Talk:Unsharp masking

Apparent Sharpness

Why is the word "apparent" used here? If you take an image and remove the high-frequency components, it doesn't just "appear" soft -- it is soft, since you've filtered out the detail. And correspondingly, if you apply an unsharp mask operator to an image, the result just doesn't "appear" to be sharp, it is very much sharp (or at least sharper), since this operator amplifies whatever high-frequency components were present in the image (proof: fourier transform the operator). mdf 22:56, 10 January 2006 (UTC)

On the same subject, there's a small tautology in the article that ought to be removed. I edited it, but it still says

The resulting print appears sharper than one made without the unsharp mask; the apparent accutance is increased.

The second clause is just a restating of the first; "appearing sharper" is the same thing as "apparent accutance is increased". If someone can explain how the apparent accutance increases (i.e., how the magic trick works), that would be worth noting. +ILike2BeAnonymous 19:19, 15 October 2006 (UTC)

"appearing sharper" is the same thing as "apparent accutance is increased".

As their are different ways of defining sharpness, explaining that we are referring to a specific type is not a tautology. It also helps to visually clarify the meaning of "accutance" and vice versa. I suggest leaving it. Stonesight (talk) 03:03, 19 September 2010 (UTC)

There's no need to answer questions from 2006. If anyone is curious though, the “apparent” in “apparently sharpness” is to distinguish from amount of real detail. Gaussian sharpening (“unsharp mask”) increases the accutance but (obviously) does not increase the amount of detail in the image. –jacobolus (t) 06:45, 19 September 2010 (UTC)

History

The article mentions the first use in Germany in the 1930's. Curiously, the unsharp mask operation is just a single step of the more general iterative deconvolution algorithm described by P. H. van Cittert in 1931. Is this a coincidence? mdf 22:56, 10 January 2006 (UTC)

Unsharp Mask Creates Illusion?

The intro reads: 'creating the illusion that the resulting image is sharper than the original.'. I was wondering if this is actually correct. Shouldn't it be 'resulting in a sharper image than the original but without increase of information'?

This clearly depends on the definition of 'sharper', which is in my opinion 'a more clear distinction between objects', which is exactly what the unsharpen mask does. It does not mean 'more information' I think. 71.206.215.239 01:16, 13 February 2007 (UTC)

I agree. This also answers the question above on the use of "apparent sharpness". Sharpness is given by the strength of the slope between dark and light: the less space an edge occupies, the sharper it is. This is not the same as resolution, which can be interpreted as "the amount of information." Though both concepts are related: the lower the resolution, the lower the sharpness. crisluengo (talk) 14:38, 3 December 2009 (UTC)

I agree too. —Ben FrantzDale (talk) 02:45, 4 December 2009 (UTC)

How about an example?

I think this article would be improved by adding at least before and after images, maybe with intermediate steps.--Jwwalker 03:19, 1 November 2007 (UTC)

Frequency response

As a series of convolutions, isn't an unsharp mask a linear filter? As such, can't we describe it in the frequency domain by a transfer function? If so, is it a bandpass filter? Since it is usually constructed from Gaussian blurs, its transfer function should be nonzero almost everywhere... —Ben FrantzDale (talk) 22:50, 21 January 2008 (UTC)

Duah... the FFT of a Gaussian is a Gaussian, so the transfer function should also be a Difference of Gaussians. Sound right? —Ben FrantzDale (talk) 01:36, 22 January 2008 (UTC)

Well, no. Or yes, sort of. The filters used are not necessarily linear (that is, they can use the "threshold" or other nonlinear mechanisms). But a linear analysis is certainly a useful part of it. They're also not usually Gaussian, because a filter that falls less rapidly in the frequency domain will make a better looking result. The article says Gaussian blur, and that may be true in some cases, but it's unsourced and I wouldn't trust it. And overall it's not a series of convolutions, it's a convolution and a difference and an add, but still there's an equivalent linear filter; it's usually applied in a nonlinear (gamma compressed) domain. Dicklyon (talk) 01:47, 22 January 2008 (UTC)

Picky point... It is not literally true that unsharp masking enhances the spatial high-frequency components. Rather, it attenuates the lower-frequency components. When the "sandwich" is correctly printed, there is a net increase in the high-frequency components. WilliamSommerwerck (talk) 14:56, 10 November 2010 (UTC)

