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Notes on Sharpening

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  #1  
Old 02-10-2009, 04:34 AM
undavide undavide is offline
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Lightbulb Notes on Sharpening

Dear All,
I signed in to the forum long time ago but I admit I'm no frequent poster... I was first very impressed and appealed by the tutorials made by byRo about sharpening, and I come back here from time to time to check for new inputs.

Now, it happens I've written an article about sharpening: which may not be intended as a tutorial tout-court, even though it has all the walkthrough to duplicate the tecniques exposed; it may be better defined as a personal collection of notes about the subject and a bunch of different, esotic way to apply sharpening and solve common problems like: modulate and differentiate the effect of sharpening in edges and texture, the use of surface blur as a sharpening kernel, pyramid decomposition (gaussian, bilateral and mixed) as very efficient sharpening platform, etc.

Friends say me it's a bit technical, but I guess they have been impressed by the terminology only (they feel "pyramid decomposition" is scary maybe? Spooky difference of gaussians? ;-)
Anyway, I've put all my efforts to make it readable and every assumption can be verified within Photoshop. I'll be glad to hear your comments and suggestions about it: the website that gently hosts it, has made a comment section available for those who would like to give feedbacks (lot of visitors but few people that stops to say hello, I must really be scary :-) and I'll keep the thread checked here as well.
The english version is there:

Notes on Sharpening article


Currently I'm developing some Photoshop CS4 panels that automatize and give an (I hope) nice neat GUI to some of the operation suggested - for those who don't know about it, with CS4 it's now possible via Flex/ExtendScript to make custom built and designed Flash "object" that are loaded in Photoshop as panels (just like Info Palette, Layers, Channels, Hystograms, etc). Somehow they will be made available there in the future, I guess.

By the way, in doing that, I've now realized thad the sharpening equalizer byRo proposed years ago is made by DoG (Difference of Gaussians) layers. The concept behind it is different but similar to the one I've suggested with pyramid decomposition, it could be interesting to implement a true decomposition made by DoG. The todo list increases worryingly ;-)

Anyway, many thanks for your attention and kind regards,

Davide Barranca
Bologna, Italy
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  #2  
Old 02-10-2009, 11:43 AM
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igot2pman igot2pman is offline
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Re: Notes on Sharpening

Great read... but not for everyone...

I too have a quest for perfect sharpening. I came up with a perfect combo a while back involving somewhere around 14 layers, all in one action. It creates a very "fine" sharpen, perfect for skin and hair.

I am def going to make some of what I learned in the article part of my arsenal.

Thanks,
-Keven
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Old 02-10-2009, 01:25 PM
neumanns neumanns is offline
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Re: Notes on Sharpening

You lost me at weighted least square...But I'm quite pleased I was able to follow to there.

Care to share what "weighted least square" does in laymens terms...I followed a few links but all I got was formulas, and my brain don't handle them very well!
.
.
.I'm curious what potential lays behind this mysterious door.
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Old 02-11-2009, 02:56 AM
undavide undavide is offline
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Re: Notes on Sharpening

Hi neumanns,
think of weighted least square as "a better surface blur filter"!
I've read the math behind it and I won't tell you I've really understood it, but, if you get a look to their video here or here (smaller) you'll see a pyramid decomposition using WLS in action. I'm showing in my article how to build a Gaussian and a Bilateral one - if Adobe would implement that WLS in photoshop...
Pyramid decomposition simply let you tweak the contrast in (as many as you want) different frequency ranges, depending on the levels of the decomposition - so, if you will, high frequency (finer detail, such as hair), mid frequency and low frequency (more broad transition, such cheeks in portrait, something that doesn't change too quickly). Different kernels (gaussian, bilateral, WLS) lead to different look - gaussian produces halos, WLS is halo-free, etc.
Glad you've enjoyed it anyway!
Ciao,

Davide
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Old 02-11-2009, 07:22 AM
undavide undavide is offline
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Re: Notes on Sharpening

Quote:
Originally Posted by igot2pman View Post
I came up with a perfect combo a while back involving somewhere around 14 layers, all in one action.
Thanks Keven,
but now that you have appealed us, you must share your thoughts as well
Kind regards,
Davide
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Old 02-11-2009, 03:49 PM
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igot2pman igot2pman is offline
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Re: Notes on Sharpening

I recounted the layers, and its 11...

