Another Way to Sharpen an Image

Some editors allow one to sharpen an image several times, one on top of the other, e.g. FastStone Viewer or the GIMP but not RawTherapee.

With several overlaid steps of USM sharpening, it is possible to avoid halos for a greater degree of sharpness.

Original:

Then apply three or more steps of USM, e.g. in FastStone:

1,7px, amount 13
0.7px, amount 17
0.3px, amount 29

Voila:

Open both in separate tabs and click back and forth ...

Sorry, not understanding this one.
That, is a crunchy mess.
What are you viewing these on, a phone ?

Unfortunately, when I look again, the original image has halos which were exaggerated by the method because I overdid it for illustration.

I am aware of other methods.

Apple Watch 😉

Reason explained above.

Tried again:

Before #2

'Before' image is not intended for critiquing (color cast, lightness, composition, etc.).

After #2

Because they are made up of a series finite dots sharpness in images is apparent and dependent on viewing distance. Take a magnifying glass to the image on your screen and you will see that it behaves quite differently to taking a glass to a real tractor. On a screen the tractor loses the impression of detail and sharpness, it disappears as the true nature of your computer screen becomes visible. Move away and the impression of detail and sharpness reappears. So sharpness isn't absolute, it changes in relation to your viewing distance, it's apparent and an illusion achieved only when you view from a set distance or behind.

Sharpening tools don't sharpen images, they create the illusion of sharpness by increasing the acutance across the higher contrast boundaries. They tend one side towards black and the other towards white, hence the halo. Whether you do this in one go or many if you increase the "sharpness" you increase the contrast on the boundary and so produce the same halo of white against the black. And chew detail in achieving this.

View over-sharpened images at closer distances and that detail and apparent sharpness disappears, stand even further back and the sharpness reappears.

If you want sharpness, realise that it's only "apparent", an illusion in images and stand back. Lean into the screen or print and it will disappear again.

I have used this method before. Credit to xpatUSA who introduced it to this forum quite some time ago.

I found it depends on the original image how well it works - sometimes not at all.

I also found it is mostly necessary to keep the USM sum of the amount in the steps no higher than what you might use in a single step.

For example, in FastStone, my usual level of sharpening is 20 with 1.0 radius. This generally works ok but if there is plenty of sunlight I need to check that any specular highlights haven't blown up or that any small light areas look too bright. I also check things like feathers as they will often look like they have had hot wax combed through them.
So every now and then I might need to reduce the amount to 15 and maybe 0.7 radius and occasionally even less - at that point it generally means I have a pretty crappy image to start with and there would have to be something else about the image to entice me to continue.

Sometimes multiple stage sharpening does help though. Lets say I have a bird whose feathers are not standing up too well even with 15 and 0.7 but I do want to sharpen the image.
There are times when say amount 7 at 0.5 radius, 7 at 0.7 and then 7 at 1.0 might help. It is not a given and needs experimentation with the radius values. But in general, if the amounts add up to greater than what I would normally use, it will be at best the same and otherwise worse than a single stage.

So, do you Gents save the JPEG at each sharpening, or do you keep revisiting the sharpening tool for each variant prior to a final save ?

You have to save the jpg after each step... Obviously not the same as editing a raw unless you went to tiff or other

Hmmm, looks like you only get 5 goes at it, at best.
How that applies to nuances at the edges is going to depend on your choices, I reckon.

Before anyone looks for it, this was handy.
fstoppers.com/education/about-jpeg-images-and-their-quality-degradation-435235

8 bit sRGB doesn't sound like an optimum way of sharpening, also have to be aware of default settings such as sharpening and noise reduction when opening again.

Couple of points.

If you view two images in succession with the human eye then your eye will key on on the differences, it will not see either as absolute quantities but it will see the "relative" difference. If you want to see an image then you will have to view it in isolation for at least 30 seconds. I could add a third, hideously over sharpened, example and it would make the second seem softer. For a short while...

Sharpening in images is still an illusion, you don't actually sharpen but instead trick the eye. And like all tricks it doesn't stand close scrutiny, my over sharpened example would fail the 30 second viewing.

And there is the key to sharpening, in those two statements. Actual sharpness and detail come at the point of capture only, in terms of editing sharpness is relative and apparent only. If you want to make something look sharper then you could just as easily contrast it against a softer background, this is essentially how flicking between the two images above works (see below). In images you also have to go with "consistent with memory". We expect high acutance subjects to look sharper, like eyes against softer cheeks, smooth reflections on water, highly polished cars, etc. If you go against this then you kill the illusion, if the eye is slightly softer than the nose then your initial impression is soft no matter how much you sharpen. Get it the other way round and it's instantly much sharper without even touching the USM. Also applying a global USM and equalising the differences can destroy the illusion as a universal level of apparent sharpness is not consistent with our memory, it looks fake.

(combine the foreground of one with the background of the other in a single shot and you create the effect of flicking between the two in a single image, do you think you might even be able to tone the sharpening down a little more and still create the same effect?)

I like this effect, in landscape it can create the closest illusion to actual sunlight.

My preferred method in Ps has always been the High Pass Method. Being on a separate layer it can be masked and so applied locally and with a gradient. Besides, sharpness is not the only quality of images.

Which Coo has the softer and finer coat?

Local High Pass:

Universal USM:

Every time you re-save JPEG, it looses IQ. Saving same JPEG files 5 times...

I do not save at each step. I can also apply the method to any format supported by FastStone or GIMP, not just JPEG, with an unlimited number of steps.

In the GIMP, I'm 32-bit floating-point Linear for all editing. FastStone - not sure.