Without getting into the science of it, suffice it to say that most camera sensors are not capable of capturing the image resolution of our finest lenses.\u00a0 That’s only now starting to change with the full frame and medium format sensors with resolutions of 20 M pixels and more.\u00a0 In fact, there is some discussion of the opposite problem is starting to occur; that being, that the resolution of the sensor exceeding the ability of the lens to resolve.\u00a0 So one of the main reasons for sharpening is to overcome some of the limitations of our sensors.<\/p>\n
Another reason for sharpening is that post-processing introduces distortions in our images, distortions that manifest themselves in softer looking prints.\u00a0 Sharpening can restore a more crisp look.<\/p>\n
Yet another reason for sharpening is that it makes our photographs look great.\u00a0 You’ve probably noticed that your images sparkle more after they’ve been sharpened.\u00a0 They have more brilliance.<\/p>\n
And finally, there’s something that is very satisfying to many of us when we look at a razor sharp image.<\/p>\n
What does sharpening do?<\/strong><\/p>\n Sharpening does not actually sharpen an image.\u00a0 If you have an image that is out of focus sharpening cannot bring it back into focus.\u00a0 For that reason, the term ‘sharpening’ is a bit misleading.\u00a0 No, sharpening doesn’t actually sharpen an image but rather creates the illusion <\/em>of sharpening it.\u00a0 Sharpening first finds the edges in the image.\u00a0 What are edges?\u00a0 They are a rapid change in just a few pixels from dark to light.\u00a0 Next, it darkens a few pixels on the dark side of the edge and lightens a few pixels on the light side.\u00a0 (You can readily see that if an image is out of focus, soft,\u00a0the transition of edges from dark to light is not crisp but\u00a0mushy.\u00a0 Therefore\u00a0there aren’t any edges to ‘sharpen.’)<\/p>\n But to understand what’s going on it is best to actually see the effect sharpening has.\u00a0 We’ll take a very simple example of a single edge between medium dark and medium light areas.<\/p>\n \u00a0 You will notice that the edge is already perfectly sharp.\u00a0 It really doesn’t need any real sharpening.\u00a0 However, the sharpening we’re talking about can add some punch to the edge.\u00a0 To do that we will apply Unsharp Mask, admittedly to an extreme.\u00a0 The values we use are: Take a look.<\/p>\n It’s pretty easy to see the light gray side of the edge is lightened to pure white.\u00a0 You’ll need to look more closely to see that the the dark gray side of the edge is darkened to black.\u00a0\u00a0This results in\u00a0a halo along the edge.\u00a0 The lightened side of the edge is a lot more obvious than the darkened side.\u00a0 As stated above, this is an exaggerated example.\u00a0 Normally one would use a radius of .5 to 1 pixels and an amount of from 50% to 100% and the halo would be much more subtle.<\/p>\n This example also illustrates the effect of over sharpening.\u00a0 Good sharpening is virtually unnoticeable unless you look at the image at 100% magnification.\u00a0 In over sharpened images the halos stand out at any\u00a0magnification.<\/p>\n When\u00a0Should the Image be Sharpened?<\/strong><\/p>\n We’re finally to the\u00a0place in this post where I’ll discuss the way I sharpen.\u00a0 But first,\u00a0the sharpening rule is that it is the very last thing you do in your work flow.\u00a0\u00a0This is because all of\u00a0the adjustments in post-processing tend to soften the image.\u00a0 Sharpening restores the sharpness\u00a0of the original capture.\u00a0 So\u00a0when I prepare an image for printing I have Photoshop\u00a0actions that flatten the image, resize it and, last but not least, sharpen it.<\/p>\n![\"Unsharpened](\"http:\/\/ralphnordstromphotography.com\/wordpress\/wp-content\/uploads\/2009\/01\/sharpening-unsharpened2.jpg\" "\\"sharpening-unsharpened2\\"")
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\nAmount: 250%
\nRadius: 5 pixels
\nThreshold: 0 levels<\/p>\n<\/a><\/p>\n