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by Bart Arondson

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33

Some background: The unsharp mask is an old technique that has been used in darkrooms long before computers were capable of processing images. The original process consists of two exposures; first you create an unsharp mask by making a contact copy on low-contrast positive film, but with a distance between the original and film (and sometimes a diffusing ...


14

Sharpening of digital images is made necessary by two things that degrade the image: 1) the anti-alias filter, to prevent aliasing it filters out high frequency information, but that degrades the image sharpness. 2) the Bayer matrix, this is a scheme to recover pixel level colours from a 3x3 matrix which also degrades image sharpness. This degrading of ...


14

It is a property of the lens. the bokeh highlights image not only shape of the aperture, but it also gets a profile. It can be a square profile, have sharp edge and then attenuate, have dots inside it, show cats eye, or be smooth like yours. The way the lens is corrected for spherical aberrations affect this. Vintage lenses typically make sharp bokeh rings. ...


13

The unsharp mask will increase the perceived sharpness of an image by increasing the contrast of pixels next to each other. It does so by making darker pixels a bit darker, and brighter pixels a bit brighter. The amount parameter will control how much darker or brighter the pixels will be made. The threshold parameter will prevent the filter from having ...


11

It's mostly the resolution of the image that affects the sharpening. When using unsharp mask, a radius of 0.1 mm is a good starting value. For an image displayed on a computer monitor at about 100 PPI, that translates to a radius of about 0.5 pixels. Then there are also differences in the media that causes the sharpening to have varying effect. A printing ...


11

There's two mistaken statements in your simple question: first, that sharpening is always needed for digital photographs, and second, that it's not needed in film. Let's start with the second. Film actually isn't fundamentally different here. Scanned photos often benefit from digital sharpening to match the output medium. But not even digital: the common ...


8

These days, I would think pros use tools like Adobe Lightroom as much as Photoshop. Lightroom 3.x specifically is particularly well suited to removing noise as it uses a newer, more advanced algorithm to do so. It may also be the case that the latest version of ACR (Adobe Camera RAW) for photoshop has the same noise reduction tools if you happen to be using ...


8

If you remember the exact radius of the Gaussian blur, and you processed and saved the images in a 16 bit or greater format then you can remove the blur by inverse filtering in Matlab. If you don't remember the radius, or you truncated the pixel values by working or saving the image as 8 bit (and then used lossy JPEG compression for good measure destroying ...


7

Unsharp mask works just fine when sharping for print, the original method was actually used when creating prints in a darkroom. You just have to know how to adjust the parameters for the specific resolution. A good base value for the radius is 0.1 mm, which you have to translate to a value depending in the resolution: radius = 0.1 mm * ppi / 20 So, for ...


7

Simple answer is YES! Noise is an undesirable artifact, and many operations can enhance its appearance, not just sharpening. Tweaking curves, adjusting contrast, working exposure, etc. can all have some impact on the noise that is present in an image...although sharpening tends to have the greatest impact. It is important to handle the bulk of your noise ...


7

In general, yes, RAW files will need sharpening. This is for two main reasons: First, the processes (both at the physical sensor level and in software) to convert the raw data to a useful image tend to result in soft-looking images. for more details, see the answers in Why should my last post-processing step be sharpening? and Why do photos look best ...


7

You should really only sharpen once, and base that on your intended output. If you shoot a JPEG in camera, as you suggested it can apply sharpening depending on your settings. If you shoot RAW the in camera settings typically do not apply. In Lightroom, I would suggest sharpening in the develop module. The develop module gives you much greater flexibility ...


6

Whenever you see a truly breathtaking image, you can be sure that it's the culmination of doing a whole lot of things really, really well. In the examples you indicated, we're looking at images scaled to a size much smaller than the files produced by your camera, which suggests that at least some of the impact you're perceiving in the photos you're trying ...


6

The short answer is: yes, sort of. I don't think there's a absolute rule for sharpening in any given genre, but there are some rules of thumb that may get followed from time to time. For example: Portrait photography typically likes to focus in on the eyes and soften out skin blemishes such as scars, acne, etc. So, your sharpening technique there is ...


