You take a nice picture of some very interesting scenery. The picture is not overexposed and shows no signs of blown highlights. The colors are very nice although they might be improved a bit with Saturation.
But there is a problem. At the edge of the distant mountains where they meet the sky there is evidence of oversharpening. The edge of the sky has a whitish band and the edge of the mountains has a dark, almost black band. Together they form a very annoying and visible line that certainly is not in the original scene. The digital camera put it in.
Who knows why it happens, is it a solution to the blooming problem common with CCDs in video and still cameras? Is it a routine placed in the programming of the camera to alter the image making an improvement or covering up weaknesses in the image capturing system? Not just common to the Sony Mavica FD91 that we use for our images, the oversharpening problem has been observed in images from other cameras as well. The camera or programming oversharpens edges creating a totally fake look.
In a magnified view of our picture above, we see the oversharpening problem clearly in the mountains. At immediate left is the histogram of the unretouched picture which shows no problems with either highlights or shadows. This picture can be adjusted to produce a very pleasant image. Well, except for the oversharpening.
Note: the top illustration is reduced in resolution to fit this web page. The illustration at left and other detail illustrations in this series are taken from the full resolution size of 1024 x 768. Histograms are taken from the full resolution versions as well.
Using the Rubber Stamp Tool
We will use the rubber stamp tool to eliminate the illusion of the black/white line on the edge of the mountains. The trick is to use the options of Darken and Lighten instead of Normal. When using Normal, whatever color or tone you select (where you place the source) will replace the pixels at the destination regardless of what color or shade they may be.
With Darken, only lighter shades or colors at the destination will be replaced by darker tones from the source. If the destination pixel (any one of them within the brush size) is already darker than the tones from the source, it will be left unchanged. Lighten is the opposite of Darken where darker pixels at the destination will be replaced with lighter pixels from the source.
If you haven't figured it out by now, this process will require that you rubber stamp twice. Once to Darken to the sky to eliminate the white fringe and a second time to lighten the dark edge of the distant mountains.
Darken the Sky
The easier of the two is to darken the sky. Of the two problems (white or black), the white fringe is most noticeable. We simply cannot visually accept a white line that outlines our distant mountains. Furthermore, the problem is similar to print's infamous trapping problem. The white fringe allows more white light to strike our eyes and is therefore be more noticeable. Making the process easier is the advantage that there is a lot of source material nearby in the sky. All you have to do is make sure it is the about the same tone and it can be easily cloned against the mountains.
1. Set the Rubber Stamp Options to Darken.
2. Set the Opacity to 100%. This is important because a setting less than 100% will combine the white fringe and blue sky creating a somewhat lighter color sky.
3. Select a Small fuzzy edge brush. Something about two to three times the size of the white fringe to make sure you can quickly cover it. A smaller brush may be tedious and take too long. A large brush may copy slightly different tones away from the fringe that may be noticeable in the final result. If the sky tones are very even, you can use a larger brush. The more uneven, especially a sky with a lot of clouds, use a smaller brush.
4. Start anywhere you like and select a nearby tone of sky as your source. Avoid picking out any ol' sky, the tone should be about the same as the pixels right next to the white you plan to replace. Since it would not be possible to get those pixels (unless you use a brush size of one pixel!) something a couple of pixels away will do. Any further and there may be a slight shift in colors which will be noticeable In the illustration at left, the source is represented by the "+" and the destination by the circle. Don't worry about the localized shifts in tones such as the yellow-greens, blues or gray pixels. They add to the randomness of your sky making it interesting. Just make sure you aren't copying a cloud to an otherwise clear area!
5. Rubber Stamp the white fringe. Don't worry about hitting the edge of the mountains. Remember that you have your brush set to Darken which means pixels darker than those you are cloning will not be changed. Most, if not all of your mountain pixels are darker than the sky and therefore will not be changed. On the other hand, don't go too far into the mountains because there may be some whitish or light yellow highlights of leaves. We don't want them turned into blue sky! At left, our small sample is partially retouched. Notice that none of the darker pixels of the mountain were altered. Continue retouching following the entire edge of the mountains from one edge of your picture to the other. When you are finished, study the picture carefully. Although there will be no white fringe, the dark fringe on the edge of the mountains remains. In some cases this many not be serious and can be left in. In this example, however, the dark line is too visible and must be removed.
Lighten the Mountain Edge
Sharpening affects both extremes of a contrast break, the lighter side is made still lighter and the darker side is darkened. In a severe oversharpening problem such as this, the light blue sky is rendered almost white. The medium mountain tones are rendered almost total black. We now have to lighten the edge of the mountains returning us to what was perhaps a representation of the original scene.
1. Set the Rubber Stamp Options to Lighten.
2. Set the Opacity to 100%.
3. You should a smaller size brush then you used for rubber stamping the white sky fringe. There is too much detail surrounding your sources and you don't want to pick up something unexpected or replace too much. If the detail of the trees is noticeable, use a very small brush and aim to replace just the black or noticeably dark pixels. You should be suspecting that to retouch the tree side of the oversharpening is going to be more tedious than the sky.
4. Select your source carefully. Unlike the sky where you just have to get about the right color, with the trees you have texture to worry about. Further, there are different types of trees represented by different colors. A green pine tree replacing a yellow fringe would not be considered a successful replacement. It is important to look at the color and texture of the pixels near the black fringe to judge what you are looking for. To complicate matters further, you must find a source that is lighter than the dark fringe line. Not too light and not too dark. In all, your selection of sources should always be changing as you move across the mountain top. Each distant tree requires its own consideration in the selection of source material. Your only advantage is that the image is so distant that minor mistakes will not be noticed. For example, no one is going to see that you placed green oak tree on the fringe of a green pine tree so long as the color is about the same.
