T.Stops Blog

The 3 Strip process color work flow : Building a color workflow for GFX100 II

Welcome back to Tstops Blog.

In this installment, I want to talk about a color process that I have been experimenting with for the Fujifilm GFX100 II.  Since last year when I used it to test My Favorite Lenses, I have fallen in love with the medium format look and Fujifilm color science for cinematic story telling.

This project for Taylor John Williams‘ song Naked, directed by Bhavani Lee, was the genesis of this color workflow exploration.  After discussing the look of the project with Bhavani, I said: ” I want it to look like the audience is looking through a window at real life”.  The idea is to create a look with rich colors and softer contrast, but will still reach white point and black point , from which I can start grading the image.  REALLIFE_11 is the look I came up with. It’s not designed to create the final look, it is designed to be the starting point.  That said, it does have a distinct look, that when dialed in, can make for some interesting results.  In the body of this post is a download link for the power grade in resolve. I encourage you to give it a try. I built this for GFX100 II, but it works on every image. The core benefits are rich skin tones and subtle color contrast that seemingly gets lost with other methods.

BTS photos by : Jesse Dvorak

 

I loaded the LUT into the Small HD monitor so I could review the look in real time.
Our Director Bhavani Lee
Bhavani Reviewing the footage with the look applied.
Filming the Broll with model Debora Comba

My first challenge when exploring any new camera is, what do I want this camera to look like?  I like to shoot my cameras with one look.  A look that I will know inside out.  Somewhat neutral and usually derived from a film emulation of some kind.  From there I can bend the look around on set with light, lenses and filters.  This gives me a consistent place to expose from and make sure the colorist has a thick negative to work with.  The LUT I use is usually passed along to the colorist to ensure they know what the intention is.

Fujifilm has built into the GFX100II ( and the rest of their line up) the very beautiful Film Sims for still images or video.  Though, in video its recorded as a baked in Rec709 look.  The Film Sims are looks that match their own classic film stocks of the past.  Eterna, Reala, Astia, Provia and more.  They look beautiful in camera.  You would think that the different film simulations were readily available as post LUTs.  They aren’t, and for a very specific reason.  Film Sims are not just a LUT the camera applies.  It’s much more than just a LUT.  It’s a constantly flexing set of mathematic rules.  It also has to bend the look to be ready for the specific light response at different ISO values, white balance  and special color options in the menus.   You can choose to enable Chrome Effects Blue, and Color Chrome.  These effects change the way certain colors render to mimic the “printed” photo look.

It is much more limiting to just apply a fixed LUT to footage after the fact and expect it to look as good as the in camera color pipeline thats dedicated to creating the look in real time.  Fujifilm has released a small handful of FUJIFILM Eterna LUTs for the GFX100 II’s specific sensor and light response.  The Eterna LUT is a little too contrasty and desaturated overall for my taste.  It’s not my favorite look to shoot with.  I never feel like it nails the color response the way I want.  One of the challenges of working with a newer camera system, especially a system that is relatively new to advanced video capabilities (GFX line specifically), is that there is little post support for the specific color pipeline and capabilities of a new sensor.  There are some LUT packs, and FilmConvert supports the FUJIFILM XH2S, but it’s sensor responds to light differently than the GFX.  While the XH2S specific LUTs sort of work, its not quite right.

Eterna LUT
My 3 Strip Process : “REALLIFE_11”

I figured, why not start from scratch.  It begged the question, what do I need? I do find the idea of a look that flexes to the needs of the shot itself like the built in Film Sim, interesting.  The main goal was to make something filmic and flexible. I wanted to build a power grade basic structure that I could drop on footage, as if it were a LUT in post, but that would give me the ability to reach a nice starting point to begin grading in a more advanced way.  I mean things like power windows, masks, color curves etc.  During this process, I realized that in order for this to work properly, it was necessary to also build an on set LUT that would feed this power grade with the color “nutrients” it needs via a dense negative.

 

Eterna LUT on Flog2
REALLIFE_11 : No grade, just the color process applied to LOG, vs the Eterna LUT in the previous example.

I had seen over the years, some experiments with a 3 Strip process emulation in resolve, similar in function to how Technicolor film worked.  It works by breaking the RGB image channels up into their individual components, and remixing them manually.  I started experimenting with this idea by building it myself from a blank slate.  This way I would understand the “why” of how it works a bit better.  I consulted many people on how it may function and what pitfalls to watch out for.  Tim Kang, DP and color science expert has had my back on this project for a couple of months now.  Every time I build a version (52 versions to be exact) I would find some new bug in the process.  Tim helped me immensely with designing a node structure in Resolve, and explained the how and why the color structure works.  The following example is from a different project that I had to regrade, simply because it was so much easier, faster, and better looking to apply the 3 Strip look.  The key difference in this example is that what I struggled with in the initial shot was getting the skin tone to look right.  The green of the glass in the window was always there and over powering.  Correcting out the green made the skin magenta, and even using the qualifier, bringing the skin back to neutral was more difficult.  Using the 3 Strip process, instead of desaturating the green away, I was able to embrace it a bit more. The skin tones were able to show through the glass, blended with the green, but still present.  The green and teal colors of the train became more vibrant, but also became more individually separated and looked truer to real life.   The image looks less muddy and cold.

