New Features in Lightroom 4:
* Highlight and shadow recovery brings out all the detail that your camera captures in dark shadows and bright highlights.
* Photo book creation with easy-to-use elegant templates.
* Location-based organization lets you find and group images by location, assign locations to images, and display data from GPS-enabled cameras.
* White balance brush to refine and adjust white balance in specific areas of your images.
* Additional local editing controls let you adjust noise reduction and remove moiré in targeted areas of your images.
* Extended video support for organizing, viewing, and making adjustments and edits to video clips.
* Easy video publishing lets you edit and share video clips onand Flickr®.
* Soft proofing to preview how an image will look when printed with color-managed printers.
* Email directly from Lightroom using the email account of your choice.

Changes in Adobe Photoshop Lightroom 4.4:

- The crop overlay tool resized incorrectly when used in conjunction with the “Constrain to Crop” checkbox in the Lens Correction panel 
- Background graphics were not correctly rendered within the Book Module
- Reading metadata from file would sometimes result in keyword and and GPS metadata to not save for video files
- Updated the "Missing File Icon" for HiDPI / Retina dispalsy
- The supplied lens profile for the Sony RX-1 did not contain vignette information
- Preview in Develop Module was not updated with the latest adjustments
- Square tile artifacts while painting with brush
- Previews of photos in portrait orientation were blurry when viewed in the filmstrip in the Develop module. (Mac only)
- Image in Book Disappears After Changing Modules
- Error changing modules when in Slideshow with second monitor connected
- Stack badges displayed the wrong count when creating new stack that included a preexisting stack.
- Local Adjustment Effect (Brushed Adjustment) Disappears (temporarily) After Selecting a Pin (Win only)
- Book changes are not saved after switching between modules
- The Filter scrollbar within the Library module was not rendering properly.
- Auto-tone was not working properly when used in conjunction with the Exposure adjustment slider. (Win only) 
- The Black&White button was not creating a History state within the Develop module. (Win only) 
- When switching from image to image, remnants of previous image visible on fringes of new photo. This occurred on Retina screens only. 
- RGB color readouts were specified in the Adobe RGB colorspace rather than the ProPhoto linear colorspace. This occurred when working in Soft Proofing within the Develop module. 
- Horizontal artifacts would occassionally appear in DNG files.
- Adding a page behaved inconsistently in the Book module depending on the method used to add a page.
- The state of the “Remove Chromatic Aberrations” checkbox within the Lens Correction was not persistent between sessions of Lightroom.
- Cannot add contacts from Address Book to email on Mac
- Sliders can no longer be moved on Win by using mouse wheel. Working with Lightroom 4 and Adobe Photoshop Camera

System requirements Windows

* Intel® Pentium® 4 or AMD Athlon® 64 processor
* Microsoft® Windows Vista® with Service Pack 2 or Windows® 7 with Service Pack 1, Windows 8 (64 bit)
* 2GB of RAM
* 1GB of available hard-disk space
* 1024x768 display
* DVD-ROM drive

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Homepage :  
http://www.adobe.com/products/photoshoplightroom/