Having read through severa other posts on this topic, it seems that capture sharpening is advised, but I'm not sure why.
Capture sharpening is essential to image quality. The capture process is inherently blurring the original signal's micro-detail contrast/resolution. One contributor to blur is the optical system, either by residual lens aberrations or by diffraction. Another contributor is the fact that sensor elements (sensels) each take an area sample of the light striking the sensor, which means that micro-detail will lose contrast. And there is often an Optical Low-Pass Filter (OLPF, or Anti-Aliasing filter) which is designed to blur the input signal. Therefore, input signal blur is a given.
The effect is demonstrated by the MTF curve of a typical camera system, which shows increasingly lower contrast modulation as detail gets closer to the limiting resolution where contrast ultimately becomes non-existing.
Capture sharpening can (up to a point) compensate for those capture process losses, and restore the original input signal strength. Who could object to that? However, the difficulty with optimal capture sharpening is that we get insufficient help from the Raw converter software to dial in the objectively correct settings. When I say 'objectively correct'
, I mean that it is possible to analytically determine
the amount and character of the blur that crippled our input signal. Once that is known, it is also possible to mathematically reverse part of that blur process.
One of the problems with Lightroom (and other Raw converters) is that the Detail tab starts with the Amount control, instead of the Radius control (which is the key to successful Capture sharpening). It also starts with the (in most cases) wrong default radius, in fact it should be trivial for the folks at Adobe to pick a better default, based on the EXIF data of the file. It appears as if they are stuck in old school thinking about sharpening.
The amount control needs to be set only after
the radius is set to the correct value, and it usually is best to set it to an amount that avoids the introduction of halos. That combination of Radius, and Amount (which may need tweaking if noise reduction is changed), should restore the original signal as much as possible without adding artifacts that will prevent high quality magnifications. That is optimal Capture sharpening in my book.
We then have the option to use a detail brush for local adjustments, and clarity and tone curves to modify the more global contrast response, but that would be more Creative sharpening than Capture sharpening. Like Output sharpening, that's a different subject.