Kirk McElhearn, digging into ProRAW:

One of the key elements of raw files is that they are not demosaiced.

Demosaiced? That’s a new term for me.

From the Demosaicing Wikipedia page:

A digital image process used to reconstruct a full color image from the incomplete color samples output from an image sensor overlaid with a color filter array (CFA). It is also known as CFA interpolation or color reconstruction.

Most modern digital cameras acquire images using a single image sensor overlaid with a CFA, so demosaicing is part of the processing pipeline required to render these images into a viewable format.

Many modern digital cameras can save images in a raw format allowing the user to demosaic them using software, rather than using the camera’s built-in firmware.

OK, got it, back to Kirk:

When you open a raw file in an editing, your software processes the file, performing the demosaicing, along with some other processing, and then allows you to then proceed with other edits. Because of this, there are a number of photo editing apps that perform this demosaicing in slightly different ways; photographers choose the app they prefer according to the results (and for other editing capabilities as well).

But Apple’s ProRAW has already done this demosaicing, which means that, well, it’s not a raw file.

This is just the beginning of a long, interesting take on ProRAW. If you are into the camera side of your iPhone, this is definitely worth a read.