Thursday, March 1, 2012

Adobe Photoshop Lightroom Tutorial - Part XVIII - Tools - Effective Cropping, Straightening and Leveling

Part I - Index and Introduction
Part XIX - Graduated Filters

Lightroom provides some powerful yet easy to use tools that can be used during the development process to retouch, correct and improve your pictures. The tools can be accessed in the Develop module using either the Tools menu or the tool strip, found just below the image histogram and shown in the following screenshot:

Develop Module - Tool Strip

The available tools in Lightroom 3 are:
  • The crop tool.
  • The spot removal tool.
  • The red eye correction tool.
  • The graduated filter.
  • The adjustment brush.

Crop Tool

Cropping is one of the most basic photographic adjustments ever performed: you remove parts of your image and reframe it. You may need to reframe it for a variety of reasons: it wasn't possible to do it on camera, you need to correct an error, or simply you need to change the image aspect ratio.

Although being a task frequently performed, many people fail to realize the real power and versatility of the cropping tool provided by Adobe Lightroom: that's why I'm dedicating an entire part of this Lightroom tutorial to cropping, straightening and leveling an image frame.

To open the crop tool, you can use one of the following ways:
  • The Tools/Crop menu item.
  • The crop tool icon on the tool strip.
  • The 'R' keyboard shortcut.

The crop tool panel can be seen in the following screenshot:

Crop 

The cropping tool in Lightroom, very much alike other cropping tools, can simply be used by dragging the edges of your frame to define the new image frame:

Cropping Tool - Dragging the Frame Edges

Alternatively, you can choose the Crop Frame Tool from the Crop Overlay Panel to replace the existing frame with a newly selected one:

Crop Frame Tool

Just select the tool and click and drag the new frame over the image.

Although quick and intuitive, and suitable in many situations, a completely manually performed crop doesn't guarantee the precision you need in other situations. In case you need to perform a more controlled crop, here's what the cropping tool offers to you:
  • The possibility of specifying and locking the aspect ratio to a chosen value.
  • The possibility of specifying the crop angle either manually or using a leveling tool.

Setting and Locking an Aspect Ratio

To specify the desired aspect ratio of the image frame, you can choose a suitable one from the aspect ratio menu or specifying it manually selecting the Custom item:

Aspect Ratio Menu

If you want to lock the aspect ratio of the crop frame during manual adjustment, just use the lock icon:

Aspect Ratio Lock

Straightening a Frame

Sometimes the image is not leveled and you would like to straighten it. There are three ways to perform this operation:
  • Manually rotating the frame.
  • Manually specifying the angle the frame should be rotated by.
  • Using the leveling tool

To manually rotate the frame, just click and drag outside its boundaries. The mouse pointer will change to a "curved arrow" and you will be able to change the angle by dragging the pointer around the frame.

Manual Frame Rotation

As you can see in the previous screenshot, Lightroom will show a denser frame grid during a manual rotation that you can use as a convenient reference frame to visually tune horizontal or vertical lines.

Alternatively, or as a mean to correct the inclination of the frame, you can change the rotation angle by specifying a value using the angle slider or by introducing a value into the angle input box:

Angle Selection

Leveling the Frame

The third way to specify the angle of inclination of a frame is using the leveling tool.

Leveling Tool

This tool simulates the behaviour of a physical leveling tool: Lightroom lets you draw a reference line over your picture and  it will change the angle of inclination of the frame so that the leveling line be perfectly horizontal (or vertical, depending on its angle of inclination). This is undoubtedly the more precise way you can level a frame in the cases you need to align it, either horizontally or vertically, with a reference line of your picture.

If you wanted to level the frame so that the cross in the following image be perfectly vertical, you could use the leveling tool and draw a line over the cross, as shown in the following screenshot:

Leveling Tool - Drawing a reference Line

As soon as you release the mouse button, Lightroom will realign the frame so that your reference line is perfectly vertical.

Constrain to Warp

Ligthroom includes a Lens Correction tool that lets you correct lens distortions either using manually or using a lens profile (more on this on a post to come). Depending on the type and amount of lens correction that's been applied, the edges of the frame could get filled up by the artificial grey color that Lightroom uses to indicate the "lack of available information".

Suppose you're correcting a strong barrel distortion by applying an "inverse" (pincushion-like) distortion matrix. As long as image contents are "squeezed" towards the center (keeping the corners fixed), you will lose information around the image edges and you'll end up with a result similar to the following:

Grey Artifacts Around a Lens Corrected Image

Although this situation is not very common, at least with so strong a distortion, Lightroom offers a very convenient option in the crop tool: Constrain To Warp.

Constrain To Warp

When selecting this option, Lightroom will ensure that the resulting image frame will always be inside the warped image, that is, it won't intersect with the grey information-lacking zone. For example, as soon as I select this option, Lightroom will resize and realign my image frame so that it is entirely contained inside the warp zone:

Frame Constrained to Warp


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