Auto Lighting Optimizer (ALO) is designed to automatically enhance contrast and exposure of photos and video captured with EOS cameras. ALO is active by default, and is applied to JPEG images and the LCD preview of RAW images.
What is Auto Lighting Optimizer (ALO)?
EOS cameras since the 2007 have included the Auto Lighting Optimizer feature. When the camera is used in fully automatic mode, creative auto mode or one of the scene modes ALO is always used. If program, aperture priority, shutter priority or manual mode is used then a custom function determines if ALO is used and the strength of the enhancement.
ALO is designed to deal with four main conditions:
- Underexposed pictures taken with automatic exposure
- Low contrast scenes
- Underexposed flash scenes
- Backlit exposures
ALO is designed to help photographers get pictures with enhanced contrast and exposure in less than ideal situations.
Manual mode and ALO – check the details for your camera
ALO is active at the standard setting by default for Av, Tv, P modes. ALO used to be automatically disabled when shooting in manual exposure mode and could not be activated. The EOS 5D Mark II is one camera that exhibits this behaviour. In the recent generation of cameras it is possible to have ALO active even in manual exposure mode.
If you use highlight tone priority or high dynamic range modes on the camera auto lighting optimizer will be disabled automatically.
RAW images and ALO
I often hear photographers say they shoot RAW and therefore it doesn’t matter what the ALO setting is, and certainly it is possible to change or disable the ALO setting in the Canon DPP software when processing RAW images.
ALO affects LCD preview of RAW images
Several of the most recent cameras can process RAW images to produce JPEG images directly from the camera. ALO can be set to Off, Standard, Low and High for in-camera RAW image processing.
Auto Lighting Optimizer example pictures
Since ALO is designed to work enhance flash exposures that may, in the camera’s mind, be underexposed I processed this flash lit picture of Lauren-Christina with DPP to show the results of ALO. As you can see the results are all clearly different. If I had the ALO turned off on the camera then I may have thought the picture was underexposed and incorrectly increased my flash exposure.
Remember the LCD preview and histogram depend on the ALO settings when the picture was taken.
You may also find the Canon Professional Network info bank article on ALO an interesting read.
Optimizer / Optimiser
ALO is an abbreviation for Auto Lighting Optimizer, of course this is an American spelling so in the UK it is sometimes seen written as Auto Lighting Optimiser.