Some time ago, I published
an introductory blog post about Protune. In it, I explained that GoPro uses an S-shaped tonal curve for encoding the image the camera sensor sees into the three primary color channels RGB. The idea here is to extend the range at the far ends at the expense of the intermediate tonal range, in a way that Protune stays within the allowed tonal value range of 8 bits per channel H.264 video data. A good idea, it seems ... but unfortunately not always under water...
