Display Calibration Best Practices

Target Audience:

This document is intended for Netflix Content, Fulfillment, and QC Partners that perform any degree of picture quality analysis on Video content provided as source files to Netflix. This is for Standard Dynamic Range (SDR) workflows only.

Goal:

The wide variety of display types and viewing environments can lead to inconsistent quality results, unless a set of guidelines is put into practice which adhere to a common standard. The guidelines provided below will need to be adopted by each contributor to the Netflix Digital Supply Chain, to ensure consistent quality.

Viewing Environment:

Section 1 of Annex 1 of Recommendation ITU­R BT.2035 describes reference viewing conditions for HDTV. Netflix recommends adherence to the guidelines contained therein.

Of particular note:

a)

Room illumination:

10 Lux

b)

Chromaticity of background:

D65

c)

Ratio of luminance of background behind picture monitor to peak luminance of picture:

maximum of 10% of reference white value

 

Display Technology Resolution Requirements:

This describes the minimum native raster resolution capabilities for each resolution category.

  • SD: SVGA (800x600) for computer display or NTSC and PAL broadcast monitors
  • HD: WUXGA (1920x1200) for computer display or HD broadcast display (1920x1080)
  • 4K/UHD: WQUXGA (3840x2400) for computer display or 4k UHD display (3840x2160) (UHD only)

Display Technology Color Gamut Requirements:

This describes the proper color standard for each resolution category.

  • SD: Follow Recommendation ITU­-R BT.601­-7
  • HD: Follow Recommendation ITU­-R BT.709­-5 for HD and computer displays
  • 4K/UHD: Follow Recommendation ITU-­R BT.709-5­ (with future need for Rec 2020)

Calibration interval:

All displays used in the evaluation of Netflix content shall have periodic calibration performed at a minimum interval of 90 days. Critical viewing environments, such as Color Grading and Final Editorial/Finishing or Visual Effects suites should be calibrated at a minimum interval of one week.

Display Connection Topologies:

  • Topology 1: This applies to displays with SDI connections, such as broadcast monitors, or HDMI and DVI connected displays with no computer managed brightness, contrast or color control.
  • Topology 2: This applies to displays that are either integrated into a computer workstation or are part of a workstation with dedicated display (MACBOOK PRO, IMAC, MAC PRO, AVID, PREMIERE etc). The workstation OS or application manages the display parameters via the graphics interface.

Calibration guidelines for Topology 1

Displays in this topology typically expose full controls for brightness, contrast, and color and are not managed through a graphics card in a dedicated workstation. Black level and reference white level adjustments often interact, so they should be repeated to ensure that both are set correctly. Perform the adjustments as follows.

Calibration adjustment order:

  • Black Level set
  • Reference White level set
  • Black level set
  • Reference White level set and Luminance measurement
  • Gamma measurement
  • Color Adjustments

Brightness (Black Level) Adjust ­ (use calMAN VideoForge brightness test pattern)
Brightness adjustment is judged by visual evaluation of one of the multiple design PLUGE patterns available from different sources (Picture Line-­Up Generating Equipment). The common ingredient of all these patterns is that they have blacker­-than­-black (below digital 16 in 8 bit channel), black, and just­-above-­black test bars.

Adjust Brightness (by visual test pattern evaluation):

  1. Display a Black Level (or Brightness) test pattern.
  2. First, increase the display's Brightness control enough to be able to see all the dark picture levels in the test pattern.
  3. Then, reduce the Brightness control just enough to make the two darkest parts of the pattern blend together.

(For patterns with numbered dark bars, reduce Brightness slowly until the 1-­16 numbered bars as dark as the background)
Here is a video guide to the above steps: 

Adjust Contrast (by visual test pattern evaluation):

  1. Display a White Level test pattern.
  2. First, increase the display's Contrast control to the point where either color shift begins, or the brightest gray test pattern bars start to blend together with the 100% white background.
  3. Then, reduce the Contrast control enough to be a step or two below the point where either color shift begins or the brightest gray test pattern bars start to blend together.

(For patterns with numbered bright gray bars, it is more important to avoid color shift than to preserve the bars above about 240).

Repeat Brightness (Black Level) Adjust

Repeat Contrast (White level) Adjust

Measure Reference White Level Luminance value:

Many displays provide a means of setting the overall display luminance, independent of the Contrast control. In LCD displays, this is usually called Backlight; in plasmas, it is called Cell Light. The backlight should be adjusted to produce the desired display luminance at 100% stimulus (peak white). Adjusting a display’s backlight is desirable to establish picture luminance levels that are most appropriate for the room viewing conditions.

