Color Correction: Tools & Technical

Question: What do you think this color represents? It’s a sample taken directly from a piece of footage I was given to color.

Answer: Skin tone!

After all the talk on how subjective our eyes can be, let’s talk about objective ways to measure a video signal. Scopes are visual displays of various components of an image and they are a very useful tool when it comes to color correction.

Resolve has scopes built in, and for casual use there is no problem using them, but there are a couple reasons you may benefit from using scopes outside of the color application. External scopes simply take your video signal as an input, usually via SDI or HDMI, this means there is minimal GPU strain involved on processing the scopes themselves. If you’re on an underpowered system, or need every last ounce of your GPU for computing the grade, handling the scopes’ processing externally can be a noticeable improvement, and they’ll always play realtime. There’s also typically more power in a dedicated outboard scope. Scopebox provides tools for assessing RGB gamut errors (Scopebox channel plots help these sorts of errors or if you have the money go for a Tek Double Diamond); other scopes like HML balance help you remove color casts quickly; but they’re also highly configurable in that you can enlarge the data trace and position things how you need them for your setup. Newer scopes can also chart changes over time, provide false color overlays, superimpose traces, and provide target markers. In addition to all these features, it’s always wise to let your scopes monitor the same signal chain your grading display is using. Levels issues or problematic cabling will affect what you see on your grading display, but Resolve’s software scopes won’t help you spot it.

Scopebox (Outboard Software Scopes)

ScopeBox is a piece of software that turns your computer into a very professional set of scopes. I run it on a laptop and use the small, bus-powered BlackMagic mini recorder hardware to get the video signal into the computer.

Some NLEs like Premiere and Resolve can send the video signal via software to Scopebox on the same system. This might not help you much when it comes to reducing system strain, but it’s an easy way to get the power of Scopebox on a single system. Scopebox is also a handy tool during production. It’s a very full-featured signal monitoring tool for creative work and you can even record the signal. Be aware that it can really tax your system and drain a laptop battery quickly however.

In 2019, Scopebox switching pricing strategies to more of an annual subscription approach.

Vectorscope

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Measures an images saturation. No saturation at the center and fully saturated at the perimeter. Hues are represented at various locations around the scope, just like you’ll see in Resolves primary grading controls. The boxes identifying each hue show the extents which should not be exceeded for a signal to be “broadcast safe”. This actually varies based on the luminance of the color, but it’s an easy rule of thumb to just draw a line connecting the “hue dots” and not let you saturation exceed that. Some vectorscopes also have a “skin tone line” which can be helpful to see where your subjects skin color falls objectively. Using offset to “center the blob” is an easy way to quickly compensate for color casts.

Waveform

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Waveform represents luminance. In FLAT view it combines luma and color signals. It correlates, left to right, with your image and shows brightness bottom to top. So if you have a bright white window on the left of frame you’ll see a bright white ‘trace’ on the waveform’s left side near the top.

RGB Parade

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A waveform broken into R,G and B channels shows the individual luminance of red, green and blue. It’s a very useful tool when you’re trying to eliminate color casts because anything black, white, or gray should line up horizontally since it contains equal parts red, green and blue.

scopebox_screenshot_joey_danna
Joey D’Anna’s ScopeBox setup

There is some confusion about scopes in Resolve since it displays “code values” for 10 bit data rather than traditional “video levels”. The idea of video levels is related to voltages in the analog days and is somewhat archaic, but many traditional video professionals still relate to such levels in terms of exposure. Caucasian skin tone, in an average exposure, generally sits around code value 600 on Resolve’s scopes. This is only relatively useful information, however, as the mood of the scene can drastically alter this number.

Resolve: Color Grading (Blackmagic Introductory Video)

Frame.io Workflow Document

There are several reasons Resolve is widely regarded as an excellent color application. Before it was a VFX, audio, and editorial tool, DaVinci Resolve was an expensive, hardware based color timing system. It’s roots in color are still manifest today in a very robust set of color tools widely used across a variety of Hollywood feature films.

