To ensure an accurate result when using the P6K2Alexa/P4K2Alexa transform it is recommended you follow the camera setup and post workflow instructions below.

Camera SIDE

On the camera side the setup is very straightforward. And if you’re shooting in BRAW, in most situations you don’t really need to worry about these settings as they can be adjusted in post. However in some situations the ISO setting will be factor as that can affect how you expose the image, more on that below. If however you shoot in Prores, the correct settings are of more importance.

The recommended camera settings for Prores/BRAW for most shooting scenarios is as follows:

Gamma: Blackmagic Design Film
Gamut: Blackmagic Design
ISO: 800 is recommended, but any ISO will work
Temperature: 5600k (depending on filtration used)
Tint: P6K: +10, P4K: 0 (depending on filtration used)

Gamma and Gamut

The Blackmagic Design Film gamma and Blackmagic Design colour space preserve the bulk of the sensor data which makes them ideal candidates as the input for the Alexa conversion. If your footage is shot in BRAW make sure you decode to these settings. If you shoot in Prores make sure your camera is setup to record to these settings.

The PowerGrade version also accepts footage decoded as linear, see the usage instructions below for more details.

ISO

I find that ISO800 is the closest match to the Alexa. Not only because it matches the Alexa’s native base ISO of 800, but also because it narrows the gap between cameras when it comes to highlight handling. But you can shoot at any ISO appropriate for the shot, it doesn’t affect the accuracy of the transform.

Rating the P6K/P4k at ISO800 does increase noise slightly, but in my testing it’s only slightly more noise than an Alexa shooting 2.8K ARRIRAW.

Temperature and Tint

Temperature and tint is somewhat flexible. Under daylight or daylight balanced sources, with no filters in front of the lens, I recommend a temperature of 5600k and a tint of +10 for the P6K and 0 for the P4K. This is the closest match to the Alexa. However these settings will be different depending on the filtration used. More on that below.

Under non daylight sources it’s important to dial in the correct white balance. This is easy if you shot in BRAW. If you’re shooting in Prores I recommend getting as close as possible on set, then fine tuning with the offset wheel in Resolve. In general I dial in the big moves in the raw tab or on set, apply the settings to all clips, then fine tune shot to shot differences with the offset.

Filtration

One of the biggest factors that can affect the quality of your footage and the accuracy of the transform, is filtration in front of the lens. Variable NDs, IRNDs and IR cut filters can introduce colour casts. However, this is fairly easy to correct for. The easiest method is to shoot an outdoor scene with and without filtration, then in Resolve use the temp and tint controls to match the filtered shot to the unfiltered shot. These settings will be your new neutral temp and tint settings.

For example, the Hoya UV & IR Cut filter adds a slight green tint, but it can easily be offset by adding +5 Tint. So the new tint value for the P6K is 15, and 5 for the P4K. I also noticed that it adds a minor green/blue vignette which is more prominent on wide angle lenses. This can be corrected with a circular Power Window and the offset wheel.

Correct Exposure AND ETTR

Part of what makes Alexa footage look so good is correct exposure. This ensures deep rich colours, rich skin tones and correct contrast via maximised use of the sensor’s dynamic range. This means methods such as ETTR should be avoided.

ETTR is ok for cameras recording to 8bit codecs, but ETTR is unnecessary for cameras recording 10 or 12bits to high quality codecs like BRAW or even Prores 422HQ.

ETTR creates issues with differing noise levels and exposure not matching between shots in the same scene. This is due to the exposure being dictated by the brightest object in the scene. And if the brightest object in the scene disappears or changes brightness, ETTR dictates that you change your exposure. Which means shots from the same scene won’t match in exposure or noise level. What might be even worse, is that is possible to expose so far to the right that it is difficult to return correct contrast back to the shot, as the majority of the shot lives in the upper linear portion of the log curve.

A much better method than letting highlights dictate exposure, is to expose for the middle of shot, or middle gray, aka 18% gray. The theory here is that if you expose for middle gray on a sensor that has equal stops above and below middle gray, you’ll be able to accurately capture the entire dynamic range of the scene with correct contrast, with minimal or no clipped highlights and all at an acceptable noise level. And the exposure will be consistent between shots and scenes. With cameras like the P4K/P6K, it is possible to do this for most scenes.

