Notes on Sharpening © Davide Barranca. Rev. 1.0.1 - January 2009

1. Introduction

This article is a work in progress collection of personal notes on the subject of sharpening; I’m no digital image processing scientist so, even though I like to play with theoretical problems, I try to find my answers within Photoshop (as I suppose they all do in Dan Margulis’ Color Theory Yahoo group, to which attention I first would like to turn this one). Chances are that I won’t be rigorous too, my aim is to better understand the subject and share my findings with people who would like to integrate them, or simply give a feedback on the techniques exposed. If you’re not interested in all the (very trivial indeed) math and graphs, feel free to skip to the how-to sections: nevertheless, I hope everything will be food for thoughts.

What I'm suggesting with this article is, among the rest, the possibility to target with appropriate sharpening different image features, even if they belongs to the same spatial frequency range (plus an experimental approach to high-radius low-amount sharpening). Then I'm showing how to use bilateral and mixed pyramid decompositions to modulate the sharpening within all the image frequencies.

(Fig. 1.1) Before and after version, applying some of the tecniques exposed in this article.

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"Shadow/Highlights" clarification please George Machen 2009-01-07 01:58:49 > 8. Bilateral and WLS Pyramids > > ...Shadow/Highlights with SB (instead of GB) in its > “engine” gives the same halo-free look by the way... I don't have CS4. Are you saying that its Shadow/Highlights dialog now features an option to choose whether it uses Gaussian or Surface Blur? If not, what did you mean exactly in this statement? Thanks! (G-R-E-A-T write-up, Davide!) Reply

Davide 2009-01-07 22:53:37 Hi George, I'm glad you liked it! No, unfortunately there's no GB/SB option in CS4. But you can always custom build your Shadows/Highlights: for instance, create a curve adjustment layer to lighten the picture, then add a luminosity mask to it (or choose the channel that better suits the image needs and use it as a mask). Now you can experiment using GB and SB for blurring the mask: the first one gives you a standard Photoshop S/H feeling, while SB (as long as the algorithm doesn't reverse) shows less or no halos. Ciao, Davide Reply

Alexey Rybakov 2009-01-07 19:58:18 Thanks for nice article with informative illustrations and examples. I'll glad to read more if you'll develop this farther. Reply

Re: "Shadow/Highlights" clarification please Stephen Marsh 2009-01-08 12:48:48 Thank you Davide, this is a great exploration, I am eagerly awaiting some actions! George, I presume that Davide is referring to manually simulating what the Shadows/Highlights command does. Dan Margulis described a method for this and one of the Applied Color Theory list members created an action. This action is available to list members from the files section. Margulis PSU ON2004.atn http://tech.groups.yahoo.com/group/colo rtheory/files/ How to re-create the Shadow/Highlight effect of Photoshop CS as described by Dan Margulis in the Oct/Nov issue of Photoshop User titled "Making Two Ends Meet", pg. 44-47. Regards, Stephen Marsh http://members.ozemail.com.au/~binaryfx/ Reply

Bravissimo !!! Andrea Baldini 2009-01-08 23:02:13 Devo dire che é una roba incredibile ! Davvero superba la genialità del progetto, non avevo mai visto nulla di simile! Complimenti anche per le illustrazioni realizzate molto bene. Spero che l' articolo venga tradotto anche in italiano. Complimenti ancora, Saluti Andrea Baldini Reply

good work Jack 2009-02-10 23:13:44 I'd love to test the actions when you create those. Also it would be nice to see samples on photographs as apposed to the painting your using here. It's difficult to see the sharpening. Reply

thank you! Timo Kirves 2009-03-14 17:51:02 Dear Davide, The whole series of your techniques open dramatically better chances to succesful fine art photographic prints with todays inkjet printers. I work as a photographer and instructor in Helsinki, Finland, working on both own and colleagues´photographic prints. Thank you for shearing this work of yours with the rest of community. Best Timo Kirves Reply

Davide 2009-03-14 22:48:29 Dear Timo, thank you very much for your comment, knowing that some of my thoughts may help someone out there getting better results and enjoying his pictures is a great reward for me. I wish I had more time to explore other interesting topics - I've something about local contrast in mind but I'd like to dig a bit deeper before publishing. Kind regards, Davide Reply

adding channels Bruce 2010-02-26 23:41:25 Hi; I am very interested in your sharpening schemes. However, I am feeling a little inadequate... How do you add the subrtraction channel back into the L channel in the gaussian blur method? Thanks, Bruce Reply

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