Sharpening with highpass filter

[winwintoo]

Some time ago, someone posted a method for sharpening an image that included the highpass filter and then some fiddling with "undo" under the edit menu.

I used it with great success, but have forgotten the steps and can't find the tip in the forums.

Thanks, Margaret

[CJ Swartz]

Margaret -- here is one of the threads with info about High Pass sharpening. I'm sure there are others, but this is a start.


high pass sharpening tips

[Flora]

Margaret,

I was browsing through the tutorials a while ago and read this one about sharpening without an aura .... could it be the one you were looking for?

[winwintoo]

Thanks Flora - that's what I was looking for, but I was looking in the wrong place - I'm so glad you found it for me.

CJ, I looked at Trimoon's suggestions too and will be adding them to my repertoire.

Take care, Margaret

[Flora]

Margaret,

So glad I could help!

Since discovering it, I've been using it quite a lot as well .... and been very happy with the results ....

CJ,

thank you for pointing out Trimoon's tip ... you know me, the 'experiment junkie'... ...always happy when there's something new to try!

[Stephen M]

Hi folks, I have many thoughts on sharpening, and high pass filtering has it's place among them - just as unsharp mask and other methods have their place in the process.

Some general links on sharpening can be found here:

http://members.ozemail.com.au/~binar...V_links.html#F


For most Photoshop users high pass filtering is a fairly new thing. Audio processing and image processing are quite similar in some ways. I was blown away the first time I played with audio low/high pass filtering (I should have chosen audio and
not prepress as a career).

Things one should look out for when sharpening with this mehod include: noise amplification, excessive edge halo width (too high high pass settings). Just some of the regular things as with USM but as you have less control with high pass you have to take more care.

The basic operation of USM is done by subtracting a blurred original from the original. The image is made sharper by removing low frequency data from the image so you can see the high frequency data. So one way to think of USM is that it removes blur so you can see the existing sharpness of the image.

On the other hand - High Pass removes low frequency data and only passes through higher frequencies (second derivative or Laplacian). When we sharpen via high pass methods we are adding existing sharpness to the image.

Both methods amplify local edge contrast - in similar but different ways. USM sharpens with built in noise suppression, then when you factor in thresholding as well there is added noise control. High Pass seeks out all the noise and edges in the image and then you add them back to the original.

There are some basic steps than can be done when high pass sharpening:

* Prefilter with deskeckle or minor g/blur before high passing (less sharp but less noisy)

* High Pass and then despeckle or minor g/blur (more sharp than above but less noisy than using no noise suppression)

* Or combine both of the above methods of pre & post smoothing using smaller amounts via fades

* Desaturate the high pass blend layer after high pass filtering

* Introduce luminosity blends to the final sharpended data (see the foot of this post)

* Introduce variable halo intensity (see the foot of this post)

* Blend modes from soft light, overlay, hard light, linear light or perhaps vivid light

* Various opacity settings

* Try smaller high pass values to start and watch for halo issues as you increase size

So if noise is a concern - then USM or other methods may be better (see below). If you don't have to worry about noise or are after a little more pop - then high pass methods might be better, although the halo is different.

Then there are other filtering methods, such as laplacian of gaussian [LoG] or band pass filtering (difference of gaussians [DoG] or difference of medians, difference of box/mean etc). High pass and other methods can also be performed via adobe or third party custom filter convolution or in some cases layer or apply image blends or layers and filterings.

http://members.ozemail.com.au/~binar...volcorner.html


The above link will take you to a Photoshop action that includes DoG and DoM sharpening which is more tolerent of noise.

Sharpening can be made as simple or complex as you like.

Perhaps my biggest tip for sharpening, either using USM or High Pass or other methods is to blend the final data using the method outlined in this article:


http://members.ozemail.com.au/~binaryfx/ST_USM1.html

Sincerely,

Stephen Marsh.

[winwintoo]

Thanks Stephen - I will follow those valuable links as well.

Take care, Margaret

[Flora]

Stephen,

thanks once again for your precious tips!!!

[VG-vizualgroove]

winwintoo,
The most often overlooked aspect of image editing is how to apply edits. Edits can be either done locally or globally. A local edit only affects a specific smaller selection of an image while a global edit affects the whole image at once. To put this into perspective on using USM, here are some examples.

Often, you just want a specific part of an image to pop. Say you have a decent candid portrait with a fairly nice blurred background resulting from a shallow Depth of Field. You want the subjects eyes to really pop with maybe a little hair push yet you don't want the skin to be touched. Also, the background doesn' need any sharpening either. What to do?

Most methods, action, tutes, etc. rarely go into local editing on sharpening. Most focus on edge detection which is local editing in a manner. But if you run the action or method, it just uses all of the image and you can never get the exact desired effect. A simple solution is to use localized selections and/or masks to isolate only a particular area to sharpen. This can be copied to another layer and worked on without affecting the rest of the image. You can repeat this selection methodology throughout your image with the sky being the limit. You can make a separate layer with appropriate masking for every unique aspect of an image if you choose to do so. You then have absolute control over how your sharpening interacts with your image.

A lot of time and effort is wasted out there trying to achieve the perfect global USM technique. There ain't no such beast. Learn how to make selections and how to work interactively with channels and masks then the USM will be a piece of cake.
HTH,
VG

[winwintoo]

Thanks for the info VG, my problem with using selections is that I seem to end up with "edges" of the selections causing trouble.

I've still got a lot to learn, so I will spend some time following up on your suggestions.

Welcome to RetouchPro!

Margaret

[VG-vizualgroove]

Margaret,
Get used to using the keyboard when working on selection masks. The main keys you will use will be the D and X as well as the left [ and right ] brackets in conjunction with the shift key. The D key will select the default black and white for foreground and background respectively. The X key will switch between black and white. The bracket keys alone will vary the size up and down and when used with the shift key will also vary the hardness of the brush. By varying the hardness, size and opacity of a brush on the fly, your ability to fine tune a mask will fall into place and you will lose the harsh transitions of a typical selection.
You can also set the opacity of the brush being used on the fly with the top row of number keys. Pressing one or two keys in quick succession will allow you to customize the opacity as needed.
Regards,
VG

[Stephen M]

Margaret, as you say - that's the problem - when using selections for colour work and often with sharpening...they have to be very good, otherwise things tend to look fake.

This is where channel based masks are handy - as is feathering or g/blurring in QuickMask mode can help soften the transition.

http://members.ozemail.com.au/~binar...litymasks.html

Selections are one of the first things most folk learn in Photoshop, but perhaps they should not be the first thing to use in all edits. Then there are those times that nothing but a selection will do!


Stephen Marsh.