Node Types & Usage

Node types in DaVinci Resolve

Clip vs. Timeline Grades

Resolve allows you to apply a given operation across the entirety of your sequence via the “Timeline” node tree. Common adjustments include noise reduction, sharpening, soft clipping, and gamut limiting (via a “Gamut Mapping” node set to rec709).

Grouping

Pre-clip > Clip > Post Clip

Memories, Stills & Power Grades

Stills” are comprised of two components:

  • .dpx reference images on the hard drive (a screenshot of the current look)
  • Accompanying grade metadata that can be copied anywhere for recreation of all or part of the node tree
  • Opt+Cmd+G grabs a still (and sends it to whatever folder is selected–global powergrades or local stills)
  • Double-click a still to wipe it. Doesn’t work with power grades shared between projects
  • Middle-click a still to apply it.

β€œPowergrades” are simply stills that globally can be accessed from any project–looks you want to save in an ever-accessible database. I find this massively useful for storing a set of creative grades as well as grades that apply across seasons of a show in different projects.

β€œMemories” are stills that you can recall with control panel or one-button press for convenience–effects you use a lot. They’re really the same thing as “stills” just with a different, more convenient way to access. I use them a lot for quickly storing temporary looks. Alt+Number key will save a memory and Cmd+Number Key will recall that memory.

Versioning

Resolve has a powerful ability to test different grades and easily compare them via “versions”.

Cmd+Y adds a new version and cmd+b (before) and cmd+n (next) allow you to step through the versions.

The “Split Screen” feature can be activated via the grid-like icon in the upper left. This allows you to easily compare different versions side-by-side. You can also use the feature to compare multiple clips in a variety of ways. I used to use the ‘neighboring clips’ feature, but now rely more on the “Clips” grid view in the dual panel layout to compare neighboring clips and how well they match.

The highly-useful “Split Screen” toggle

Keyframing

I find the “Color” mode most useful for keyframing as it will auto-key only the selected node’s parameters.

Tracking & Stabilization

Resolve has one of the industry’s strongest trackers.

Cmd+T to track forward and Alt+T to track backward.

The “Frame” mode makes manual additions to your tracks much simpler.

Remember to disable any effects that slow down playback as they’ll massively (and often unnecessarily) slow down your track speed.

Change the mode in the upper left to invert the tracker for stabilization (there are alternative ways to stabilize post version 16)

Misc Useful Things

  • Having a mouse with a middle click button is imperative for speed in Resolve
  • – and + keys allow for copying the previous clip’s grade or two clips back.
  • “Color Trace” is a useful tool for copying grades between projects, even where timecode and/or reel names do not match
  • There’s a built-in color chart matching tool which is marginally useful
  • ‘g’ adds a flag defaulting to color of flags on edit page but double click to change flag color
  • Hamburger menu: Convert to bezier for making circular power window editable. From the same menu you can save windows as presets.
  • Put tape on BlackMagic controllers for quicker muscle memory. You’ll immediately feel the difference in the buttons.
  • Destructive clipping happens via LUTs, Soft Clippin and any Vs Curve operations
  • Use the “prev memory” button on the BM mini panel or via keyboard shortcut to see the clip’s grade when you first navigated to it
  • Hamburger Dots on the viewer window enable you to “gang” the relationship between the selected clip and the timeline reference wipe clip. This can be convenient when you’re frequently trying to compare to the previous clip.
  • Using Gamma 2.4 is fine for broadcast and web both
  • Changing clip color can also be useful, especially in tandem with clip filtering (accessible via the carrot next to “Clips”)

Primary vs. Secondary Grading

Primary grades affect the whole frame universally in much broader strokes.

Secondary grades are selective about which portion of the image is affected. “Power windows”, Hue vs. Saturation curves, or the qualifier are all examples of a secondary grade:

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