Local sharpening and Noise Reduction: Same or different effect than global?

[Hmmokthen]

Hi,

In the global settings for sharpening you have amount, radius and detail sliders (plus masking). If you want to do selective sharpening using the adjustment brush, you only have "sharpness" slider: what does "sharpness" actually mean? Is it inheriting the detail and radius settings from global and "sharpness" is the amount? Same thing for Noise reduction: you have Luminance, detail and contrast in global whereas in the adjustment brush you just have "noise".

Looking at "The Adobe LR 5 Book" by Martin Evening he writes "these effects are not all 100% comparable with the similarly named sliders in the basic panel. There are some minor differences, but otherwise they are more or less the same". Can someone please clarify if/what "sharpness" and "noise" is doing differently to the global sharpness and noise reduction. cheers

[richardplondon]

The internal workings of this are opaque to the user but I'd say that in general local settings seem to happen onto the image prior to the global ones. That is how (for example) if current global settings dictate that certain bright areas of the photo are showing featureless white, you can still recover the highlight details in these areas using local adjustments. But if you tried to recover those details  using Tone Curve, assuming global settings were being left as they were throughout, you would not find that possible. So this demonstrates a sequential dependency Local > Global > Tone Curve at least so far as tonality.

Clearly the idea of global adjustments is that they will continue to operate the same regardless of what you do locally. In the highlights example, the Basic panel is still operating exactly the same, but now applying onto a photo that has been strategically 'pre-darkened' in some generic way, in the necessary places - so that the result will be more as we want.

So far as these two local sliders it is harder to see such sequence. They seem to me more complicated than just turning up and down the 'power' (strength of effect) of whatever the corresponding sliders in the Detail panel are doing, especially when it comes to the more extreme settings (towards +100 or towards -100).

Setting a high value for local Noise seems to pre-blur the image (not to make it more noisy), while a low value does nothing apparent, when you have zero global NR applied. OTOH setting a high value for local Noise seems to do nothing, and a low value seems to disable global NR or at least to counteract it, when you have a lot of global NR applied. So this slider's naming is a little non-obvious too IMO.

The main Detail panel is where we judge and adjust with the most control, what we are going to do about such noise, and about such detail, as appears post local adjustments in processing terms. Always across the whole image, and in a unified way aesthetically speaking, for the entire photo. But in our practical working sequence we will first see what the global NR and sharpening are doing and only then can we judge what if any local NR or sharpening tweaks are pictorially called for, in response to that. 

Taking the analogy of film or paper grain, that does not (cannot) be varied in itself across different parts of a traditional process. But perhaps one can have modified the focus or changed the exposure selectively for certain parts of the photo such that this physical grain is then responding to, and therefore representing, different 'input' than it otherwise would have done.

[Ian Lyons]

I was the Tech Editor for all of Martin's Lightroom books and recall that he spent a considerable amount of time and effort coming up with a method for demonstrating how each of the controls interact. Sadly, he passed away late last year. However, I believe the image he used in the book is still available at www.thelightroombook.com, although you'll need to register. Whether you do or don't manage to obtain a copy of the image, I would encourage you to check out the slider interactions.

Answering your questions.

Yes, the 'Radius', 'Detail' and 'Masking' sliders in the global 'Detail' panel are used by local 'sharpening'. Martin explains on page 402 of the book you referred to as to how positive values for the local 'Sharpeness' slider  are additive with the global 'Amount'  slider(i.e. 45 local plus 100 global = 145 local).  As Martin explains on Page 404 the same principal does not apply when negative values of -50 to - 100 are applied to the local 'Sharpeness' slider. That is from local 0 to -50, the global sharpening affect is reduced, at -50 it's disabled, and from -50 to -100 it becomes a blur tool. This is best seen by setting the local 'sharpness'  to say -60, then dragging the global 'Amount' slider from miunimum to maximum and vice versa.

For the most part, global and local noise reduction work in much the same way as sharpening (i.e. global 'Detail' and 'Contrast' sliders used for both global and local). The key difference being that the global 'Luminance' slider affect is not disabled when the local 'Noise' slider reaches -50. Therefore, in areas with  a value of say +50 global 'Luminance' and -50 local 'Noise', the two should cancel each other out.