There are many problems that can affect the visual quality of an image. Problems that can show up in images include the following:





Why do these problem show up in images? If you are like me, sometimes you just want to point-and-shoot. I don't always fuss with camera settings--or sometimes I just forget a critical camera setting.

For instance, overexposure can usually be avoided by setting the camera to underexpose images by -1/3 to -1 stop: if this is done, detail in bright highlights are not likely to be lost. The camera's exposure compensation is adjusted to do this. Do I always do this? Nope! That's one reason I need a program like Photoshop to correct image defects like that shown in Figure 4.

Unfortunately, once highlight detail exceeds the dynamic range of the camera, the detail is lost forever. What can be done in this situation? In Figure 4, we can copy appropriate sky background from another image and replace the blown-out sky. Pasting in replacement background is also a good corrective solution for the flash reflection shown in Figure 7. 123di has tutorials on correcting highlight problems.

Many times, my photos must capture detail in both very bright areas and deep shadows at the same time. These high-dynamic-range (HDR) images take special processing. 123di covers this topic in detail.

As explained in 123di, the best solution to this problem is to "exposure-bracket" a subject and then combine them in the "pixel room". Modern digital cameras can often be set to automatically bracket a subject.

If you didn't take such a series of images, and if you took the original image in the "raw" format (covered extensively in 123di), the "bracketing" can be simulated in the "pixel room" using a technique called "Luminance Masking."

Luminance Masking can tame a high contrast scene and help reduce loss of highlight and shadow detail. This technique works with images saved as RAW images. Briefly, the technique is analogous to taking two images: one image is exposed for the highlights and another for the shadows. The images are then combined in the digital darkroom to take advantage of the best of both.

The two images below show what can be accomplished using the Luminance Masking technique. The first image is the original "raw" image. I underexposed this original image in order to preserve the highlight detail. The second image shows the final image after Luminance Masking. Other techniques were used to correct camera wide-angle distortion (lens distortion is a 123di topic).



After processing, detail both outside the entrance — including the rosy light reflected in the ceiling — and the interior details show clearly. 123di thoroughly covers the topic of image combining.

It should be noted that several problems might have to be corrected in any given image. Many techniques are sometimes required to bring out the best in an image. I confess, I haven't taken the *perfect* image yet; but since I am not a photo-journalist, I don't have to deliver my digital images untouched by processing. I can utilize any of the techniques discussed in 123di to either make my images look closer to the scene as I saw it or just to make a beautiful picture.

I do alter my images in this way, when necessary--to make them more closely resemble the scene as I actually experienced it. However, on my web site, I make it clear that I do so.

Perhaps the most valuable content in the 123di manual — for photographers at all levels — are the materials showing how to *avoid* image problems in the first place. This content begins with topics about digital cameras and their sensors and then thoroughly presents processing techniques that not only prevent or overcome problems — but also make the images "pop."