Dynamic range
A densely packed sensor can be a recipe for low dynamic range images, but Canon engineers have managed to crack this particular problem and the EOS 550D has a very respectable dynamic range of 12EV. Like all Canon’s recent DSLRs, the EOS 550D has both Highlight Tone Priority (HTP) and Auto Lighting Optimizer (ALO) modes to boost the effective dynamic range of images by darkening the highlights and brightening the shadows respectively.
However, Canon has now decided that using both of these together can be detrimental to image quality, and as with the EOS 7D it is not possible to use HTP and ALO at the same time on the EOS 550D. Although HTP can be useful when highlights need protecting, it works by reducing the exposure and darkening the brightest areas. Consequently, many enthusiast photographers will find it better to reduce the exposure and use the ALO options (Low, Standard, Strong and Disable) to determine the degree of brightening to be applied to the shadows.
