Theory and Practice of Sharpness in Digital Images
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by Jeffrey Sward
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Sharpness Theory | |||||||
Direct unaltered digital images appear unsharp, regardless if the source of the image is digital capture or scan of a film original. The reason unaltered digital images appear unsharp is that human "perceived sharpness" is quite different than "actual sharpness." The physiological basis of the "perceived sharpness" effect is common to both film and digital images and is beyond the scope of this discussion. In order to increase the human "perceived sharpness" various digital image sharpening methods have been devised, as described in the next section. |
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Sharpening Methods for Digital Images | |||||||
Early in the development of digital imaging various algorithms ("sharpening methods") were created to increase the "perceived sharpness" of digital images. Direct digital image capture systems (such as digital cameras) usually include sharpness settings. For example, the sharpness settings are often "low-medium-high" or "low-regular-high." In almost all cases, the "low" setting actually results in not altering the original image pixels whereas the "medium" or "regular" settings result in alteration of the original image pixels by application of a sharpening algorithm. Raw image format often bypasses the sharpness settings. Scanner software often includes sharpening options. In general the "sharpening off" setting results in no alteration of image pixels where the "sharpening" setting results in the application of a sharpening algorithm. The Photoshop image editor has several sharpening algorithms, such as "unsharp mask," and "smart sharpen." Third party sharpeners exist, such as Nik Sharpener Pro. |
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Workflow Best Practices and Sharpening Strategies | |||||||
Most literature on digital photographic workflow suggests that the best practice is: "apply all sharpening as the last step. Perform all image edits on an unsharpened image." Direct comparison tests by this photographer using the same edits on the same image, starting both with an unsharpened original and a sharpened original have verified that the best practice appears to be as noted above, "apply all sharpening as the last step." Most literature on digital photographic workflow also suggests that the sharpening algorithms available in Photoshop are superior and more versatile than any of the sharpening algorithms in either scanning software or digital cameras. Therefore, this author's workflow pertinent to sharpening implements these best practices as follows:
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All written content of this web site is solely the editorial opinion of Jeffrey Sward. All images, graphics, and written content of this web site, including the html files, are creative products covered by copyright law. All content copyright Jeffrey Sward 1975-2019. All rights reserved. No portion of this web site or its constituent elements may be reproduced in any form, by any means, without prior written permission. So there. |
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