Dubious

I just added the "dubious" tag. Here's the thing: As a linear filter with, unsharp mask doesn't add any new information to an image. It makes the image look sharper by enhancing the high-frequency components, but it doesn't add any missing data. Deconvolution in its simplest form can't either, although it is often done in a more sophisticated way than just an edge-enhancing algorithm. I may just trim that section... —Ben FrantzDale (talk) 01:41, 22 January 2008 (UTC)

I think what that section says seems true, as far as it goes. It would be better if it were sourced. What are thinking is worth removing? Why not add a fact tag if you're not sure? Dicklyon (talk) 01:47, 22 January 2008 (UTC)

Here is a good place to start. Dicklyon (talk) 01:49, 22 January 2008 (UTC)

Sharped ? Or Sharpened ?

Does Wikipedia's version of the English language permit nouns to be 'verbed' at random ?)
I would let 'bolded' text pass, though - 'emboldened' is an ugly word, and tends to mean 'encouraged' ...

--195.137.93.171 (talk) 01:25, 7 March 2008 (UTC)

A schematic illustration would help

I'm having trouble visualizing the analog process with the glass plates. It would be neat to have a side-view illustration showing the light from the enlarger passing through the original negative and the blurred positive, and the resulting brightness level striking the final print.

In my head, it feels like all this should do is make dark areas lighter because the dark areas of the positive are blocking the light which (because enlarging is working with a negative) would darken regions of the print. I'm failing to visualize the process, so if someone who understands it could sketch out a diagram rather than just before/after pictures (which any of us can see in our paint program, thank you), it would be very helpful. Myself248 (talk) —Preceding comment was added at 01:12, 13 May 2008 (UTC)

Presumably one using this process would increase the exposure to compensate for this problem. If you had a low-frequency sine wave, it would look almost exactly like a Gaussian-blurred version of itself, so if you make a positive of it and project its negative on it, you'll get a uniform brightness out the other side. If you have a high-frequency sine wave and blur it, you get medium gray. Project the original negative through that medium gray and you just have to compensate for exposure but will still get the same high-frequency pattern. Does that help? —Ben FrantzDale (talk) 02:06, 13 May 2008 (UTC)

digital: high boost filtering

In computer vision and image processing there is an algorithm that, based on an input parameter--i have no idea which parameter matches with the photoshop description here--turns unsharp masking into high boost filtering. there is no article on high boost filtering or any mention of it on this page. there is also no algorithm for unsharp masking here on the page. addressing this would also solve the problem of citations for this page: any textbook on IP can give you that algorithm. Albert Cruz 02:38, 14 July 2009 (UTC)

Not sure what you mean by "turns it into"; unsharp masking is just a form of high-boost filter. Although some do distinguish the two. I agree that it would be good to cite such sources for the their algorithms and terminology; I think you'll find that i t varies. Dicklyon (talk) 02:54, 14 July 2009 (UTC)

'Creative Effects'

The article mentions using the unsharp mask to for creative effect. What does this mean? It seems like it needs a reference or example.

However, it is easy to create unwanted and conspicuous edge effects. On the other hand, these effects can be used creatively, especially if a single channel of an RGB or Lab image is sharpened.

Sjf (talk) 14:20, 22 March 2010 (UTC)

The article should be called Image Sharpening

There are hundreds of techniques in image processing for sharpening an image. Unsharp masking is just one of them. The article should be called Image Sharpening, and Unsharp Masking should be presented as one of the techniques. Renato (talk) 21:12, 8 August 2010 (UTC)

In fact, as I said earlier today, it should also be merged with edge enhancement and acutance to make a comprehensive article. Papa Lima Whiskey (talk) 21:43, 8 August 2010 (UTC)

That sounds reasonable to me. Unsharp masking is really a darkroom technique (which deserves to have its varieties and nuances explained better), and the Photoshop tool called “unsharp masking” should by all rights be called something different, perhaps “gaussian sharpening” or similar. I think we’d be best off if an article here talked about the physical creation of unsharp masks on film (and possibly if it was moved to "unsharp mask", the noun), for the darkroom, and then if the digital stuff was moved to an “image sharpening” article, with a link near the top of the unsharp mask article pointing those readers interested in digital techniques there. –jacobolus (t) 16:51, 10 November 2010 (UTC)

On second thought, the article about the darkroom technique(s) should probably be called “contrast-adjusting masks”, since unsharp masks are only one of several kinds of contrast adjusting masks which can be used. –jacobolus (t) 16:54, 10 November 2010 (UTC)

I agree that the merge proposal has some valid points and should be reviewed.

