Quote Originally Posted by Johnny Rasmussen
You mentioned you did not shoot with HTP on because of increased shadow noise. Is it really that visible?

It depends on the ISO. HTP works in the context of a constant display brightness and a constant exposure. In that context, low ISO has more noise than high ISO. In other words, when you keep your exposure the same, and the raw conversion is made to come out with the same brightness, higher ISO has less noise (sometimes a lot less) than low ISO. This is the opposite of how we normally think about ISO because we don't normally keep exposure fixed. In essence, it separates ISO-as-a-camera-setting from ISO-as-an-exposure-index.


So ISO 3200+HTP (which is actually just ISO 1600) has the exact same noise as ISO 3200 without HTP, but ISO 200 has less noise than ISO 200+HTP (which is actually just ISO 100).


The way HTP works is pretty simple. Say you shot a scene at ISO 200 f/4 and developed it with default raw converter settings, and it came out with too much blown highlights. Then you shot it at ISO 100 f/4. Now the highlights are better, but the overall image (midtones, shadows, etc.) are too dark. So you push the midtones and shadows without blowing the highlights (e.g. by using a curve). This makes the increased noise of a lower ISO setting visible (you wouldn't see the difference if you left the overal image darker). That is what HTP does.