FilmConvert Kodak Emulation for XH2S adjusted for GFX100
REALLIFE_11 with the 3 Strip Process.  The green tint of the glass, while present, doesnt over power the skin tone behind it. You can now see both, and it looks more natural and to my eye realistic.

 

Download the .DRX and 33×33 & 65×65 versions of the onset LUT below.   The LUT’s are made using the complete process and are designed to shoot on set with the GFX100 II in Flog2.  You can load it into your monitor with the 33×33 version, or use the 65×65 version in Resolve to make dailies.  Pay close attention to the node by node effects.  The REALWORLD_11 .DRX file is designed to give a colorful but natural image to GFX100 II Flog2 footage.  Drag and drop the .DRX file into your stills gallery in Resolve.   You have to tailor it to the scene and once its dialed in, you can save it as a separate still/power grade to then apply it to the rest of the footage in your scene.  I recommend using the stills/power grade method instead of applying the LUT, as it keeps the mechanics of the look accessible, and easy to adjust.  The saturation and contrast may not be to your liking, but thats up to you to dial it to where you like it.  It works best if you expose to the LUT provided, then apply the .DRX for full control.  Keep reading to learn what the nodes do to the image.  If you want to experiment with footage from other cameras, just reset the TINT, SAT, and Contrast nodes, then start from scratch.

DOWNLOAD HERE:  REALL IFE_11  .DRX + LUTS


PART 1: How it Works:

 

The basic set up is a series of nodes, in a specific order.  The initial input is the un-manipulated shot, and I label that TINT.  Then from there, there will be three parallel nodes, Red, Green, Blue which then come back together with a combiner node.  After the combiner node, is the Saturation Node, then Contrast node and finally the Skin node.  I separated all of these functions so that its easy to find where something is being effected, and you can always reset that node alone, and start over.

1: Tint:  This node is where you adjust your white balance.  It’s labeled Tint specifically, because the more balanced the image is before it splits up, the better time you’re going to have. The process is more sensitive to green/magenta biases.  Try to nail your WB in camera as best you can, especially in a camera like GFX100 II thats recording ProRes as the digital negative.  This means, if you want a warm look, white balance to a cooler Kelvin, or vice versa. or if you want neutral, nail it with a white card on set.

2: RGB: This series of three parallel nodes are where the magic happens.   Its a bit different than using the RGB Offset dials.   It seems on the surface that its the same thing, but the 3 strip works slightly differently in the way it blends the colors.  It is something you feel in the image and I cant quite explain, because I don’t really know what Resolve is doing under the hood.  It’s important to make sure the “Monochrome” box and “Preserve Luminance” boxes are checked. Otherwise it doesn’t work.  The Power grade .DRX file is already formatted, but if you need to go back to reset either color channel node for any reason, this is the way it should look per channel.   The levels of the red, green, and blue, are not fixed, they can be whatever value you want blended together to get your desired effect.

 

So here is whats interesting and why this is different than using the RGB offset dials.  The “tinted” monochrome images, it seems are blended together in an additive color sense.  Cranking up Red, doesn’t necessarily make the image substantially redder and neither does reducing the blue channel make it yellow.  The red channel behaves as a saturation saturation dial for skin tones and reds.  The green channel acts as a slight green/magenta bias but only in the green and yellow parts of the image and the blue channel acts something like overall saturation, with a bias towards blue.   I know it sounds confusing, but when you start using it you will get it.  This is also why its important to nail the white balance BEFORE the split.  Anything thats off, will become exaggerated.  If you feel your image keeps turning green no matter what you do, go back to the TINT node and push the tint slider a few points towards magenta.  If the image is to warm, or you can’t quite dial out some cool shadows with the blue channel, go back to TINT node and gently adjust the color temperature.   The RGB 3 Strip sliders operate slightly backwards from what seems intuitive at first, drastically increasing the output from one color channel seems to push the image in the opposite direction on the color wheel.  It’s almost more like CMYK color mixing or doing printer lights on a negative.  Manipulating these sliders together, when you get it dialed in, produces a beautiful and lush color palette.  The other added benefit to splitting up the channels in this manner is that you can add serial nodes to each color channel and add in effects.  Imagine adding diffusion, grain, glow, noise reduction or some other effect, only on one color channel.   It’s really fascinating to experiment with adding grain and halation per channel.

3: Combiner Node: This is the node that takes the output from RGB and turns it back into one lane.  I have a theory that this node is also where the color magic happens. It may be combining the channels in a different way.

4: Saturation Node:  Often the image that get recombined is extremely saturated.  This node lets you dial that back to earth.  The colors will settle in nicely, and then you get a chance to go back and adjust the mix.  Try experimenting not only with Saturation, but “color boost” slider here too.  That can give some interesting results.  Use the Primaries / Color wheel panel. ( or what ever you like really… You can use color curves here too)

5: Contrast: This is where you put in your contrast into the Log Curve.   I use a combination of the Lift/Gamma/Gain dials and the luminance curves to get it where I like it. Use what works for you.

