Lightzone - free, open source alternative to Lightroom

Lightzone is free, open source, software for editing photos. It is similar to Adobe Lightroom. You do have to create a free account on their site, but it is quick and easy. 

Lightzone is available for Windows, Mac, and Linuz. You can edit batches of photos with effects and styles, color masks, and more. It can make it appear as if you took the photo under different lighting conditions, clean up photos and more. 

There are help videos and forums on the site with an active community to help you use it. 

This is a great alternative for schools and students.

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