Log and RAW Workflows for Digital Cinema Cameras

A growing trend for digital cine cameras is their ability to record in multiple formats. For example, Blackmagic’s new URSA and Mini URSA announced at NAB support several types of RAW formats plus compressed ProRes.

The Blackmagic Cinema Camera, supports ProRes 422 and DNxHD plus “lossless” compressed CinemaDNG. ProRes can be recorded with either of two gamma curves applied: REC709 (video dynamic range) and logarithmic (film dynamic range). Figure 1 shows the BMCC’s recording options.

Post-production workflows for these advanced cameras will be more complex than those for ENG/EFP camcorders using traditional compression systems. These workflows require specialized knowledge and can be time consuming.

Figure 1. BMCC Recording options.

Figure 1. BMCC Recording options.

De-Bayered—REC709—Compressed

Figure 2 presents a schematic illustrating the data-flow within a BMCC. The right path shows the serial-RGB signal from a BMCC’s CMOS sensor de-Bayered from 2432x1366 photocites to a 1920x1080 frame. In “video”mode, the camera applies REC709 gamma to these 4:2:2 Y’CrCb data, which are then compressed by a ProRes 422HQ or a DNxHD (220Mbps) codec. The 10-bitcompressed data are recorded by an SSD. Because recordings are standard ProRes or DNxHD, they can be edited as would any other compressed format. They require no special post workflow.

Figure 2. Flow diagram

Figure 2. Flow diagram

De-Bayered—Log—Compressed

Again referencing Figure 2, the middle-path shows RGB data de-Bayered to 1920x1080 pixels. In “film”mode, logarithmic gamma is applied to the de-Bayered 4:2:2 Y’CrCb data. These data are compressed by a 10-bit ProRes codec and are recorded by an SSD.

Log ProRes is imported into your NLE the same way as REC709 ProRes is imported. Begin by appending footage into a timeline. The difference is seen when viewing a clip from a source Event or in a Timeline. As shown in Figure 3, a frame of log ProRes appears washed-out. (Image courtesy of the Diamond Brothers.)

Figure 3: Log curve results in a washed out image.

Figure 3: Log curve results in a washed out image.

To obtain maximum dynamic range from each log clip, software such as FXFactory sold by Noise Industries is employed. Drag the Curves function from the Natress Levels and Curves collection onto a clip.

As shown by Figure 4, you first set Log Mode to “Log to Video then Curves.” With this setting, log ProRes is mapped into REC709 space. You have a choice of three mapping functions: Log Cineon To Video (log C), Log B To Video, and Log A To Video. Each creates a subtly different dynamic look. I prefer using log A, although others may prefer log C.

A linear curve with five nodes will appear superimposed over the visible image. (Figure 5.) These nodes appear in the waveform monitor as five luma peaks that one disregards.

Figure 4: Linear curve.

Figure 4: Linear curve.

Adjust the five nodes to obtain maximum dynamic range. Figure 5 displays the image that results from pushing the right-most four nodes higher. The cloud detail which might be clipped to white without log recording, is fully visible. Click the Show Curves button to disappear the superimposed curve.

Figure 5: Increase image brightness.

Figure 5: Increase image brightness.

RAW—Lossless Uncompressed

The left-path presented in Figure 2 shows the 2.5K CMOS sensor feeding logic that creates CinemaDNG data. These 12-bit data are recorded to an SSD.

Several applications can handle CinemaDNG files. These include DiVinci Resolve (from Blackmagic) and Adobe After Effect’s RAW importer. I used After Effects for this article.

After launching AE, go to Preferences and choose Import>Sequence Footage. Set the Frame Rate to 24. Click OK. Now set the Files>Project Settings. Set Depth to “16bpc” which defines the project to have RGB channels with each channel utilizing 16-bits. Click OK.

Figure 6: Files > Import File.

Figure 6: Files > Import File.

Then, as shown by Figure 6, issue the Files>Import File… command. Now browse to a folder of DNG frames. Select the lowest number frame and confirm Format is Camera Raw. Also, confirm Camera Raw Sequence is checked. Click Open to import the clip and auto-open the Camera RAW window. The frame will be de-Bayered to create an RGB image.

Figure 7: White Balance and exposure controls.

Figure 7: White Balance and exposure controls.

Figure 7 shows the RAW control panel with white balance controls that are by default set to “As Shot.” This footage, courtesy Marco Solorio (©2012, OneRiver Media) looks perfect. Too perfect for use in, for example, a noir production. Figure 8 shows the scene with the Custom color temperature dialed down to 2700°.

Figure 8: White Balance set to 2700°.

Figure 8: White Balance set to 2700°.

Next, a slight S-curve is applied to deepen shadows and add punch to the highlights. This is done with another panel as shown in Figure 9. When you finished grading the RAW frame, click OK to make all frames in a clip share the same settings. This type of adjustment is called a “one-light” grade.

Figure 9: S-curve Applied to RAW.

Figure 9: S-curve Applied to RAW.

Next, issue the Composition>New Composition command. Set Preset to “Custom” and dial in 2432px and 1366px. Now, set the Frame Rate to 23.976 and click OK. See Figure 10.

Figure 10: New Composition Command.

Figure 10: New Composition Command.

Double-click the clip so you can see it in the Viewer. Issue the Composition>Add to Render Queue command. Set the Output Module to “Custom: ProRes 4444.” Doing so defines a conversion of 12-bit RAW frames using floating path math to 16-bit values that are exported as ProRes with 4:4:4 color sampling. Lastly, render the composition. It will take some time to de-Bayered each frame.

Now launch your NLE. Figure 11 shows the import dialog box for FCP X. By creating a proxy (ProRes) file at import, editing will be done using this performance-oriented file.

Figure 11: FCP X Import Dialog Box.

Figure 11: FCP X Import Dialog Box.

During export from FCP X, ProRes 4444 source files are written to disk. (Effects and composites must, of course, be decompressed—from ProRes 4444—to RGB floating point. These segments will be compressed to ProRes 4444 during export.)

While pre-processing RAW isn’t difficult, it is very time consuming. Working with log ProRes is far faster because the de-Bayering is done in-camera rather than in software on a computer.

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