Question about the fuzziness slider in the color range tool

[Jeffrey Saldinger]

I am aware that when the fuzziness is set to 0%, the selection has hard edges

at 82 and 164 (for the example shown), and as the fuzziness setting is increased,

the range of the image’s tones over which the selection goes from 100% selected

(white) to 0% selected (black) increases.

My question is: What does the slider measure a percentage of, exactly?  Or, to put

it another way, for a given setting of the fuzziness slider (e.g. 33%, 67%, or 100%),

how can I know the image’s tones that are the “first” (on either side of the range

setting) to be 100% unselected?

Thanks

Jeffrey Saldinger

[Trevor.Dennis]

You can't beat gradients when it comes to working this sort of thing out. So with Fuzziness set to zero we see the vertical line we expect

Just moving the Fuzziness slider to the right shows how far the selection extends, but does the number relate to anything?

To work that out, you need a reference point for the initial selection, so drag out a guide and make that your initial selection point. It's actually a bit tricky, and you have to sort of sneak up on it got the zero Fuzziness point right on the guide.

Increase Fuzziness to something like 50, and OK it.  You can then measure RGB values for the extent of the selection

In this case the difference is 31 above and below our references, but the marching ants indicate the 50% point.

We can show the full extent of the selection using Quick Mask.  I have set the QM colour to blue to avoid confusion, and turned off the red/black gradient.

If we drag out guides to the now revealed selection extent, and measure the red content at those locations, we find that the differences are now very close to the value at our initial selection (255 - 206 = 49 and 206 - 147 = 59)  Not perfect, but this was a very much a by eye experiment, so probably close enough to use as a guide.

I am personally very happy to take a 'black box' approach to this sort of thing, and only get pedantic if it is going to help me use the product — but it was an interesting exercise all the same. 

[Jeffrey Saldinger]

Thank you, Trevor, for spending the time to prepare this reply.

As I understand what you’ve shown, your method would provide

the answer to my original question for any single given situation,

although somewhat painstakingly.

But what I had in mind as a possible answer was something actually

calculable (and more or less readily) from the settings in play (e.g. in

my example above, midtones between 82 and 164 with whatever

fuzziness is selected).

So perhaps another respondent will have something to add.

I realize now that perhaps I should have added in my OP that my

interest is in making selections of BW photographs to use for making

layer masks for certain effects.  I gather that in a color image, the

different channels might fall into 100% unselected at different distances

from the given 100% selected range.

Thanks again.

Jeffrey