Troubleshooting Photos –
Picture Is Harsh, With Unnatural OutlinesÂ
Problem
The picture is harsh and unreal. The people or objects appear to have black or white lines around them, like the keylines in cartoons or the buttons to the left of the photo. Color may be uneven.
too sharp, the first image, is a photo that has been sharpened very heavily. original shows the photo as it came from the camera with no sharpening in the camera or on the computer. sharpened shows a correctly sharpened version. Compare this with the first version to see how dramatically over-sharpening can spoil a photo.
What should you look for?
Look at the telephone lines in the too sharp version – all have a distinct white halo around them. In fact, every tone change has these halos, but they're most visible in straight lines in areas of consistent color and tone . Look also at the roof lines and the stop sign at right. These halos tell you that the picture has been sharpened, and if they are as prominent as these, that it has been sharpened too much.
Sharpening is a traditional technique that makes tone changes more distinct. Edges are emphasized by modifying the pixels at the edge so that the darker side of the tone change is darker and the light side is lighter. This makes pictures look more in focus; it can even rescue pictures that are a bit out of focus.
Applied with a heavy hand, sharpening makes photos look like cartoons, with heavy keylines around each edge and strange color shifts. Compare the left second-story window of the yellow house in the over-sharpened version with the same window in the original. The fine red line is an artifact introduced by overly aggressive sharpening. Also look at the cladding on the houses in the detail version – the shadow under each board has become black, instead of a darker version of the house-color. The face of each board has turned from a realistic solid color to a color bordered by an exaggerated white edge. Individually, these changes may not seem terrible, but together they degrade the picture so it takes on an unpleasant aspect.
The detail 1 button shows a 200% enlargement of what happens to an over-sharpened image to give it its unnatural appearance. The detail 2 button is a detail of the correctly sharpened version. At 200% it may still look harsh, but note that it has none of the abrupt color changes or unusual colors of the over-sharpened detail.
What should you do?
First, turn off any sharpening in your camera. In-camera sharpening is a permanent change. This causes two problems. First, it's almost impossible to undo seamlessly at a later date if you decide you want less sharpening. Second, when a camera-sharpened image is sharpened again, you're more likely to see artifacts than if you make one pass of the right amount of sharpening.
Virtually all pictures need some sharpening to offset the limitations of your camera, your scanner or your printer. Colors will be brighter, edges better defined and everyone will agree the picture is better. You can even rescue photos that are a bit out of focus. Not all pictures, however, should be sharpened the same amount.
In digital sharpening, you can vary the emphasis (the degree of darkening or lightening that's applied) and the width of the area that is affected. You can also select the degree of tone difference that must be present before sharpening is applied. By learning to use these variables, you can apply sharpening that improves the picture, yet won't make people say, "Oh, that's been sharpened."
The tools in Adobe Photoshop and Photoshop Elements are professional-quality, but stay away from the Sharpen and Sharpen Edges commands – these are the bludgeons used on the over-sharpened picture above. Instead, learn to use Unsharp Masking (USM). Stay away from the Sharpen tool until you're thoroughly familiar with USM. Making significant changes to the sharpness of one area in isolation from the rest of the photo can easily make it look very unrealistic. A global change won't stand out in the same way.
You won't use sharpening the same way on every image.
- Photos that will be viewed from a distance need more pronounced sharpening than photos that will be seen close up (remember this if someone asks you to do a billboard).
- Use more sharpening on images in which viewers expect well defined edges, such as machines, jewelry or modern buildings.
- Use less sharpening on soft-edged subjects such as people or soft furnishings. Be very careful sharpening faces in close-up, because sharpening emphasizes wrinkles, acne scars and other skin defects that people won't thank you for showing.
- Photos that have been shot at a low quality setting or that have already been re-saved as JPEGs will need careful handling and some experimentation with the sharpening settings to avoid emphasizing JPEG artifacts (also see this example). Try increasing the Threshold setting to increase the tone difference required before sharpening occurs.
How do you fix it?
Photoshop and Photoshop Elements' Unsharp Masking (USM) filter provides three settings for fine-tuning your sharpening:
- Amount sets the level of difference by which the light side of an edge is lightened and the dark side is darkened. 50% to 100% makes a slightly more distinct edge. 500% looks like everything is outlined in black ink,
- Radius sets the width of the sharpened area in pixels.
- Threshold determines how different an edge must be from its neighbor before it is sharpened. '0' emphasizes every difference (which creates strange artifacts) while at '255', almost nothing changes.
How much of each to use in real life? A respected writer suggests a fun way to familiarize yourself with the settings in the USM dialog. Open any picture then set sharpening values of:
- Amount: 500%,
- Radius: 2.0 ;
- Threshold: 0.
This will sharpen every pixel by an outrageous amount, so plain walls will sparkle with strange colors. Reduce Threshold until the noise (the sparkling) goes away, then play with Amount until the picture looks good.
As an example, the 'sharpened' version of the four houses was done with USM set at:
- Amount: 87%;
- Radius: 1.0; and
- Threshold: 15.
An equally pleasing copy was printed at about 3.75 in. / 9 cm high with a Radius of 2.0. The greater Radius is needed in print because a pixel on screen is displayed at 1/72" or 1/96" whereas when printed, picture information is translated into a printed dot of between 1/200" and 1/300". Therefore you need a higher value to make a distinctly sharpened edge. Pictures that are viewed at a distance can tolerate – and often need – more aggressive sharpening to offset the effects of distance. Look closely at a poster or a billboard and you will see the heavy sharpening that spoils a normal-size photo. At long viewing distances, heavy sharpening is needed to have any impact.
In the USM dialog, use the magnified view in the dialog box alongside a normal-sized preview to ensure you finish with a pleasing level of sharpening with no unpleasant artifacts. Checking then unchecking the Preview checkbox gives you a quick A/B comparison to judge the effect.
