HDR and Dolby Vision

MaxCLL and MaxFALL

The two light-level values in HDR metadata

These are the two numbers people most often want to change, usually to make a display tone map differently. Both are claims about the content, and on the Diva you can read what arrives and send something else.

MaxCLL is the maximum content light level: the brightness of the single brightest pixel anywhere in the title, given in candelas per square metre, which everybody calls nits. MaxFALL is the maximum frame average light level: take the average brightness of every frame, then report the highest of those averages. A brief specular highlight can push MaxCLL to several thousand while MaxFALL stays at a couple of hundred, because one very bright pixel barely moves a frame average.

Both are static values in the HDR10 metadata, measured once when the title was mastered and sent unchanged for its whole duration. A display uses them to decide how much to roll off: content claiming 4000 nits shown on a 700 nit panel needs far more compression than content claiming 1000. Both are optional, and both are frequently zero or plainly wrong, in which case a display falls back to the mastering luminance figures or to assumptions of its own. That is the reason people want to override them.

Setting MaxCLL and MaxFALL on the HDfury Diva

They are two of the fields in the custom HDR metadata generator in the HDR/DV section. MaxCLL is valid from 1 to 65535 and MaxFALL from 1 to 65535, and they sit alongside EOTF, Primaries, White Point, Max Luminance and Min Luminance. Define your values, click Create IF to build the infoframe, and the hex appears in the text box.

Nothing goes out until one of the custom HDR mode boxes is ticked. Use custom HDR for TX0 and TX1 injects unconditionally and ignores whatever the source sent. The HDR10 variant, set hdrcustomhdr10only on, applies your values only when the input is already HDR10, which is what you want when the aim is to correct a badly authored disc rather than to force a display into HDR mode. Send HDR then changes the values without stopping injection, so the television does not resync each time you try a different number.

Read what arrives before you replace it

CAPTURED HDR METADATA at the top of the same section shows the source infoframe in hex and deciphered into readable form, so you can see the MaxCLL and MaxFALL a title is actually claiming before deciding they are wrong. The OLED HDR INFO page carries the same information for a glance from the rack, and EXPORT CONFIG in the CONFIG section writes the captured infoframes into the file along with any custom HDR infoframe you have defined, which is what to attach when you ask for help.

All glossary terms