Tuesday, January 11, 2011

Advanced Lens Correction in Lightroom

Last week we started to review the Lens Correction Panel in Adobe Lightroom 3.  Most of the time, simply clicking the option to "Enable Profile Corrections" is enough to counter any lens distortion in your image.  On occasion, you may need to work a little harder so this week we'll look at the "Manual" options to help you get the most control possible in your assault on lens issues.

This is an image I took in the predawn hours of the Cana Island Lighthouse in Wisconsin's Door County Peninsula.  It was taken with the old model of the Nikon 18-200mm lens (one I rented) and shot at 18mm.  If you refer to the lighthouse against the edge of the frame, things aren't looking too bad... until you look at the horizon line and see that Lake Michigan is running uphill.

This screen capture shows I've selected the "Enable Profile Correction" option.  While it's attempted to correct for the barrel distortion, you can see the horizon still angles up to the right.  By positioning your mouse over the Distortion slider in the Lens Correction Panel, the grid overlay will appear over your image which makes it very easy to identify the horizon issue.

At this point, I could select the Crop option from under the histogram (or press the "R" key) and then use the Angle tool to mark the horizon line to straighten the image.  As we're talking about the Lens Correction Panel, however, let's look at an alternate method.

Click the "Manual" option from within the Lens Correction Panel to display a new series of Transform, Lens Vignetting and Chromatic Aberration sliders.  Both the Lens Vignetting and Chromatic Aberration sliders work pretty much as we discussed in last week's post, but provide you with some additional control.  For this image, we're going to focus on the Transform sliders.  Here's a brief description of their functions:
  • Distortion - Just like the slider in the Profile options, the Distortion slider attempts to correct barrel and pin cushion (bend, bulge) issues in your image.
  • Vertical - Imagine that a fixed axis runs through the horizontal center of your image.  Moving the slider left or right will vertically pivot your image on that axis.
  • Horizontal - This time that imaginary axis runs vertically through the center of your image.  Moving this slider pivots your image on that axis.
  • Rotate - Does exactly what it says.  This slider will turn your image left or right from a fixed point in the center of your image.
  • Scale - Drag the slider to the right to "blow up" your image or to the left to "shrink" it.
  • Constrain Crop - With this box checked, your image will automatically be cropped based on the selections of the other sliders to prevent uneven or warped edges.
Alright, let's get back to the lighthouse.  As we've already noted, we have a pretty obvious horizon issue.  Rather than jump right to the "Rotate" slider, let's try a less obvious option with the "Horizontal" slider.

As you can see from the screenshot, I've pushed the Horizontal slider out to the right which causes the image to "pivot" on that imaginary vertical axis running through the middle of the image.  If we compare the horizon line to the overlaying grid, you'll see that we're much closer to having a straight image.  The problem though is that when I select the "Constrain Crop" option, I'm going to lose a sizable portion of my image - everything in dark grey will be cropped at my original aspect ratio.  Let's attempt to fix this from another direction.  "Double-click" on the "Transform" label to reposition all of the Transform sliders to their default positions.

This time I pushed the "Rotate" slider a little to the right and you can see my horizon line has been corrected.  There's much less image loss (very little dark grey showing in bottom left), but the whole image was rotated... including the lighthouse which was originally pretty straight but now leans to the right.  Now what?  Rotate left to fix the lighthouse and we'll break the horizon line in the process.

By bringing the top of the image toward me using that imaginary horizontal center axis, I'm able keep my horizon line straight and adjust the angle of the lighthouse at the same time.  In addition to adjusting the Vertical slider to -6, I've also checked the "Constrain Crop" this time to show the final results of the transformations.

If you've never had the pleasure of trying to correct lens distortion prior to the introduction of these new tools within Adobe Lightroom 3, consider yourself lucky.  With a little experimentation and a handful of sliders, Lightroom can once again save an image otherwise destine for the Recycle Bin.

Do you have any images in your catalog that suffer from lens distortion?  If so, give these tips a try and let me know how things turn out.

Until next time, keep click'n.


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