Highlight Tone Priority
When initially reading about highlight tone priority, it sounded like the best thing since sliced bread. Not in my experience. Don’t get me wrong, some photographers praise the feature and keep it enabled. I do not.
Purpose of Highlight Tone Priority
The purpose of HTP is to minimize blown (washed out) highlights when taking photos in brightly lit scenes. HTP is said to bring out more detail and dynamic range in highlighted areas. The gradation between grays and highlights become smoother.
But the feature also creates more noise in the shadow areas than if the photo was taken with HTP disabled.
Increased noise and HTP
I take most of my photos in bright, outside light, so I originally turned on HTP to use as a default setting. But after using it for several weeks, I disabled it and prefer to adjust Exposure Compensation instead.
I personally find that increased noise in dark areas of a photo when using HTP is unacceptable. The degree of noise becomes even more apparent when adjusting an image with a tool such as Photoshop’s Shadow/Highlight.
Even the XSi/450D manual warns of increased noise in underexposed areas when HTP is used. I just wasn’t prepared for how much noise there could be. It can be quite strong and undesirable at times.
Increased noise is NOT a reason I bought a DSLR.
Assess a scene before enabling HTP
Before enabling highlight tone priority, I examine the scene. If it contains high contrast areas with strong highlights and deep shadow, I avoid using it. HTP works best for low contrast scenes.
HTP is most useful when photographing scenes such as water, white clouds and snow. Some wedding photographers swear by HTP and use it to bring out detail in white gowns and flowers.
For scenes where the the brightness of lighting changes, such as on a sunny day with lots of clouds in the sky, I stick with Exposure Compensation. Exposue Compensation has a dedicated button on the XSi that is faster to access than wading through the menus to get to the Highlight Tone Priority setting.