As it is now, "Unsharp masking" (and "Acutance") talk about specific implementation from a developer/mathematician point of view, i.e. without a comprehensive review of typical applications and consumer/industry/marketing conventions and names, and "Edge enhancement" talks mostly about the same unsharp mask algorithm but from a consumer point of view, with only a few implementaion details.

If there is actually no practical difference between these two terms, these two articles are best merged, and "Edge enhancement" (or "Image sharpening", or whatever it will be called thereafter) should be the main article; otherwise it should be expanded with description of alternative techniques involved (if any). --Dmitry _{(talk •contibs )} 20:16, 12 November 2010 (UTC)

I think Image sharpening is the most reasonable (explicit, understandable, proper article scope to cover necessary background and specific details without a lot of dup'd info across pages) title. Accutance is potentially useful as its own article, but with quite different content than it currently has: given the title, its scope should be the physiological/psychological aspects, demonstrating contrast sensitivity at various scales for lightness/color content, and describing acutance-related optical illusions, etc. –jacobolus (t) 00:30, 13 November 2010 (UTC)

We need someone to perfrom these edits... should we try to recruit an expert on Portal:Photography, Portal:Algebra, etc? --Dmitry _{(talk •contibs )} 18:03, 13 November 2010 (UTC)

I’d have to spend a decent chunk of time figuring out how I wanted to present the article if I planned to rewrite it seriously. I could probably do a quick hacky job more easily, but that would still take a bit more time than I have in the next couple days. Feel free to try to recruit help wherever willing help is to be found, I say. –jacobolus (t) 03:39, 14 November 2010 (UTC)

This is now an old discussion, and more importantly, Its subject is best left unmerged. Clearly in the case of acutance, but also for the various image sharpening techniques. Image sharpening is justified as a notable topic, but unsharp masking is a notable technique. Edge enhancement is also a notable group of techniques. Deconvolution is not an image sharpening technique, it is an information recovery technique family that results in image sharpening in most cases. Other techniques should be discussed only on the image sharpening page, unless they too are notable. Unsharp masking and edge enhancement should only be summarized in image sharpening. 204.191.88.96 (talk) 21:15, 30 November 2012 (UTC)

further discussion. Unsharp masking is notable both for its historical significance and widespread use. In particular, a digital filter that emulates the blurring accurately is still unsharp masking. Edge enhancement is strictly different because it does not modify the entire image usually. It uses edge detection to selectively modify the image. Convolution is different because it is a lot more mathematically complicated. In general, it is an estimation of the blur caused by being out of focus, but notably, some modern telescopes are also deconvoluting atmospheric distortion to get clearer star images. (There is one that actually changes shape based on estimated atmospheric distortion). And there is this ring thing that appears around stars that has a precise mathematical description and can therefore be deconvoluted easily. 204.191.88.96 (talk) 21:15, 30 November 2012 (UTC)

The problem is that the name "unsharp masking" used in digital tools is rather different than the darkroom technique. I don’t know what you mean by “emulates the blurring accurately”. The unsharp mask tool could be called “gaussian sharpening”, because it’s produced by computing the difference between the original image and a gaussian-blurred version. It is a convolution. When you say “convolution is [...] more mathematically complicated”, what you’re actually talking about is “blind deconvolution”. –jacobolus (t) 02:46, 1 December 2012 (UTC)

pretender to the throne

In the 11/2010 issue of Electronic House, there's an article about one Paul Darbee, who claims to have invented an image-enhancement system -- Visual Presence -- which, to anyone knowledgeable, is obviously unsharp masking. Perhaps I'll find time later today to contribute... WilliamSommerwerck (talk) 15:00, 10 November 2010 (UTC)

Comparison with Deconvolution section needs revising

Only the first paragraph of the "Comparison with Deconvolution" section is actually a comparison. The remaining paragraphs simply explain deconvolution. As such, that content should be relocated to the main deconvolution article. If they have no content that isn't already present in the deconvolution article, they can be removed. — Preceding unsigned comment added by Superbatfish (talk • contribs) 14:24, 15 June 2012 (UTC)