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Lens Correction

The Lens Correction filter consists of a very user-friendly dialog box which allows a range of related lens corrections to be performed simultaneously.

Barrel Distortion

Barrel and pincushion distortion is usually only noticeable in images shot at extreme wide angle or telephoto and specifically with straight lines close to the edges or in images with an off-center horizon.

One great feature of the Lens Correction filter is that you can drag your pointer over the preview and see the effect of your correction in real time. I found that this, combined with the grid overlay, resulted in quick adjustments that reduce the barrel or pincushion distortion to a visually acceptable level.

Because Photoshop CS2 uses only one correction parameter, compared to three in Panorama Tools, it is less accurate. PTLens, a freeware Photoshop plug-in based on Panorama Tools written by Thomas Niemann, takes away the guessing of the Panorama Tools parameters and currently covers a wide range of lenses and cameras, including many digital compacts with converters.

The thumbnails below link to the full size images. The red squares in the thumbnails indicate where the crops below were taken. The 80 x 80 pixel crops are 2 times (pixel) enlarged via nearest neighbor interpolation. I drew a straight red reference line in the original, the Photoshop CS2, and PTLens results so that it "touched" the straight line of the building in the middle in all three cases (as shown in the second row of crops).

Original
After Photoshop CS2
After PTLens
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Original
The distance between the red reference line and the glass of the building is large in the top and bottom crops.
Photoshop CS2 (setting +5)
The distance between the red reference line and the glass of the building is reduced in all crops but the reduction is not constant.
PTLens
The red reference line is perfectly parallel to the glass of the building from top to bottom.

The above results show the limitation of having only one parameter available in Photoshop CS2. Increasing the correction parameter to more than +5 would further improve the correction in the first and third crops, but would introduce pincushion distortion in the corner areas (there is already a hint of pincushion distortion in the bottom crop).

I'd say that if you want a quick and easy correction that combines other corrections such as straightening horizons, adjusting perspective, vignetting and chromatic aberrations, the Photoshop CS2 Lens Correction filter will lead to visually acceptable results in most cases. However, if you are a perfectionist or are working on a mission critical image, the free PTLens plug-in will provide a higher level of accuracy.

Chromatic Aberration

The chromatic aberration correction provides a reduction that varies more with the image than is the case with Adobe Camera Raw (discussed on the next page), which in many instances eliminates all chromatic aberration. In the first example, the chromatic aberration correction performed nearly as good as in Adobe Camera Raw (if you look at the enlargement, there are some color artifacts around the edges in the lens correction crop). In the second example, the chromatic aberration correction performed less well than Adobe Camera Raw as quite a bit of chromatic aberration remains.

Original with
Chromatic Aberration
After Photoshop CS2
Lens Correction on JPEG
After Photoshop CS2
Camera Raw 3.1 on RAW
Original with
Chromatic Aberration
Chromatic Aberration
virtually eliminated
Chromatic Aberration
completely eliminated
Original with
Chromatic Aberration
Chromatic Aberration
only partially eliminated
Chromatic Aberration
completely eliminated

Vignette

Unlike chromatic aberration correction, the vignette correction performed equally well as in Camera Raw. And unlike the barrel and pincushion distortion, it performed better than PTLens as well. Note that in order to achieve visibly similar results, the vignetting slider adjustments in the Camera Raw window will be different than those in the Lens Correction dialog box.

Original
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Notice the vignetting in the right corner
After Photoshop CS2 Lens Correction
After PTLens
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Vignetting is completely removed
Some vignetting remains
(more visible on full size image)

Transform

The perspective and the angle adjustments are the same as those in the Image -> Transform command. There is also an angle tool to automatically straighten horizons (similar to what you can achieve with the Measure tool). So although this is nothing new, it is very useful to have those adjustments available in one dialog box while doing other lens corrections.

 
This article is written by Vincent Bockaert, author of
The 123 of digital imaging Interactive learning Suite featuring
Adobe Photoshop Elements 2 & 3 and Photoshop 7, CS & CS2
Click here to visit 123di.com
 
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