg

 

Now add transform to Arri gamut:

5a8b801e5a01b_05LogCtoArri.thumb.jpg.c5414467aa68da2456362999eada1636.jpg

 

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@Sage, so I've been doing a few experiments with my GH5 footage on your LUT. 

What I love most about it is the very smooth highlight rolloff you created. It really makes the footage from my GH5 look like it's come from a much more expensive camera! 

The only real issue I've come across is that sometimes my footage appears to go too red, especially in the shadows. Skin can sometimes look very pink. I can dial this out quite quickly with curves, but do you know what the problem could be? Any user errors of such that you've found are common? (yes, I'm choosing the daylight LUT for daylight white balance etc!)

If I want to stylise the footage,  I've found that it's best to do my own grade (using Chromatic plugin on FCP) but put the look BEFORE the GHa Main LUT in the effects browser. I find it better than using LogC and an Arri LUT. 

On a personal side note, as I get better at grading - I've found that I use "film look LUTS" much less often, as many LUTs create many undesired artefacts and weirdness. With your GHa conversion, there's a voodoo which I really enjoy with it, so I see myself using it exclusively from now on.

Thank you! 

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