This is one of those situations where the actual concepts are fairly straightforward, but explaining them can be difficult, and thus understanding them can be a challenge.
The reason why using HTP causes greater noise in the shadow areas is because a key part of the whole HTP "system" is a numerical "boost" of the brightness in the shadow areas when the image is processed. This boost is necessary to make up for the inherent underexposure that we get when capturing while in HTP mode.
First, it's good to understand that the root cause of almost all noise complaints with DSLRs is underexposure followed by "brightening" of the image numerically, in the computer, to compensate for that underexposure.
I think of this the same way as making an audio recording. If you remember making actual tape audio recordings, you'll remember that tape sounded very good, but if you turned up the volume too high, you started to hear a lot of "tape hiss". So if you recorded the signal onto the tape too low, then you'd be forced to turn up the volume very high on playback, and that meant that you'd hear a lot of tape hiss.
Digital camera noise can be a lot like audio noise. If we record "too soft" and have to make up for that by turning up the gain when we play it back, then the noise (that's really always there), gets amplified more, and we see it as noise in the image.
Underexposing is the equivalent of recording too softly. To compensate, we must turn up the gain later, and that reveals the noise that's always present. It just makes it more visible.
So this is why underexposing, and then compensating by turning up the brightness in post processing, makes the noise so bad. In effect, turning up the brightness is what brings out the noise. And underexposure is what makes us need to turn up the brightness.
Ideally, we would not need to do any adjustment of the brightness of an image when we process it. And thus, the noise that is always there would not be objectionable. But if we underexpose, then we must turn up the "gain", and that turns up the "noise" right along with the "signal".
OK, so when we shoot with HTP enabled, the camera is purposely underexposing the entire shot by one stop. Then, the HTP processing that goes along with it turns up the gain by one stop for the shadow and mid-tone areas. The gain is progressively "rolled off" as we get to brighter and brighter areas of the image such that by the time we're at the brightest areas, there is no extra gain at all.
Thus, with HTP mode, we will always have a full stop of extra noise in the shadows of the image to begin with. And any further increasing of the brightness when we process the image will just make it worse.
"Shooting to the right" is a technique used when shooting in RAW mode. It's not really useful for JPG shooting.
You are correct. It means to shoot so that the brightest highlights of interest are just "kissing" the right edge of the histogram. We don't actually have a true RAW histogram, though, so that adds extra complexity, but we'll ignore that for now.
The idea of "shooting to the right" is that we maximize the dynamic range of the capture system by making sure that the brightest areas of interest are recorded at the very top of the possible range of recorded brightness values. That way, we use the full range of the system and don't waste any space at the top end.
Since we're shooting in RAW, it doesn't matter if the image was intended to be a "low key" shot with no bright highlights at all because we can simply turn the brightness down when we process the RAW. Turning the brightness down has no bad effects (unlike turning the brightness up). So in all cases, if we've "shot to the right" correctly, we'll end up with the best possible dynamic range, with best shadow detail and lowest possible noise in the final image.
Shooting to the right optimizes our use of the capture system by fully exploiting its entire range of possible number-to-brightness assignments.
--
Jim H.