5. Rubber stamp the dark fringe. Be careful and work slowly being ever prepared to Undo and select a different source. Unlike the sky, this is going to take a bit longer! Notice, at left, how some attention was given to matching the colors from the trees just below the black fringe.
The finished Picture
The finished and adjusted picture is at left. Curves were adjusted to enhance the contrast and saturation was increased in the sky and water as well as red and yellow in the trees. Green was untouched. If you look carefully, you may see some evidence of oversharpening along the distant shoreline. However, since this may be because of a dark edge to the water we need not adjust it. There is some evidence of oversharpening on the trees in the foreground. But maybe these white pixels aren't actually highlights on the leaves. Therefore we don't have to change them. Not all oversharpening must be retouched out. Study your picture carefully and decide if the oversharpening isn't actually a pleasant sharpening which actually helps the contrast of the picture before jumping ahead with the rubber stamp tool. Finally, if the oversharpening isn't too bad, try and adjust only one side of the contrast, usually the lighter side. This may be enough to hide the problem without all the work.
Time for Another?
In this example we have a different problem. The fringe is not neatly along the edge of a relatively smooth mountain top. Instead, the white oversharpening shows through both tree leaves and branches. Notice the close-up views of the two types of problems. In this case we should attempt to replace the white fringe with a more reasonable sky color. As for the darkening, it really isn't that serious and doesn't stand out as a black line as in the mountains. Here, there are only random cases of excessive darkening which is difficult for the viewer to recognize as a flaw. It is somewhat part of the charm of the image. The white glow, on the other hand, doesn't help the image at all any and should be removed.
1. Use a moderately large brush. This will allow you to cover a larger sky area and move faster. Since none of the sky is all that large, minor changes in the tones will not be readily noticeable A larger brush will cover a larger area and that will make finishing the work faster.
2. Select your sources carefully. First, try and decide which sky color belongs between the leaves or branches. Also, make sure the area is large so that you can move around without hitting other foliage clouds. Be sure and select a source that is in open sky. In this way as you click and move around you have less risk of running into something different as source material.
3. Change your Option to Clone (nonaligned). This means that each time you click to clone, the source will be taken from the exact same place each time. This would not be good for doing average rubber stamp work because you will be picking up the exact same patch of sky again and again. Here we are cloning generic sky and the results will be the same tone of sky all over the place. The viewer won't know the difference! Simply find yourself a nice open patch of sky and Clone (nonaligned) from the same patch. However, as you hold the mouse and drag, the source "+" will move around and might run into some other image if you are not careful. The use of this technique is best when you click and let go rapidly while slowly moving the mouse around. In this way you are cloning short bursts of the very same sky or pixels very close to it.
4. Watch out for the clouds. Notice, in the start picture above, that some of the foliage is in front of clouds. Do not clone blue sky in these areas. Find yourself a nice looking patch of cloud to clone. Do you have to clone clouds? Aren't they white already? Actually, clouds should have a slight shade of gray. If you see a white fringe you need to darken the pixels to match the rest of the cloud density.
5. Go ahead and rubber stamp. Notice the difference between the two problem boxes above and the magnified section of the finished image at left. Notice that the white fringe is not totally removed, most if it is. It is not necessary to remove all traces of the white as the stray white and reduced density sky against the twigs will average out to render a nice sky with branches. The view at left, by the way, is slightly magnified. Compare this with the final retouched and adjust picture below.
Compare the before and after versions carefully looking especially for the white fringe within the trees and branches. No adjustments were made to the darkened component of the oversharpening. There did not seem to be any serious problems, even with the branches. As for the leaves, some darker pixels helped to improve the contrast. At left, some more work could have been done with the branches in front of the clouds. This was rather difficult to do as the correct cloud tones were required. Some whitish holes were left in the middle of the large red oak and that doesn't seem to create a serious problem. Perhaps a slightly darker blue sky source might have been better.
It took several minutes to adjust the sky in this picture. Most of the source material was taken from above the two reddish oak trees in the center. This gave plenty of room to move and swish. With Clone (nonaligned) the same point was cloned. During most of the work, the source was out of view far to the left. With enough clear sky around this proved to be no problem.
Epilogue
Is it all worth it? Sure, the picture is much better without the white fringe. But one does have to wonder why it was there in the first place. Do better cameras produce less fringe or maybe even none at all? This certainly would be a point to consider when selecting a digital camera. If, however, the fringe does not bother you, than don't give all this potential retouching work another thought. We have noticed that when the resolution is reduced that the fringe is also minimized a bit. Normally, 1024x 768 resolution pictures directly from the camera are reduced to a width of 200-350 for these web pages. This alone can minimize the fringe to a point where it may not be a serious problem. On the other hand, reducing the image requires a sharpening to crisp the details returning them to their original clarity. The sharpening process returns or accentuates the fringe a bit.
Whatever your choice, the techniques used above can minimize the oversharpened fringes found on trees, buildings and other subjects. These can be quite annoying and certainly not a part of the original scene as it was photographed or as it appears in nature. Whatever the cause of the problem, be it this particular camera or digital cameras in general, consideration must be given as to whether the fringe should be a part of the finished picture.