6

I'm no expert, but my understanding is that the primary thing that causes bokeh-circles to be sharp is the (apparent) size of the light source. Smaller light-sources will cause sharper bokeh-circles. To understand why that is, you must first understand what causes bokeh; please see this answer for a detailed explanation. Once you've read that, it's easy ...


5

Assuming you're talking about downsizing the image, the reason you would sharpen after the resize is because resizing, itself, usually results in some sharpening. That allows you to tailor any remaining sharpening needs based on the current state of the image. Now, if you're upsizing the image, then a consideration is that sharpening often has some ...


5

I don't use Lightroom but I regularly use Adobe Camera Raw which is pretty much the same thing but built into Photoshop, and have observed the same effect. By default ACR applies chroma noise reduction to the raw image. The noise reduction only seems to be applied in the preview when you zoom in (perhaps Adobe figured the noise wouldn't be visible in the ...


5

Resize and then sharpen is the answer. It is commonly said that sharpening should be the last step. This make sense because you do not want to stretch the effects of sharpening. Sure you could do more complicated things but the lest steps are applied the less change there will be of seeing artifacts in the final image.


5

You are probably working with RAW files. RAW files include a preview of the image rendered as the camera would have made a JPEG, which includes some sharpening applied. When you first load the image in a program like aperture, the preview JPEG is displayed until the RAW file can be processed. Since the RAW file has no sharpening applied, it appears to get ...


4

To understand what's going on here, it's useful to know a bit about how Lightroom handles your images under the hood. When you import photos you may notice Lightroom telling you it's generating "previews". These are JPEG images, usually smaller than the full-size image you've imported, which Lightroom generates automatically and stores in its catalog ...


4

I'd like to chime in, albiet a bit late. Sharpening is not a one-size-fits-all thing. In an ideal world, you would sharpen each image individually for optimal results. This isn't an ideal world and most people who process volumes of images want some compromise setting that gives a good effect most of the time. Rule of thumb 1: Never sharpen at other than ...


4

Always do sharpening last - if you do sharpening and then NR, you are going to first amplify noise and then undo the sharpening (because, as you already know NR will cause some blur) Also, sharpen for your target medium (big jpeg, small jpeg and print all require different amount of sharpening) and make sure sharpening only happens once, for example if you ...


4

Bojidar Dimitrov has a great article about unsharp mask here. The article has example images and it also visualizes the parameters.


4

If I understand your comment, you are not viewing the preview and/or the full image both at 100%. This is absolutely necessary for accurate preview of sharpening. You should always be looking at a 100% magnification of your image. It is the first step in Adobe's help topic on sharpening Zoom the document window to 100% to get an accurate view of the ...


3

Thanks for the site link, Mary - now I can see exactly what the problem is. It's really off-topic for this forum (it's a web development issue rather than a photography one) but I'm sure others may be interested in the answer too. I see that on the iPhone I get the mobile version of your site. If I click on About it takes me to this page. And here's the ...


3

First of all, everyone has their own tastes, and if you are used to unsharpened photos, they will look best. Oversharpening can make a photo look fake, which might be what you are seeing. Also, if you zoom in really close, it creates rainbow effects. However, an appropriate level of sharpening will usually improve the image. The appropriate level depends on ...


3

It almost certainly uses an image analysis technique called "deconvolution." Reading the wikipedia page on it is a good start but it is awfully technical and you might be left just knowing the name of the technique. I did read a blog somewhere where is suggested that the inverse transform that is needed for proper deconvolution can be known since the blur ...


3

Instead of merging the layers together, try to convert them to a Smart Object. The smart object contains all the original layer data (which also can be later edited — just double click the smart object), but appears as a "single layer" in the Layers window. If you now apply the Unsharp Mask filter to the smart object, it is created as Smart filter and ...


3

Things are worse than you imagine. Not only is there no ideal sharpening for an image taken by a specific camera and lens combination, with lens set to a specific aperture, the correct sharpening depends on the output medium and the viewer or photographer's taste. Sharpening is therefore as subjective as anything can be. So the answer is sharpen to taste ...



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