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Perhaps one of my more popular images. One that I wasn't so happy with personally. I aimed for a little blur, to emphasise how close the Sea Lions came on the dive at Narooma's Montague Island. Unfortunately this one bumped the lens of my Nikonos V, so the blur was a little too much.
Sharpening can't fix this, but in someways, breaking the rules adds to the effect.
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Sharpening Your Images
Almost every image that is captured digitally needs some degree of sharpening. As the subtleties of detail and colour in the world rarely fit into the number of pixels in an image (however captured), information is lost, leading to a general softening of your image.There are various sharpening filters available in applications such as Adobe Photoshop or Adobe Photoshop Elements, including a Sharpen filter, Sharpen More filter, Sharpen Edges filter, and the Unsharp Mask filter. These tools serve to enhance the edges within your images, thus sharpening their appearance.
The first three of these are completely automated, and whilst it may be worth experimenting with them, you have little capacity to alter the effect of sharpening. Go ahead and experiment with these filters – you can always use the history to go remove the effect.
The Unsharp Mask filter, so named because it serves to mask unsharp elements of an image, is the tool that most people use in the digital darkroom.
The Unsharp Mask filter analyses the contrast between adjoining pixels in your image. The higher the contrast, the more likely it is that it represents an edge. Further increasing the contrast will serve to increase the sharpness. Thus the Unsharp Mask filter increases the darkness of the dark side of the edge, and increases the lightness of the light side. Therefore, the Unsharp Mask filter actually increases contrast along edges, which gives the appearance of a sharper image.
On opening the Unsharp Mask filter in Photoshop (other programs will be similar) you will note a dialogue box with a preview area and three slider controls – Amount, Radius and Threshold. In other programs, these controls may have different names so consult your user manual. They should, however, have much the same effect.
Amount refers to the amount of sharpening that will be performed, in other words the strength of the sharpening, or how much the contrast will be enhanced.
The Radius is perhaps the most important of the settings, as this is where you specify how wide the sharpening halo will be – how many pixels either side of the edge will be effected by the sharpening. Setting this too wide will show why it is referred to as a halo, as this effect will be pronounced. The amount of Radius required will differ significantly between different types of image, and you should be careful in using this tool not to over sharpen and create a visible halo.
The Threshold slider allows you to specify the difference in contrast that will be used to determine an edge. Differences below the threshold will be ignored by the program, and thus you can avoid over sharpening areas that have subtle differences. Overuse of this control can increase the graininess of an image, so be selective in using it.
Before you use the Unsharp Mask, there are a couple of key considerations to bear in mind.
Sharpening should always be the last step in your work flow, as other actions (changes in resolution, removing dust and scratches, changing colour balance) are likely to alter the effects of the sharpening.
Related to the above is the fact that sharpening should always be performed at the desired output resolution – if you plan to print at 200dpi, make sure your image resolution and dimension are set accordingly before sharpening.
When you open the Unsharp Mask filter, ensure that the Preview tab is selected, so that you can see the effect of sharpening as you work.
Make sure that you are viewing your picture at 100%, so that you can see the actual pixels. Pressing Ctrl+Alt+0 (even when the filter is open) will increase the image to 100%.
Select a key feature of the image to be in the image preview in the dialogue box, such as an eye.
To minimise the Halo effect, try to keep Radius below 5.0 – the lower the better.
To reduce noise, keep Threshold set at 0.
A general procedure for working with the Unsharp Mask tool is as follows
Start with the Amount set somewhere between 150% and 300% - around 200% is a good rule of thumb starting point.
Set the Radius to 2.0 and the Threshold to 0.
Adjust the Radius until it suits the image content. Sharpness is fairly subjective, but for most images a setting of no larger than 5.0 works nicely – any more than that, and the halo becomes increasingly pronounced. If possible, aim for radius settings around 2.0 or less to minimise the halo.
Adjust the Amount slider as necessary to get the appropriate level of sharpness.
Finally, may need to adjust the threshold to reduce any over sharpening on non-edge parts of your image. Only do this if absolutely necessary.
Play around with this filter – once you get the hang of it you’ll find that it is a powerful tool, and can really allow you to accentuate the fine details in the scales of fishy subjects Don’t forget the History tools that allow you to Undo any sharpening if you don’t like the results.