Recommended Display Luminance Levels:

  • Bright Room: 150­-250 cd/m2(44­-73 fL) Bright Room (casual viewing in public area)
  • Dim Room: 100­-150 cd/m2(29-­44 fL) (acceptable for less critical viewing)
  • Dark Room: 80­-100 cd/m2(23­-29 fL) Reference (optimal for critical viewing)

Use a video test pattern that provides reference white level (235) within a window area of 10% of total picture area (example: 32% of width x 32% of height yields rectangle with ~ 10% of total area). Measure the Luminance value with a tristimulus colorimeter or spectro-radiometer and adjust the backlight control to achieve the appropriate level.

Perform Full Color Calibration

We have two topologies to consider.

  • Topology 1: SDI attached displays.
  • Topology 2: Computer Graphics card attached.

Netflix recommends using Color Calibration software from Spectracal  (CalMAN5 or later). Minimum software required for calibrating displays used in either topology, using the Netflix authorized workflows, is CalMAN Ultimate. Minimum hardware required is Spectracal C6 Colorimeter (or compatible equivalent) and a test pattern generator under CalMAN control, such as VideoForge products.

The goal of color calibration is to minimize the difference between the perceived color and the intended color (target). This is typically measured in units of dE2000, or simply dE. A unit of dE is considered to be roughly equivalent to a “just noticeable difference” or JND and takes into account the human eye’s varying sensitivity according to wavelength (color).

After calibration, the dE values must be within the following limits as reported by CalMAN:

  • Max deltaE should be less than 5
  • Avg deltaE should be less than 3.

It is important to calibrate the display for Video work where the color standards are as follows:

  • ColorSpace : D65 white point Color Primaries, Coefficients, and EOTF
  • SD : ITU­R BT.601­7 with EOTF (gamma) as per: ITU BT.1886
  • HD and UHD: BT.709­5 with EOTF (gamma) as per: ITU BT.1886

At the start of each calibration session, please complete the information in the Calibration Setup Step so as to properly identify the display device being calibrated as well as other details that will be presented in the final report.

Display Calibration Resources are available on the Partner Help Center under Display Calibration Best Practices.

Here you will find CalMAN Workflow & Report Installation Instructions as well as the latest revisions to the workflows and reports used in the following procedures.

For Topology 1, use the CalMAN Netflix Video Monitor workflow to review and correct the display Grayscale and Color Calibration settings.

  • Ensure that the SDI or HDMI input used for calibration is the same as used for normal day to day work and that any display memory settings that include calibration parameters are properly saved.
  • Save and Publish both a PDF and JSON report of the Calibration session for this workflow.
  • Please include “topo 1” in the file name of the report.
  • Send reports to mep.support@netflix.com

For Topology 2, use the CalMAN Netflix Computer Monitor workflow.

Displays in this topology typically do not expose controls for color or gamma, but are managed by the attached computer and graphics card.

  • This topology requires the download and installation of “Client 3” software pattern generator and ICC profile manager, which runs on the Mac or PC host to which the display is attached.
  • Save and Publish both a PDF and JSON report of the Calibration session for this workflow.
  • Please include “topo 2” in the file name of the report.
  • Send reports to mep.support@netflix.com

All Topologies:

  • Post calibration: The color controls should not be adjusted. Small adjustments to brightness and contrast are permitted but must avoid clipping at either end of the luminance range. It is best to ensure that full range of grayscale is visible via test patterns before work sessions. Such patterns should be made available for the person using the display for working on Netflix content. Brightness and Contrast patterns are available on the Partner Help Center as movie files.
  • Quicktime Caveats: Popular movie file formats such as Apple PRORES variants and other Quicktime wrapped codecs are frequently used in post production workflows. While such files are capable of carrying the full range of luminance and chroma values, the Quicktime decoder pipeline found on Macintosh computers will clip these values to “legal range”.

Legal range is luminance between 16 and 235 with chroma range 16 to 240. (8 bit systems)

The main effect of this clipping action is that you lose visibility of these extreme values. For example, video that was improperly converted from RGB or other image file formats to Video (Y, Cb, Cr) could have scene elements in these ranges, such as graphics or dark objects. It is best to see these elements and know whether they are out of legal range, as an indication that a color conversion has been done incorrectly. Corrective action can then be taken.

Therefore, it is important to know whether your media player and display are capable of presenting such out of range levels.

We recommend using the procedure found on Backlot - ­Netflix Video Range Verification presentation

Note 1: The Quicktime decoder function found on PC workstations does NOT have this clipping limitation. It can faithfully reproduce the full range video signal to a locally attached display.

Note 2: Macintosh workstations, employing a professional video I/O card, such as AJA products or Black Magic Designs will also faithfully deliver the full range of video levels to connected devices such as VTR’s and Picture Monitors (Display Topography 1).


Change Log:

2017-03-21

  • Revised section "Target Audience" to specify that these best practices are intended for Standard Dynamic Range (SDR) workflows only.
  • Revised section "Viewing Environment" – added the ratio of luminance of background behind picture monitor to peak luminance of picture (maximum 10% of reference white value).
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