Sharpening your Photos using Unsharp Mask
Introduction
This is a basic introduction to sharpening your photographs in Photoshop using Unsharp Mask, which despite its unlikely sounding name, is the sharpening tool of choice for most photographers.
When to Sharpen your Photos
Whether to sharpen your photographs, and by how much depends on whether your shoot your photographs as JPEGs or RAW format.
JPEGs
JPEGs have already been sharpened, colour saturated and had contrast adjustments made by your camera, based on the camera’s internal settings. In producing a JPEG, your camera does much of the photo editing work and then throws away what it regards as unnecessary data in order to compress the file size and present you with your photograph.
Sharpening JPEGs further in Photoshop is mostly unnecessary and can result in over-sharpened images (see How to Sharpen your Photos
below). In some cases, additional sharpening in Photoshop might be possible providing it is done on a very limited basis and with care.
RAW
When your camera is set to capture images in RAW format, your camera produces files (photo files) that are not manipulated by your camera. It captures all the data from the scene and then hands the image over to you to make adjustments to sharpness, colour saturation, contrast and a range of other variables. Because data is captured in its RAW state and is uncompressed, file sizes are much larger than JPEG files.
With RAW files you are in charge of producing the final image, not your camera’s internal settings. As a consequence, you have much more scope to sharpen your RAW images, and make other adjustments using Photoshop.
When Sharpening Won’t Help
Sharpening will not, magically, put out-of-focus photos back into focus, and it won’t make blurred images sharp. It may help give the illusion of improved focus by adding contrast, but that’s all.
It’s essential to capture as good an image as possible ‘in camera’. That means taking care to focus correctly and avoid camera shake. Use a suitably high shutter speed when hand-holding your camera and a tripod/cable release with slow shutter speeds. After taking your photo, zoom in using your camera’s preview screen to check that your image is sharp.
Effects of Over-sharpening
Over-sharpening makes your photos look ugly. Unsightly halos appear along edges and dark edges become hard and jagged, pixels become blocked together, losing detail, and other pixels may change colour completely. Over-sharpening also makes any digital noise more prominent.
(Digital noise are random coloured pixels, sometimes seen in shadow and sky areas – more prevalent when shooting at high ISOs.)
How Unsharp Mask works
Unsharp Mask works by enhancing the appearance of detail in an image. It does this by adding tiny increases in contrast at object boundaries. These are known as sharpening halos. This added contrast results in sharp transitions and detail with clearly defined borders, making the image look sharper overall.
Why is it called Unsharp Mask?
The term Unsharp Mask is a throw back to the days of print processing, when edges of images where masked during processing, to make them look more defined, resulting in photographs which looked sharper.
Where to find Unsharp Mask in Photoshop
In Photoshop or Photoshop Elements, (depending on which version you are using), you’ll find Unsharp Mask under the Filter, Sharpen or Enhance drop down boxes, at the top of your Photoshop screen.
Important: Do sharpening Last
It is important to do any sharpening as a last step in editing/enhancing your images. This is because any subsequent adjustments can undo or damage your sharpening.
How to use Unsharp Mask
You will need to have a photo displayed in Photoshop before using the command (sorry if this sounds obvious). Clicking on Unsharp Mask brings up a smaller dialogue box and a mini preview area. The preview area displays a 100% view of your image. You can change the previewed are by clicking on different parts of your main image. I try to find an area on the main image with edges, which I can use to gauge the effects of sharpening.
The dialogue box has three sliders for Amount, Radius and Threshold. You can adjust these by using the sliders or entering a value directly into the boxes above them. (This is discussed below.)
You can test the effect of the changes you make by placing your cursor over the mini preview pane and left clicking with your mouse. This shows a zoomed in portion of the image at 100%, which displays before and after views of the sharpening effect.
If you want to view another portion of your photograph in the mini preview pane, move your cursor back over your main image and left click with your mouse.
About the Unsharp Mask controls
Amount
The Amount setting allows you to adjust the intensity of the sharpening i.e. higher values result in higher contrast along edges. (Settings range from 1 to 500%.)
A good starting point when sharpening RAW images is 100%.
Radius
Radius controls the width (from 0.1 to 250 pixels) of the sharpening halos. Low radius settings produce narrow sharpening halos, higher settings produce wider ones.
The value you use depends on the type of image that you are editing and its resolution. Images with lots of narrow edges and fine detail require a slightly lower radius setting than images with wide edges and less detail.
Additionally, low resolution images require smaller radius values than high resolution images.
A setting of 1 is a good place to start.
Threshold
Threshold specifies how much difference in brightness must be present in adjacent pixels before any sharpening is applied. (Settings range from 0 to 255) Low values apply the sharpening to edges with very little contrast. Higher values sharpen only when pixel contrast is higher.
The Threshold setting lets you protect skin tones and slightly noisy skies from being sharpened. Beware: Increasing the value too high can cause unnatural transitions between sharpened and unsharpened areas.
A good starting value is 1.
Let your Eyes Guide You
Look at the preview panel. If you start seeing unsightly halos, colour shifts or digital noise appearing in your image, reduce the sharpening amounts. Bear in mind that images which look slightly over-sharpened often print well, so it pays to experiment.
Here are some Unsharp Mask ‘recipes’, which you can use as a starting point for sharpening different types of images.
Some suggested Unsharp Mask Settings*
For people:
Amount 150%, Radius 1, Threshold 10
For cityscapes, urban photography, or travel:
Amount 65%, Radius 3, Threshold 2
For general everyday use:
Amount 85%, Radius 1, Threshold 4
*Courtesy of Scott Kelby’s book: The Digital Photography Book Vol. 1. How to Make your Photos Look like the Pros’
Article © Mark Elliott www.better-photos.co.uk
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For more interesting people pictures. Use the rule of thirds for people, too. Don’t place people dead centre in the frame – move them to one side. To keep them in sharp focus, point your camera at them, half-press your shutter (you should hear the auto focusing bleep). Keeping your shutter half-pressed, you can now recompose your picture and press the shutter fully to take the shot.
