This feature is hidden behind the WITH_EXPERIMENTAL_GAIN_MAP compile flag.

    See https://helpx.adobe.com/camera-raw/using/gain-map.html for an introduction
    to gain maps. Note that in this change, gain maps are not stored as auxiliary
    items as proposed by Adobe, but as a hidden input to a new 'tmap' (tone mapped)
    derived item.

    An 'altr' (alternatives group) box is also added to tell the decoder that it
    may show the tone mapped image (preferrably) or the base image as a fall back.
    The primary item id still points to the base image for backward compatibility.

    This feature is hidden behind the WITH_EXPERIMENTAL_GAIN_MAP compile flag.

    See https://helpx.adobe.com/camera-raw/using/gain-map.html for an introduction
    to gain maps. Note that in this change, gain maps are not stored as auxiliary
    items as proposed by Adobe, but as a hidden input to a new 'tmap' (tone mapped)
    derived item.

    An 'altr' (alternatives group) box is also added to tell the decoder that it
    may show the tone mapped image (preferrably) or the base image as a fall back.
    The primary item id still points to the base image for backward compatibility.

Sync with main branch

Sync with main branch

Add verification code in heif_enc and heif_info