Sharpening filters

[dkj]

How do the Clarity, Unsharp Mask, and High Pass filters differ from one another? And how do they differ from the Detail Refinement adjustments in the Develop persona? I'd like to find out how the different algorithms work.

[James Ritson]

Hi djk, here's a brief rundown of each filter:

 

Unsharp Mask uses the traditional approach of comparing and subtracting a blurred (or "unsharp") version of the image (or pixel layer). It's the most configurable of the sharpening filters as you can control the factor (strength) and threshold (how much to subtract based on the comparison). For most use cases, this is your go-to filter for sharpening.

 

High Pass is a little more straightforward: it simply passes parts of the image (or signal) above a certain frequency and attenuates anything below it. This filter is used as part of Photo's automated Frequency Separation filter for retouching, but you can also use it for detail enhancement. Applying it as a Live Filter layer then altering its blend mode (e.g. to Overlay/Hard Light) allows you to be somewhat creative with your sharpening: use smaller radius values for fine detail sharpening and higher radius values for local contrast enhancement.

 

Clarity has had an overhaul in the Develop Persona, so it now behaves differently compared to its implementation in the Photo Persona. In Develop, it performs quite a strong local contrast enhancement (punchy mid-tones, increase in "perceptual" sharpness). In Photo as a filter/live filter, it's basically Unsharp Mask with a blend mode - or at least it should be. As of the latest release version, it no longer appears to be any different from Unsharp Mask, which is a bug and will be reported...

 

Detail Refinement in Develop is basically Unsharp Mask - the percentage suggests it might be adaptive but I don't believe this is the case, just treat it as the radius.

 

Hope that helps!

[R C-R]

1 hour ago, James Ritson said:

In Photo as a filter/live filter, it's basically Unsharp Mask with a blend mode - or at least it should be. As of the latest release version, it no longer appears to be any different from Unsharp Mask, which is a bug and will be reported...

Could you explain a bit more about that? I seem to be getting different results using Unsharp Mask vs. Clarity, but I don't know what blend mode, factor, etc. would be appropriate for the comparison.

[James Ritson]

On 04/04/2018 at 11:30 AM, R C-R said:

Could you explain a bit more about that? I seem to be getting different results using Unsharp Mask vs. Clarity, but I don't know what blend mode, factor, etc. would be appropriate for the comparison.

 

Just to expand on this, there does appear to be a slight difference. Clarity has basically always been USM with a Luminosity blend mode (at least in the Photo Persona). The test imagery I was using, however, showed little to no change. I've tried some other images and there is a slight difference, but from memory of previous versions (1.4, 1.5) I was expecting a bigger difference.

 

Applying a live USM layer and setting its blend mode to luminosity should yield the same result as Clarity. The eventual hope is that the Photo persona version will behave like it does in Develop, where you get less edge haloing and the ability to apply it negatively.