SUMMARY
Add a “Highlights/DR” control in EV100 mode that adjusts ISO to capture raw data darker or brighter than the displayed brightness, writing a DNG/HEIF metadata digital gain hint. Works with the requested EV100 Lock feature to separate scene brightness from highlight protection strategy.
RELATIONSHIP TO EV100 LOCK
EV100 Lock: Controls scene brightness and preview brightness (locked throughout)
Highlights/DR: Adjusts ISO offset to capture raw darker/brighter while maintaining same preview
IMPLEMENTATION
ISO Adjustment
Positive highlights value = decrease ISO to capture raw data darker (more headroom)
Negative highlights value = increase ISO to capture raw data brighter (less headroom)
Example: EV100 = 13, Shutter = 1/500s, Highlights = +2
Base ISO for EV100=13 at 1/500s → ISO 200
Highlights +2 divides ISO: 200 / 4 = ISO 50
Raw captured at ISO 50 (darker, 2 stops underexposed)
Preview brightened by 2^2 = 4× to display at EV100=13 brightness
BaselineExposure = +2.0 written to DNG/RAW/HEIF
Metadata
Unsure about exact EXIF/Metatdata fields, but it’s a digtial gain value that tells raw processors to brighten by N stops to match intended EV100. Might be BaselineExposure. This works for sure on Fujifilm cameras with DR100/DR200/DR400 settings.
Preview
Apply 2^highlights_value multiplier to live preview and embedded JPEG. Potentially with an S-curve rolloff on highlights for smoother rendering.
Raw Data
Raw pixels captured at (base_ISO / 2^highlights_value), darker (positive) or brighter (negative) than the EV100 display brightness.
Zebras
Zebras display based on raw data clipping and noise floor. Increasing highlights (lower ISO, darker raw capture) shows fewer highlight zebras as more headroom is preserved, but more shadow/noise zebras as samples are pushed into the noise floor. Decreasing highlights (higher ISO, brighter raw capture) shows more highlight zebras as highlights clip sooner, but fewer shadow/noise zebras as the signal is lifted above the noise floor.
Technical Note
This is similar to Fujifilm DR settings - it shifts the position of mid gray relative to saturation. ISO standard places mid gray 3 stops below max. Highlights +2 uses ISO 50 instead of ISO 200, placing mid gray 5 stops below saturation in the raw file while maintaining the same preview brightness at EV100=13.
One note, the iphone might be obscuring some of this behavior behind it’s ISO setting, it may be a combination of digital and analog gain if the sensor is really ISO invariant.