Exposure is not how dark or how light an image looks!

That's just plain weird. You could also say velocity increases with brake pedal application. Or sunburn risk decreases with exposure to sunlight.

While underexposure and overexposure will make an image lighter or darker, to ensure the best possible signal to noise ratio and maximum dynamic range, optimal exposure is about recording as much sensor exposure as possible without blowing any important highlights (or compromising DOF/motion blur etc.) and can easily result in an initially too light or too dark image.

Clearly, this RAW image initially appears too dark, but was it underexposed?

Not if you wanted the highlight detail intact it wasn't...

Sure, but image brightness and exposure should be considered and handled independently, they are not the same thing.

Please see my previous reply. It's the processing, standard or reversal, which determines where density accumulates in an image. It's not weird that we have the option of reversal processing of film which also reverses the effect of exposure increases or decreases.

Fortunately, there is no switch in your car that reverses the function of the accelerator and brake pedal.

What I was saying is weird was your attributing the meaning that you did to your construction in this phrase: "Density increases with exposure". Not the fact that we have reversal and negative films.

No argument here. It's always a balancing act to achieve the desired result or to make the compromises which best represent your intent.

Thanks. I already clarified my intention in an earlier post above: "The implication which was intended is that exposure density is directly related to the amount received (how much or how little) by any type of film."

If you could have used a slower shutter speed and/or wider aperture and still met your dof and motion blur requirements without clipping important highlights, then yes, it is under exposed*. Otherwise no.

To maximise the quality of the raw data, at least with regard to minimising visible noise, you need to get as much light as possible onto the sensor while the shutter is open within your dof and blur constraints without clipping important highlights.

* exposure - amount of light striking the sensor per unit area while the shutter is open.

Shot as base ISO to maximize DR, with highlights recorded just below clipping (-4EV, resulting in ISO 200 instead of ISO 3200 with no exposure compromise).

Yes.

I would have left the iso at 3200 and set the final image lightness in post.
For many cameras raising iso for a given exposure* reduces read noise.

By lowering the iso you probably increased the read noise.

It depends on which is more important, read noise or dynamic range.

ISO 3200 would have nuked the highlights (4 stops beyond clipping). This was an extreme scene with ridiculous dynamic range. This was as much a technical ISO invariance exercise as a an attempt to take decent shot. The highlights where recorded just below clipping at base ISO

.Yes, but just a bit,

In this case there was no choice, any increase in ISO would have necessitated a reduction in sensor exposure (which would be worse).

I must say, the old DPR forums were more intuitive to use than here. This will take some getting used to.

This is not true for film, where an examination of the developed film will show whether it was exposed correctly for the development process used.

As noted above, with slide film that uses standardized processing (i.e. E-6), exposure does determine image lightness. However, with some slide films it may be desirable to overexpose the film slightly to get more pleasing colors (lightness).

A vacuum leak in the brake booster will result in the brake pedal causing the engine to accelerate. Ask me how I know.

Ok, it wasn't clear to me if iso 3200 was actually set or not. I assumed it was.

I have never used film so I wouldn't know.

From your reply I assume you agree what I posted is true for digital.

I'm glad you're still around to relate that to us!

I generally shoot with Auto-ISO with exposure compensation, had I not dialed it way back, the ISO would have been at 3200 and the highlights would be toast.

I also prefer Auto ISO as described in my "Why are my photos noisy?" thread on this forum.

Anyway, earlier you asked if your posted raw file was under exposed.

I replied under what circumstances I would see it as under exposed* or not.

* exposure - amount of light striking the sensor per unit area while the shutter is open.

For the same processing, I expose differently for optical print and for scanning. The factor here is what I'm going to do with the film.