Color Science for Video Editing

Specifics are mostly for BlackMagic’s Davinci Resolve.

What is a Color Space?

Colors can be created by adding (or subtracting) certain key colors, or primaries. The “strength” of these primaries can be mapped to geometric coordinates on a shape. The “area”, or boundary of the patch between the primaries defines the gamut - or maximum range of colors that can be represented by (vector) addition and scaling of the primaries. This assumes that scaling is limited to 0<=1.

Choosing different locations for the primaries creates different color spaces, with different gamut sizes. More info.

Some common examples:

  • sRGB - Web, print
  • Rec709 - HDTV
  • DCI-P3- Digital cinema; Apple uses a variant Display P3
  • Rec.2020- UHD + HDR (wide Gamut.)

Color spaces are usually used for a specific intent:

  • scene (capture/from a camera, CG software…)
  • display
  • intermediate (editing)

Intermediate/editing are usually linear. Scene/display may be logarithmic.

What is White (D points)?

“White” is typically defined as the emitted light color of an idealized non-reflective, opaque body at a defined temperature in degrees Kelvin. Details here.

For defining color spaces, we need to know how a “reference” white is represented. The reference white is usually a “D” number - eg D65. This means “white” in the colorspace will match a 6500K idealized light emitter.

More info here.

Gamma

Human eyes don’t see brightness (luminance) in a linear fashion. So for various reasons (e.g. to make linear changes in color coordinates appear linear; to keep measurement accuracy (more digital bits) for values we’re more sensitive to) a non-linear curve/mapping is applied to the color coordinates by the display device; this is the gamma.

References

Color Spaces for Videography

Unfortunately color space info and gamma is not always included in different digital containers.

Recommendations are to include colorspace and any applied gamma in file names.

Capture/Input

SD

  • JPG, PNG, Inkscape, Gimp, Illustrator, Photoshop, Scanners… probably sRGB
  • RAW… up to each camera manufacturer.

HD

  • Rec709 - most SD/HD video cameras
  • Display P3 - Apple
  • ??? - insta360

UHD

  • slog1/2/3 - log format for HD video
  • hgl1/2/3 - log video for UHD/wide Gamut (HDR)

Computer Generated Images/Video/Renders

  • ACEScg

Color Grading/Editing

  • ACEScc
  • ACEScct - same as ACEScc, but with a gamma curve “toe” near black
  • Davinci Resolve Wide Gamut

Archival

  • ACES2065-1

Color Correction vs Grading

Grading == “visual style”; may not be accurate to reality; artistically tweaked

Correction == taking raw inputs and adjusting them so that they are as close as needed to the “real” scene.

Usually correct all incoming media to have a neutral, “realistic” look, then can apply the same adjustments across all clips to consistently achieve the desired style.

More info here.

Camera Color Space Setup

some other notes for capture setup… needs to move to it’s own page(s)

Set shutter speed to 2x frame rate for expected motion blur (180 degree shutter angle.) See here for details.

Understand your exposure triangle; it’s always a compromise between

iOS

  • will capture in Display P3
  • Gamma: ???

Insta360

  • use the log profile?
  • Gamma: ???

Sony

NLE (Resolve) Setup/Process for Color

*Note: seems some references to a “yellow tint” with ACES/RCM on OS X. Try googling ACES + OSX + Yellow + setting display output colorspace to Display P1(?)

  • enable color management
    • see ACEs vs RCM below
  • choose the colorspace for the project.
    • usually linear
    • may be wider than the gamut of your monitor
    • ACEScc/cct/cg or Resolve Intermediate Wide Gamut (see
      here.
  • specify the output colorspace and gamma(!) for the project
  • import media
    • make sure it’s set to the correct scene referred (input/what was recorded) colorspace & gamma!
  • color correct
    • lift, contrast, whitepoint
  • color grade
    • figure out the style; apply it to all clips
    • Hint: lots of colorists like the Arri log color space for grading; gives the controls a certain “feel”. Can do that in Resolve by adding a color-space-convert node to Arri-log-C, then a serial node for the style, and then another serial node to do the color-space-convert back to project color space.
  • output to destination (display referred) color space and gamma

Resolve Color Hints

  • if no clip is selected, you are adding color nodes for the entire timeline; great way to adjust entire color corrected timeline (which should do the right thing on all clips.)
  • set up two basic contrast and balance nodes on one clip, then select all, and apply == quick way to set up a template set of common nodes on all clips
  • as you add correction nodes to a clip, you can use a command in the colour menu to append the last node you added for this clip to all others(!)

Important GOTCHA Re LUTs

  • LUTS only give conversion points for a limited number of colors; rest are interpolated. Thus LUTs can be lossy!
  • LUTS assume a given input colorspace, and output a certain colorspace
  • SO YOUR PROJECTS COLORSPACEs (editing and output) NEED TO MATCH the LUT
  • Resolve can generate LUTs from a given set of color transform nodes
    • faster processing
    • can round/overflow (ie lossy)
    • make sure you include input and output colorspaces in the name!

ACES vs Resolve Color Management (RCM)

  • for “generators” creating clips to be edited/graded in resolve, set their output to ACESccs/cct/cg (eg Blender, Natron, …)
  • If edited & graded clips from Resolve are being passed along to someone else, set up ACEs color management in the Resolve project settings
  • if Resolve is the last step, Resolve Color Management + Resolve Wide Gamut intermediate Colorspace may be best; will have support for more input colorspaces
    and gamma corrections.
  • https://www.youtube.com/watch?v=TxCGR_gNTME

Worked Examples

Setting up ACES in Blender

Misc

DisplayCal is free software that can use several commercial color calibration hardware devices. In some cases it offers more features than the included software.