Saturday, May 1, 2010

The Lens Correction Filter in Adobe Photoshop CS5

If you take a photograph with a digital camera and load your picture into Photoshop CS5, its lens correction filter can automatically detect the manufacturer, model and lens settings that you had used, using the image file’s EXIF data.

When it doesn't have the additional information needed to correct any changes your camera and settings might introduce, Photoshop CS5 presents a button that lets you search the Web for this information in a trouble-free way. In either case, it automatically corrects lens distortions and fixes chromatic aberration and vignetting.

However, there are other scenarios: In another blog, The North Country Chronicles, I posted the photograph (jpg file) that is shown in the figure below.

This image was created by scanning a century-old picture that had very obvious distortions. Just take a look at the flagpole and the corners of the main building.

So, I spent about 10 seconds to manually straighten the flag pole and corners of the main building by dragging the Vertical Perspective slider in the Lens Correction Filter of Photoshop CS5 a little to the left as shown in the figure below.

{click on image above for a larger view}

and was immediately presented with the compensated – to a visually acceptable level - image shown in the next figure.

This manual intervention was required because no digital photography was available in 1917, when this particular photograph was taken with the Kodak Junior, Model A camera shown below, nor was digital photography used in any of the steps taken in my correcting of this photograph.

Note: The North Country Chronicles post where the original photograph appears is about the early 20th century. So, I chose to leave the original – that is, uncorrected - scanned image there.

The final figure below presents an overview of the flagpole (and other objects) correction process for the case where a digital camera is involved.

While I’m stopping here, I encourage you to watch the following easy-to-understand videos that demonstrate a good deal of additional functionality provided in this extremely handy Photoshop CS5 tool.

Click here for Video 1
Click here for Video 2
Click here for Video 3