Oh, what is raw?

There is no single definition of what raw is. Some would say it is electric charge, some would say it is direct pixel output, some would say it is ADC output, etc., while some - that it is what the camera manufacturer says it is.

Here we mostly deal with the raw that comes in the form of raw files, so for the moment let's consider only those raw files.

Adobe are suggesting the following: "RAW files contain uncompressed and unprocessed image data", but what is image data? Is normalization (artificial black level, ISO, white balance pre-conditioning, noise reduction, etc) allowed here and isn't considered processing? Is lossless compression considered no compression? Are files recorded in a lossy compressed mode are raw in name only?

Consider what Nikon are saying: "RAW image files ... contain all the image information captured by the camera's sensor, along with the image's metadata (the camera's identification and its settings, the lens used and other information). The NEF file is written to the memory card in either an uncompressed or 'lossless' compressed form." OK, how are we supposed to understand 'lossless' here? What is "image information", and what is not?

On a more serious and practical note, IMHO what is important for a shooter is the relation between "photo-" (light) and "-graph" (record, raw data).

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Some prefer craw ;)

A generous interpretation would be a file in which the image data is undemosaiced— is that a word? — and the spectral response of each pixel is the same as that of the hardware.

By the time we can actually view the raw file , is it actually raw anymore as there is a lot going on to convert this raw data into a viewable image . Depending on what raw viewer we use the results can be very different . Given the behind the scenes "cooking" going on , raw is a matter of opinion 😀

Some care may be in order. Lossy vs. lossless, bit depth reduction in certain shooting modes, Bayer vs. YCC with baked-in white balance, and other tricks and "secrets" that affect the latitude

They made it a matter of opinion by avoiding to have even guidelines, not to mention a standard.

I say "undemosaicked" ;)

You can look at the raw image data in a file directly. It is a checkerboard looking monochrome image.

Yep, here's what NEF raw data looks like crammed into a display:

You can consider this to be grayscale-mapped light measurements through a bandpass mosaic, further mapped to their lens-resolved position in a scene. Disregarding camera-cooking... 😆

The histogram effectively shows the 14-bit range from the camera mapped into the 16-bit integer containers of the computer. Bottom-right, 'CMSprof-error (-)' indicates that there is no color management going on, so the image data is being displayed in its 8-bit equivalents on my display.

This is a 500% zoom to the brightest part of the image, so we'd have something to see. The white region is blown pixels, of a locomotive headlight doing its thing. There is actually some gradation in there, hard to tell as the R, G, and B values are so close.

Headlamp looks familiar ...

Here's a Foveon raw composite, no transformation, auto-brightened, 2.2 gamma - courtesy of the excellent RawDigger.

When you see the starting point it is little wonder you can get such diverse results from various raw convertors

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In layman's terms I would describe raw as the dataset the camera optionally uses, according to its settings, to output a jpeg image file.

if you want to look at a raw data you will need a logic probe with led's 😁if you want to hear a raw data you will need a tone logic probe.🤔
academic-accelerator.com/encyclopedia/logic-probe
and a very powerful microscope😜

If you want to get pedantic about it, the "raw data" would be the numbers reported by the ADUs, corresponding to the measurements taken at each sensor location. Displaying it in a raw processor is simply assigning a gray level to each number, which can be considered an alternate depiction of a value. That it's also mapped to the scene is a bit of a bonus. The point is, it's not processed into any summation, distillation, or other departure from the original numbers.

Thing is, I've found it very useful to regard it in its image context. Lets you know the starting point for whatever needs to be done to make a regard-able image.

If you map out bad pixels is it still raw? If you do CDS, is it still raw? If you interpolate over PDAF pixels is it still raw? If it’s losslessly compressed, is it still raw? Why about lossy compression? Or black frame subtraction? Or white balance calibration? Or the kind of fancy calibration that Hasselblad does?