PIX 2015
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Lens and perspective corrections in Lightroom 3

Up to now, lens corrections in Lightroom and Photoshop has meant manually manipulating various sliders to reduce the amount of visible distortion, CA and vignetting in particular photographs. These options are still available in Lightroom 3 but new functionality has been added, including perspective correction and lens correction profiles.

Perspective Corrections

The new 'transform' options introduce to Lightroom a combination of adjustments that are designed to enable quite extreme alterations to a photograph's geometry. Similar adjustments have been possible in Photoshop for a while, but this is the first time that Lightroom has offered these controls. Using the 'transform' sliders in the 'Manual' tab of the lens corrections dialog essentially allows you to mimic the sort of control over perspective that you would get from a tilt-shift optic.

Original image
After correction using transformation tools

Lens Correction Profiles

Previous versions of Lightroom featured the standard sliders for distortion, CA and vignetting, and these are still available in Lightroom 3, but the new software goes one better, and also includes lens profiles.

Lens profiling is far more versatile, especially when it comes to correcting distortion, which is rarely as straightforward as the mathematically simple barrel/pincushion pattern described in the slider controls. In theory, by precisely recording a lens's various imperfections at a range of focal lengths and focusing distances, it is possible to create a profile which corrects these problems from images taken with that lens. Naturally, even the best profile can't make a poor lens into a perfect optic, but we've seen for ourselves that a good profile can make a lot of difference to images shot with fairly unremarkable glassware.

The range of profiles built into Lightroom 3 isn't huge at present, and of the DSLR manufacturers, only Canon and Nikon are currently represented, but if you've got a collection of Sigma lenses you will find yourself very well served.

Adobe and Sigma worked together on the Japanese lens giant's profiles, which can be applied either manually or automatically, to individual or batched images. A neat aspect to Adobe's lens correction profiles is that everything can be fine-tuned. If you want to adjust the amount of distortion, CA or vignetting correction that a particular profile is set to apply, you can. Your adjustments can then be saved for the profile.

Canon EF-S 15-85mm f3.5-5.6 IS USM

Canon's 15-85mm for APS-C DSLRs doesn't quite qualify as a superzoom, but it is a step up from Canon's kit options and as a carry-everywhere lens its primary appeal is versatility. Optically, the 15-85mm isn't a match for Canon's more expensive L-series lenses, but it isn't bad. The main issues are distortion and chromatic aberration, which is very noticeable towards the corners of images taken at the wide end of the zoom.

Canon 15-85mm uncorrected
Canon 15-85mm corrected (using Adobe profile)
Canon 15-85mm corrected (using DPP profile)

Here we can see that Adobe's lens correction profile has done a very good job of removing the distortion and if you take a look at the full-size original files you'll see that CA has been fixed too, but we'd hesitate to say that Lightroom 3 did a better job of correcting this image than Canon's Digital Photo Professional, when lens corrections are enabled. In terms of distortion and CA correction, DPP does equally well, as we'd expect.

The only differences are slightly softer output from DPP at default settings, and a slightly smaller output size. Whereas Adobe's lens correction profile produces a final image that is faithful to the pixel dimensions of the original, DPP actually creates a slightly smaller file. The difference is small though - 5118x3412px compared to 5184x3456px.

The major benefit of Adobe's lens correction profiles in this example is that they work for JPEG files as well as RAW. Digital Photo Professional's lens correction option is only available for .CR2 RAW files.

Nikon AF-S VR 18-200mm f3.5-5.6G IF-ED

The Nikon AF-S VR 18-200mm f3.5-5.6G IF-ED covers a range equivalent to 27-300mm in full-frame terms, meaning that this lens falls into the 'superzoom' category. As such, it isn't the best lens we've ever tested by any means, and displays heavy barrel distortion at the wide end of its zoom range, shifting to heavy pincushioning at around 50mm, which improves without disappearing towards 200mm.

As you can see from this JPEG example, the distortion at 18mm is complex. Watch the line of the top of the building in this shot, and notice how it describes a wavy line, like a flattened 'w'. This sort of distortion is impossible to fully correct using Adobe's standard 'pincushion/barrel' distortion slider, because it contains elements of both types.

Nikon 18-200mm (JPEG) uncorrected
Nikon 18-200mm (JPEG) corrected (using lens correction profile)
Nikon 18-200mm (JPEG) corrected manually using pincushion/barrel distortion slider in Photoshop CS5

Adobe's lens correction profile has done an excellent job here in terms of distortion correction, although interestingly, CA is much worse in the 'corrected' image. After some head-scratching we figured out why this is happening. Many Nikon DSLRs, including the D300 on which this JPEG image was taken, automatically remove CA in JPEG files. Adobe has confirmed that this lens correction profile was created using files that were converted from RAW images. So, what the profile is trying to do here is remove the known amount of CA it expects to encounter. Only in this instance the JPEG has already had the CA removed (in-camera) so Lightroom's corrections end up actually creating fringing.

This can be inferred from what we found when the 18-200mm was tested - that in this area of images shot at this focal length, red fringing appears on the left of scene elements, and green to the right. This 'corrected' image shows the opposite red-green orientation.

This doesn't mean that you can't adjust Nikon JPEG files using Adobe's lens correction profiles, but it is something to be aware of. CA can of course be easily removed using either the CA slider or the 'Defringe' dropdown options, and if you're a dedicated JPEG shooter you can save this adjustment to the lens correction profile.

Sigma DG 10-20mm f4.5-5.6 EX HSM

When we tested the Sigma 10-20mm f4.5-5.6 EX HSM we noticed strong, and slightly unusual distortion. Although the central portion of the frame (which you can visualize as a rectangle occupying roughly 2/3 of the image area) is more or less free from distortion, things go very wobbly very suddenly at the edges.

Sigma 10-20mm uncorrected
Sigma 10-20mm corrected (using Adobe correction profile)
Sigma 10-20mm corrected (using DXO correction profile)

With the exception of what looks like an aberrant result in the lower left corner of this image, taken at 14mm (where barrel distortion turns into heavy, but very localized pincushioning) Lightroom 3's lens correction profile does an excellent job of ironing this lens out. It is worth noting that this is the only image that we shot which displays this odd asymmetrical distortion, suggesting an isolated glitch with the profile for this particular focal length.

DXO Optics Pro 5 has done a better job though, and if you take a a look at the full size original files (just click on the small versions) you'll see that it has also improved corner sharpness and erased all trace of CA. The downside to DXO, of course, is that quite apart from its expense and (arguably) less than intuitive interface, its profiles are camera and lens specific, and you cannot create your own. Depending on what combination of camera/s and lens/es you own, you may be waiting for a while for DXO to produce a module.

In summary, if you own one of the lenses represented in the built-in profile library, you should find that applying the profile makes a real difference. Our experience is generally positive. There is no doubt that with the lenses that we tried, distortion, vignetting and chromatic aberrations are reduced, but as always, your mileage may vary. Purely in terms of the effectiveness of its corrections, in its current form, Adobe's lens correction profiles are no substitute for a the hundreds of lens/camera combinations profiled in DXO Optics Pro. However, if you own one of the lenses that Adobe has profiled, applying the corrections is very quick, and very easy, which is a powerful selling point.

Please note that we intend to make Adobe's lens correction profiles the subject of a separate article in the near future.

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Total comments: 3

So the three computers had 3 gigabits, 5 gigabits, and 8 gigabits of RAM did they?

Maybe try using gigabytes (GB) and everything will run faster...


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mody hector20

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Total comments: 3