False Colour

The easiest method to expose for middle gray is to use false colour. With false colour enabled on the P4K/P6K shooting at ISO800, anything that is highlighted green is being exposed exactly at the middle of the sensor’s dynamic range. Along with green the BMPCC also uses pink (1 stop brighter than middle gray) to help you expose skin. For most shots featuring people, all I do is place green towards the shadow side of the skin, and place pink on the lit side of the skin. Any skin tones between those colours will be right in the sweet spot. For darker complexions it’s possible place green further towards the lit side of skin to avoid overexposure.

For scenes that don’t feature people, it’s a bit more flexible. Generally I place green on or near the focus of the scene. But paying close attention to the brightness of that focus. Placing green on a white polar bear in snow will result in an underexposed image. Here you need to use judgement and experience to gauge correct exposure. And for this example I would probably look to place pink on the shadow side of the polar bear.

I also like to setup zebras to appear at 100%. Mainly as a final check to make sure that nothing of importance in the scene is being clipped.

How do you know when you have correct exposure?

If you can take your footage into Resolve and apply P4K/P6K2Alexa and without any adjustments the skin brightness looks correct, you can simultaneously see detail in the shadows and highlights, and you have no urge to adjust exposure, then your exposure is spot on.

For some projects shot by talented DPs, I can grade the entire project without adjusting exposure. Thats the level of accuracy possible with false colour.

If you need to correct ETTR or overexposed shots see the Solving Issues section below.

Installation and Usage

Resolve LUT Installation

Extract the zip file, open Resolve and bring up Project Settings. Navigate to the Color Management tab on the left and scroll down to Lookup Tables. Click the Open LUT folder and copy over the P6K2Alexa/P4K2Alexa folder. If you also want the all-in-one Rec709 versions you can copy the PxK2Alexa Rec709 Post-Production folder as well. Navigate back to Resolve and click the Update Lists button. The LUTs will now be accessible inside Resolve.

In-Camera LUT installation

The in-camera LUTs can be found in the PxK2Alexa Rec709 In-Camera and On-Set LUTs folder. For instructions on importing and applying LUTs on the P6K/P4K, check pages 85-86 of the BMPCC Operational Manual which can be found here: https://www.blackmagicdesign.com/support/family/professional-cameras

Using the LUT in Resolve

This is the basic node structure I use with the LUT.

Node 01 is noise reduction. I generally use Spatial NR with Mode set to Faster, Radius set to Small. Then under Spatial Threshold I unlink Luma and Chroma and leave Luma at 0.0 and set Chroma to around 8.0.

Node 02 is used for fine tuning the image balance. Generally to correct for shot to shot differences as the overall balance is best handled in the raw tab. If the footage is Prores, the bulk of the balancing will take place in this node. Since this node sits in BMDFilm log space I would use the offset wheel to make exposure or colour adjustments. Just pay close attention to exposure as it can cause the LUT to clip.

Node 03 is the P6K/P4K to Alexa_LogC transform LUT. Select either an ISO400 or ISO800 version of the LUT from the PxK2Alexa / PxK2Alexa LogC / Input Scale folder. If you’re footage is decoded at ISO400 or below, select the ISO400 LUT. At any ISO above 400, just stick to the ISO800 LUT. For the P6K I’ve included Balanced variations that remove the slight green tint typical of Alexa footage. In some situations the green tint can be too much. The P4K tends to handle such situations better and I saw less need to adjust the balance.

The gap between Node 03 and 04 this is where creative grading takes place.

Node 04 is the output LUT. This node handles the conversion of ARRI LogC to Rec709. Select a LUT from the PxK2Alexa / Alexa Rec709 folder or any other LUT designed for ARRI LogC. You can also use a Color Space Transform node to handle the conversion for extra flexibility.

PowerGrade Installation

To install the PowerGrades in Resolve, in the Gallery tab navigate to the PowerGrade 1 stills album. Adding the PowerGrades to this album will allow you to access the PowerGrades from any project and it also means you only have to add it once. Once selected second mouse button click in the gallery window background and select Import. If it doesn’t let you select a file, you might need to click the options button at the bottom of the import window and then select .dpx or .drx from the list, then try again.

Once installed the PowerGrades can be applied to the selected shot by middle mouse button clicking on the still in the gallery. Or with a second mouse button click and then selecting Apply Grade.

