Image SharpeningPosted: August 16, 2011
The sharpness of the image recorded on your camera is affected by many factors: focus, lens, aperture, shutter speed, raw or jpeg format.
The process of sharpening is done through software tools by increasing the contrast along edges of pixels and enhancing them to heighten image definition. Applying sharpening to your images is both a technical and creative process. It can help emphasize texture and detail and it is essential when resizing for the final output. The difficulty always lies in knowing how much to apply.
Sharpening should be thought of as a multi stage approach within your workflow. There are three stages where a file can be sharpened: Raw Capture, Post-Processing and Output.
Please note that it is very important to judge the sharpness of an image by zooming in 1:1 (100%).
Raw Capture Sharpening
A loss of sharpness is to be expected during the in-camera demosaicing process and therefore it is important to compensate it by applying an appropriate amount of sharpening during the raw conversion stage. When applying sharpening here, it is important to consider the image content, exposure and noise level of the image. If this action is applied without paying enough attention to the details, sharpening artifacts can be created that may become problematic further into your workflow.
This stage of the process involves sharpening the image after it has been converted from Raw format to the Tiff format in RGB colour mode. At this point, you can sharpen the image using Photoshop’s built-in filters like SmartSharpen, Unsharp Mask and High Pass. You can also deploy more sophisticated 3rd party Photoshop actions like Photokit Sharpener or sharpening plugins like NIK Sharpener Pro and FocalBlade. How much sharpening to apply depends on your creative aesthetic and intention for the image. When sharpening the image it is important to take the content into consideration and to keep within its limitations. You want to emphasize the edges without compromising the texture, as in skin tone and without introducing fake texture into the flat areas, as in backgrounds and skies. It’s always important to keep in mind that the file may be resized or that further sharpness may be applied in the final output, therefore it is essential to keep the sharpening to a reasonable amount.
Sharpening in the output stage is highly customized and fully dependent on the actual print size. As a rule, the larger the print size, the more sharpening is required to be effective.
Raw Conversion with Adobe Camera Raw
Below are two before and after examples of sharpening being applied in the Raw conversion stage in Adobe Camera Raw. (Examples are based on Nikon D700 12MP Raw original.)
As you can see in the above example, sharpening at the Raw conversion stage does not need to be too aggressive to get the desired effect.
Post-Processing in Adobe Photoshop
Below are two examples of good sharpening versus excessive sharpening using Unsharp Mask filter in Photoshop at 100% views. (Examples are based on Nikon D700 12MP Raw original.)
The second example above clearly suffers from over-sharpening. The edges in the details have halos all over and the final look is too artificial. The Radius setting in the Unsharp Mask is a bit too heavy thus resulting in undesirable heavy dark keylines in this image.
In summary, when sharpening any image file it is important to take the content of the image into consideration and to keep within its limitations. You want to emphasize the pixel edges to bring out sharpness and clarity without compromising the texture or introducing pixel artifacts. It is important to remember there are normally three stages of sharpening: Raw Capture, Post-Processing and Output. The converted raw files may be resized and further sharpening may be applied in the final output. Therefore it is crucial to keep the sharpening to an appropriate amount prior to the final output stage.