Threshold

[Robert Schleif]

Quite a few transformations use a threshold. For some, e.g.. Paint tool, Flood fill, Advanced sharpen noise reduction ..., the affected pixels are less than the threshold setting. That is, moving the threshold slider to the right increases the amount of the image affected. For other transformations, e.g. Sharpen, Pinhole, Unsharp mask..., the affected pixels are greater than the threshold setting and moving the threshold slider to the right decreases the decreases the amount of the image affected. I can't remember which way each transformation works and it is a distraction from my focus on the image itself to try to deduce the behavior logically. Thus, I end up diddling around a bit. For me it would be a significant aid if the threshold scale had a way of indicating whether the active portion of the scale lies to the left or to the right of the slider. One way that would work for me is to have the active region on the threshold scale in white rather than gray throughout.

[jsachs]

Another way to tell which is the active end of the threshold slider is to set the default value consistently so that when the transformation comes up the slider starts out at or near the end where the slider does nothing, and as you move it toward the other end, its effect increases gradually. This is generally what I have tried to do with the built-in defaults, although it's possible I may have gotten one or two of them wrong.

Also there are threshold sliders (e.g. Sharpen) and threshold scales with markers and a gray bar to indicate thresholds that take effect over a range of values (e.g. Advanced Sharpen and the Mask Texture tool), and these display differently.

[Robert Schleif]

Starting the threshold slider at the position where the transformation would do nothing seems OK, although it would be good to emphasize this in the documentation. Intuitively however, if the transformation's slider begins at the far right, it is counterintuitive on its own that moving it to the left will increase the effect of the transformation. The more clues that can be built into the interface, the better it would be. The use of white to indicate an active range would be similar to its use in the Color Range Tool in the mask operation.
Would it be too confusing if the threshold scale were reversed for those transformations for which the active area currently is to the right of the slider? Then the default position of the slider in all cases could be on the far left, and moving it to the right would increase the effect of the transformation.

[tomczak]

I can't think of an easy sollution to indicate which side of some thresholds is the inclusive one and which is the exclusive, but I have to admit that I have to think quite hard and/or experiment with them a little every time I use them. The ones with the gray-bar scales like AS or Mask Colour Range are easy - the regular ones are those that are not that easy to figure out quickly.

This probably won't work, but the sliders' scale on top of which the slider is moving, is it a static image, or perhaps it could be greyed out (or made white as Robert suggested) on exclusive side of the slider position?

In a similar vein, sliders have dynamic percentage displays above them indicating current slider position - perhaps this display can be embellished with some kind of intuitive indicator (eg. full circle/empty circle or X/checkmark or some similar pair of characters) that would show if the slider moves towards the inclusive or exclusive end?

[jsachs]

I have reviewed all the transformations I could find that use thresholds, and the only ones I could find that work backwards are all the ones related to blurring. I could make these sliders run the other way. Are there any others that you think should be reversed?

[tomczak]

Would that pass for a definition of threshold: a value at or above which some changes happen, but not below it?

i.e. at threshold 0% everything happens, at 100% nothing happens?

[jsachs]

Your definition is fine, but at least some of the confusion is what everything and nothing mean: is it that the transformation does nothing or that the threshold does nothing.

My suggestion for sliders is to make the threshold do nothing (i.e. make the transformation do everything) when set all the way to the left and to do everything (i.e. make the transformation do nothing) when it is set to the right, so the threshold progressively limits the action of the transformation (or mask tool) as you move it from left to right. This means reversing the blur sliders and a few others while leaving the sharpen sliders and a few others the way they are.

Here are the transformations and tools that I have identified that I think need to be reversed from their current direction:

Advanced Sharpen (Speck Removal tab)
Blur, Gaussian Blur
Precise Gaussian Blur
Watercolor
Mask Median and Pinhole tools

If you think I am missing any, let me know.

[tomczak]

Good point. So the winning entry will be that the threshold value of 0% will mean that the there is no threshold for the transformation to proceed (i.e. the threshold does nothing, as if it wasn't there, hence 0%)?

[jsachs]

I was not planning on changing the % values, just the direction of the slider. If I change the %, I have to change all the documentation and manuals.

[tomczak]

Would that mean that the labeling of the threshold sliders' ends would change? So for instance, if the left end of some of the sliders was zero, it would become 100% and vice versa? The meaning of percentages would stay the same for each respective transformation - ditto, no need to change documentation?

In which case the direction from left to right will be the mental help in remembering that the left side would not affect the transformation at all, and the right side would prevent the transformation from happening?