Along with the PowerGrades you’ll need to install the ARRI LogC to Rec709 conversion LUTs. Follow the LUT installation instructions above and copy the PxK2Alexa Rec709 LUTs folder to Resolve’s LUT folder. If you do this incorrectly, your footage will remain as flat log gamma after applying the PowerGrade. You will also get a missing LUT error message.

the P6K2Alexa PowerGrade

Node 01 is a pre-curve that modifies an ISO800 image ready for the Color Space Transform (CST) in Node 02. If your footage is shot or decoded at ISO400 you can disable this node. For any other ISO above 400, I would leave it on.

Node 02 is a CST node that transforms Blackmagic Design Film to linear. Node 01 and Node 02 can be disabled if the gamma is set to linear in the raw tab. But pay close attention to saturated colours with high contrast edges as they can cause artifacts when working with images decoded as linear.

Node 03 is for accurate exposure adjustments using the master gain wheel, which is especially useful when working with Prores footage. For example doubling the gain from 1.00 to 2.00 increases the exposure by precisely 1 stop. And halving 1.00 to 0.50 decreases the exposure by 1 stop. This exposure adjustment method can also be useful when working with footage that has been shot ETTR.

Node 04 is the 3x3 matrix and the core of the transform. This matrix lives in the RGB mixer and it aligns the P6K colours to match the Alexa. It can be difficult to make changes in the RGB mixer which is where Node 05 comes in.

Node 05 is the an approximation of the 3x3 matrix created using Hue v Hue/Sat Curves. It’s a lot easier to edit, but it’s not as elegant of a solution as the 3x3 matrix. Make sure you only enable either Node 04 or Node 05, but not both.

Node 06 is a CST that transforms the image from linear into LogC. If you have any colours that are clipping or causing issues, try enabling Gamut Mapping in the CST of this node.

Node 07 is the slight tints the Alexa exhibits in the shadows and highlights.

The Gap between Node 07 and 08 is where creative grading takes place.

Node 08 is the highlight roll-off curve. It’s the only creative part of this PowerGrade, hence why it is disabled by default.

Node 09 handles the conversion from ARRI LogC to Rec709. Select a LUT from the P6K2Alexa Rec709 LUTs folder or any other LUT designed for ARRI LogC. You can also use a CST node to handle the Rec709 conversion for extra flexibility.

I like to treat the footage as if it was shot on a real Alexa and it tends to respond in an almost identical way. The PowerGrade (or the LUT version) allow me to use the exact same grades and workflows I’ve developed for the Alexa, on P6K footage. And usually with no modifications.

Following my standard Alexa workflow, for most grades I remove Nodes 08 and 09 and replace them with a Film Print Emulation (FPE). Either a real FPE LUT or one of my FPE PowerGrade rebuilds. I select all the nodes from 01-07, and group them in a Compound Node to clean up the node graph. And generally once the project is underway, I don’t make adjustments to any of the nodes inside the Compound Node.

All grading takes places after the Compound Node (or Node 07) and before the FPE.

Continuing with the standard Alexa workflow I’ll sometimes use a CST node before the FPE to convert the colour space from Alexa Wide Gamut into Rec709, ready for the FPE. In the CST I select the Input Color Space as Alexa and the Output Color Space as Rec709. LogC should also be selected as both the Input and Output Gamma. Pay close attention to gamut issues caused by saturated colours, you may need to switch on Gamut Mapping.

Similar to the LUT version of the PowerGrade I always put a noise reduction node before Node 01 and I use the same settings as listed in the LUT section above.

the P4K2Alexa PowerGrade

The basic node structure is the same for the P4K version. The only difference is the omission of the Hue v Hue rebuild of the matrix. If you would like to see this included in future versions, let me know.

P6K2Alexa/P4K2Alexa ACES PowerGrade

The node structure is also similar for the ACES version of the PowerGrade. The main difference is Node 07, which approximates the WDR look inside ACES.

To use the ACES version make sure you setup Resolve in ACEScct mode, then apply the PowerGrade as normal. At this stage the PowerGrade only works with BRAW footage as Resolve doesn’t have an IDT for Prores P4K footage.

Other Software

I’ll be updating this page with usage instructions for other software. In the meantime get in touch below if you need help.

Solving ISSUES

Correcting ETTR and Overexposed shots

Questions, Comments, Support

For questions, comments or if you need LUT/PowerGrade support feel free to contact me at support@juanmelara.com.au