6: SKIN Node:  This node serves ONLY one purpose. You isolate the skin tones with the qualifier, and go back and double check your three strip mix on the Vector scope.  Like below.    This is a quality control node.   I don’t make adjustments here.


Everything beyond the Skin node is traditional grading.   Masks and qualifier adjustments, overall color grading, and the “look” you want to apply.  You could probably make a compound node out of the 3 strip section to make it simpler.  I like to personally keep them expanded to be able to dig back in.  I generally, do Contrast Node first, then Tint Node, then find the color balance with RGB and Saturation. The skin Node is last to make sure the humans look right.

Use the RealWorld11 Power grade to set the look of the starting point of color for each scene.   Then you can just work traditionally.

OK, so thats how it functions.
Have a blast!

 


PART II: The Shooting LUT:

Now, on to the LUT building section of this project.

Because, this 3 Strip process is just a manipulation of channels with no OFX in play, you can actually generate a LUT from it.  So the LUT in the google drive folder above, is actually utilizing the 3 Strip process.  It’s carefully crafted from test charts and a variety of footage to build a “do it all” on set LUT.  This also means, thats its not perfect overall, however its the most flexible LUT I was able to build.  More on that in a moment.

With the very generous support of Tim Kang of Aputure Lighting, providing me space to work in, I set out to design that onset LUT, that would use the full contrast range of the GFX100 II’s Flog2 gamma curve, as well as have a color palette that I found to be beautiful.  Now that I had a rough idea how the 3 Strip process worked, the first step was getting good footage into it.

It all boiled down to the following steps.

1:  LUT build for on set use.  This is to help me use as much of the Flog2 curve I could, to feed the post “Real World” 3 Strip process.
A: Color balance the LUT to neutral.
B: Contrast expansion of Flog2 to reach black and white points.
C: Contrast curve to add a pleasing feel to the image.

The way I did this was I shot some Tungsten and Daylight test images with charts and skin tones.   Then I built a scenario where the scene had true black and white in the same scene, a LED light with diffusion and a piece of shaded and boxed black jewelers velvet.   Then I collected a few various scenarios of footage on  GFX100 II.   Shots around the house, interiors, exteriors, the street, the desert, and the ocean.  I used a Sekonic C-800U color meter to measure the quality of the spectrum in the Tungsten and Daylight sections to maintain purity.

Then what happens is you start doing what Tim Kang called, LUT averaging.   You start with the Color charts and human face.  This point I need to create really clean colors, that are neutral.  I have to be able to put the tungsten look on the daylight shot and the daylight look on the tungsten shot and get minimal color shift.  At that point I split the difference between them and thats the color “accurate” balance.  The trick here is that there are two color accurate points of reference.  Since the camera is balanced to the light source and both light sources are accurate and full spectrum, you can trust that the reproduction will be faithful.  This LUT I am building will have to work for both daylight and tungsten, and it should not matter the light source so long as the spectrum is full.  The white balanced camera won’t be able to tell the difference. Then you save that power grade.

The setup:  There is little importance to the brightness and contrast of this image.  This is just to see the chart, and get perfect white balance.  Its basically still in LOG.  The only nodes manipulated are the TINT, RGB and Saturation in this phase.

One of the Color balance samples.

That saved power grade is then applied to the contrast test scenario footage. Without touching the color, you adjust the contrast node until black hits “0”, and white hit’s 100.   So now you have centered the color across two black body radiators, Tungsten and the Sun, and dialed in the black and white points of the sensor and log curve.

The Contrast test scenario

The last step in the LUT building is now developing the contrast curve.  Just because I stretched the white up to hit 100% and the black down to 0%, doesn’t mean the curve is nice to look at.  I took a ton of GFX 100 II footage and adjusted each one, individually, saving and passing the power grade forward.  Then cross referencing back to the beginning clips to see if the look still worked.  This is where the LUT averaging really starts to take effect.  In total, I made 52 versions.  I thought I was done at version 41, and named it REALLIFE_1.

Classic mistake.

10 versions later I think I’m happy with REALLIFE_11.  All in all, this process took almost 2 months to complete.   Next time with all the trial and error out of the way, I can do it in a much shorter time.

I hope you found this all useful.  Enjoy the LUT and Color workflow.  Thanks for reading.

-Timur

 

 

Subscribe
Notify of

 

This site uses Akismet to reduce spam. Learn how your comment data is processed.

2 Comments
Oldest
Newest Most Voted
Inline Feedbacks
View all comments
Daniel colmenares
1 month ago

Fantastic work Timur! Many DPs who end up going on a similar journey never put the time in to write an article and share their findings publicly. Thank you for doing the work and keeping the spirit of sharing and communal exploring and learning alive. You did a wonderful job of pulling the veil back a little bit and showing aspiring DPs the inner workings of what it takes to build a lut and why power grades are a much better solution to an off the shelf LUT. did you find that you had to do any hue vs sat… Read more »