Spent like 3 days strait tuning it. its now basically perfect in that it sharpens with basically no lighten or darken and no halo's. The picture below has only been sharpened.

I normally don’t even show a screen shoot of it. But as you asked, here it is. I don’t think i am willing to share how it’s done, as around here sometimes people just take... if you know what i mean. Or don't even say thank you...

But its 5 different methods into one.

-Keven
Attached Images
File Type: jpg GS4K2717-org.jpg (67.9 KB, 137 views)
File Type: jpg GS4K2717-KA.jpg (97.5 KB, 139 views)
File Type: jpg Keven-Alvarado-Sharpen-Clean.jpg (52.8 KB, 120 views)

Last edited by igot2pman; 02-11-2009 at 03:58 PM.
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  #7  
Old 02-11-2009, 08:33 PM
neumanns neumanns is offline
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Re: Notes on Sharpening

A while ago i decided I wanted a better understanding of how photoshop was doing it's magic. While I still don't fully understand what is going on behind the scene understanding the concepts even if only at a conceptual level has helped me improve my usage of the program.

I'm not even gonna pretend I know how they filter the frequencys in the samples they use in the video...But it sounds very interesting to say the least.

Anybody that has spent much time learning sharpening has also learned how to combat the dreaded halo. The "weighted least square" filter does seem interesting if for no other reason than why combat halos when you can avoid them in the first place.

Thank you for sharing your information and studies so openly...I admire people who do that. Most people seem to want to keep there knowledge to themselves or try and sell it for a buck.

I am gonna have to look into this deeper at a latter time...thanks for sharing.
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Old 02-11-2009, 09:45 PM
gmitchel gmitchel is offline
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Re: Notes on Sharpening

There is no quick and easy answer to the question: what is weighted least squares?

Ordinary Least Squares (OLS) is the basic linear regression model. The idea is predicting change in some variable (y) using one or more independent variables (x's).

OLS has certain assumptions for unbiased and efficient estimates. These are called the Gauss-Markov assumptions.

Weighted Least Squares (WLS) is employed for a couple of violations of the Gauss-Markov assumptions. One is called homoskedasticity. The other is independence of error terms and the independent variables (the x's).

Linear regression assumes that every data point provides equally precise information. Digital imaging involves noise, which challenges the Gauss Markov assumption that observations are measured without error.

Without reading article here, my surmise this is the use of WLS being referenced.

Cheers,

Mitch
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Old 02-12-2009, 06:14 PM
undavide undavide is offline
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Re: Notes on Sharpening

Quote:
Originally Posted by igot2pman View Post
I normally don’t even show a screen shoot of it. But as you asked, here it is. I don’t think i am willing to share how it’s done, as around here sometimes people just take... if you know what i mean. Or don't even say thank you...
Dear Keven,
I can understand that you are jealous of your work (very remarkable indeed!) For instance, I've freely written about all the techniques - also because I really believe in sharing as a form of knowledge growing: in my article I ask for comments but also for suggestions about how to improove the theoretical aspects. On the other hand, I hope to get some small revenues (with the panels and the scripts) to cover the time spent in writing - since my family keeps having that strange habit of eat two or three times a day (all the days of the week).

Somehow, I guess the theory should be available for everyone, while its application is something you've got to be rewarded for.
Anyway, thanks for showing your routine - while the layerset is a bit cryptic, the result seems very good.
Kind regards,
Davide
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  #10  
Old 02-13-2009, 01:27 AM
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igot2pman igot2pman is offline
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Re: Notes on Sharpening

Davide,

I agree the theory should be available to everyone and it is. I learned everything there from RTP and just put it all together.

Nothing cryptic. They are named what they do, not how you do them. If i could sell them, and make scripts, I would. But in all reality, not many would pay much.

I will tell you this, the "KA - Basic sh" is basically the Manuel Libres Librodo Jr. sharpen.

If anything, your method is not only more technical, its more difficult.

-Keven
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