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Friday, October 1, 2004

High-Tech Route To Better Image Quality


Now you can get more out of all lenses, even making low-priced optics perform like the best


Simply play around with the sliders until the horizon is straight, for example. One thing you must do with this program is be sure your horizon is level before making these corrections. A quick and easy way of straightening a horizon is to use the crop tool to give a basic crop, then bring in a crop edge to the horizon. Rotate the cropped area (put your cursor outside the area and it will turn into a curved cursor for rotation), so that this edge matches the horizon. Then drag the crop edges out to the desired crop for the whole photo and hit enter. (This is shown in the video, Enlightened Photography: Photoshop by Example, available at www.rsphotovideos.com.)

LensDoc offers added control, but that comes with a price—more complexity. Still, it's a fairly simple program dedicated to correcting lens problems (although it offers sort-of fun-house distortions you can use for the effect). The program gives you multiple options, starting with the lens. It includes a variety of lenses under the Specific Lens choice, but if it isn't there, you can use the Generic Lens option. Then you can choose to correct distortion for lens issues, plus you can adjust perspective and rotation problems due to the way a subject was shot. You can use a "Less/More" slider to tweak the adjustments the program makes.

The program gets more precise, too. You have the option to set three points on the line needing adjustment (e.g., the horizon) and the program will base its corrections on that. It's so precise that you have to set these points carefully (you can magnify the image as needed). You can do up to two different lines, too. There's a choice between novice and expert modes, but I've found little need for the expert mode (it gives more options, though).

DxO Optics Pro takes an entirely different approach. This is a remarkable program in what it can do, although it's limited to specific lens and digital camera combinations (the other programs mentioned here will work just fine with scanned images, too). DO Labs originally created a refined optical evaluation program. This gave optical testing new capabilities—a lens could be examined in minute detail for everything from distortion to vignetting to chromatic aberration defects to sharpness throughout the image area. It also looked at how lenses interacted with specific digital camera sensors.

Then the company went further and found ways to make corrections to a digital file that would adjust for lens problems. Their engineers examined lens and camera combinations to discover what problems the lenses had, then they created specific corrections for that combination. This allowed for an extremely high degree of correction. While I haven't tried this program with every combination available today, I've seen some great results with even pro lenses. Any uneven light and variations in resolution are corrected. Chromatic aberration is eliminated. For lower-priced lenses and cameras, the results are nothing short of amazing—these lenses perform as well as far more expensive glass. I've seen a before and after using a Sigma 15mm full-frame fisheye that corrected the image to full-frame rectilinear with superb results.

The program is simple because all the correction work already has been done. Simply choose the image file and tell the program what image corrections you want done, then it does the job quickly. The major limitation of this program is that it only works with specific lens/camera combinations, so if you have something not on the list, the program won't work (it reads the metadata for the image so it knows what's being used). However, you can buy new camera lens modules alone as needed.

Adobe added some lens correction capabilities in the RAW conversion part of Photoshop CS. You have to go to the Advanced part, then click on the Lens tab. There's no correction for lens distortion, but the software corrects for chromatic aberration and vignetting, two common issues for lower-priced lenses, as well as all digital cameras in certain situations. Chromatic aberration creates colored fringing along the edges of hard contrasts at the outer parts of a photo—this will weaken the sharpness and crispness of an image. Vignetting is simply the slight darkening of the edges of the photo. Edge darkening in the computer is an important tool because you can control how much and where it appears. Vignetting isn't desirable because you can't control it at all.

Using the RAW conversion Lens tools is easy—they're all based on sliders. It works best to enlarge the image so you can see details of contrast where chromatic aberration shows up (look to the outside areas of the image). Vignetting adjustments are done when the full image is seen (not enlarged).

These tools can be used in combination—for example, combining a lens distortion plug-in control with chromatic aberration correction. But no matter what you use, these programs promise a new level of image quality possible from any lens and camera.

 


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