Broadcast, cinema and streaming requirements for PNG CICP tags in HDR/SDR production

Hi All,

As we discussed yesterday, here the reasons why broadcast and cinema productions require explicit CICP tags in PNG along with ST.2086, MaxCLL/MaxFALL.

Current HDR productions produce graphics in SDR because there is no way expllcitly signal the transfer function of HDR and SDR in either PNG or TIFF (with the exception of a newer ICC specification which can be accidentally and easily stripped from a file). Video wrappers and modern codecs all have a way to signal CICP (H.273) which carries information on transfer function, color primaries, matrix coefficients and signal range.  Still graphics content creators and archivists need the exact same functionality as motion video in order to avoid errors and automate conversions.

ST.2086, MaxCLL/MaxFALL provides two methods which can optimize tone mapping that occurs on a target display. ST.2086 specifies mastering display characteristics.  MaxCLL/MaxFALL specifies content luminance characteristics. With the combination of both sets of static metadata target(consumer) displays can avoid clipping that would otherwise occur if the mastering display has superior capabilities in peak luminance and color gamut range vs a target display. Clipping is to be avoided in order to avoid a loss of detail or unintended artifacts.


Below in another simplified form

Benefits of adding CICP signaling to PNG for content creators:

  *   Identifies video formats explicity for display and software by identifying:
     *   Color primaries of content
     *   Transfer function of content
     *   Matrix Coefficients (if PNG stores other color representations in the future)
     *   Signal Range (Full or Narrow/Limited)
  *   Facilitates conversion automation by identifying source format so correct conversion is selected towards a known output format (which can then include new CICP signaling matching the output format)
  *   Allows for proper display of content on HTML canvas which includes NextGen(ATSC3) broadcasts which is the new over-the-air broadcast method being deployed currently
  *   Allows for proper display of thumbnails in OTT (streaming) device application interfaces

Benefits of adding ST.2086:

  *   Provides a simple method for identifying specific luminance capabilities of the display content was created on (Mastering Display) so that a relationship can be established between source and target displays for optimal tone mapping
  *   This is especially useful because the typical mastering display(source) is of higher peak brightness vs the consumer display(target) so a knee (vs clipping) may be necessary to limit highlights.
  *   Clipping should be prevented to avoid loss of detail or other unintended artifacts.

Benefits of MaxCLL/MaxFALL in PNG:

  *   Provides a basic method for identifying specific luminance characteristics of the content itself which allows for optimized tone mapping on displays with lower peak luminance capabilities.
  *   Clipping should be prevented to avoid loss of detail or other unintended artifacts.


….I hope this helps…..

Chris Seeger
Director, Advanced Content Production
Office of the CTO
NBCUniversal, LLC

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