Narrow Band Mask

[Simon Hicks]

Hi PI Guys,
                    I recently did some processing using PI and I had some very faint nebulocity that I wanted to pick out and selectively process in a very different way to the background and to the brighter parts of the image. It was  very very close to the background in terms of brightness, but different in terms of structure from the background.

I therefore created a luminance mask and used the Curves module to create a very narrow band filter by putting a node somewhere on the line, and then dragging the line down to zero on either side of the line.

By moving this line around and looking at the preview I could eventually select out the features I wanted. I could even change the bandwidth by adding a couple of extra nodes and 'fattening' out the spike.

This is quite laborious with curves because you have to keep moving individual nodes around...maybe five or more nodes. It would be much easier if there was a way of simply specifying the centre and bandwidth of the filter...and maybe even being able to just slide the centre around and see the effect on a preview.

Now if I'm the only person in the world that is asking for this, then hey, I'll do it by moving nodes around. And I'm not even sure it is something I would use very often.....so I'm definitely not screaming out for it, if you get my drift.

I've really just raised it as something of interest, and if there's loads of others that would use it, then maybe it could become a feature suggestion.

An alternative could be that you could specify the centre by clicking the mouse on the part of the image you are trying to select?

Cheers
             Simon

[David Serrano]

Another approach to this would be to be able to select several nodes at once (for example, by pressing Ctrl while clicking on them), so all of them could be dragged at once.

[Simon Hicks]

Hi David,
                 That's a good idea that would certainly work for me. And my guess is it would be easier to impliment this into the existing Curves module than creating a new module from scratch. Good and efficient.

 

Cheers
             Simon

[Juan Conejero]

Hi Simon, David,

As David, I think the best solution is to allow multiple point selections in the CurvesTransform interface. In this way all selected points could be moved or deleted in a single operation. Thanks to both for an excellent suggestion!

[David Serrano]

Let's push a bit more then :twisted:.

What about not selecting individual nodes with Ctrl-click, but selecting the ones that fall inside a rectangle? Like selecting process icons in the desktop.</kidding>

[Juan Conejero]

Let's push a bit more then

David, ya te echaba de menos  

Then there's another nicety that comes to my mind. Have you seen the ColorSaturation interface? How about some sort of a shift parameter in CurvesTransform to move all points horizontally? OK, hue is a circular angular quantity (0deg = 360deg) while curve points are constrained to [0,1] and cannot circulate, so both problems are radically different. But the idea sounds interesting, doesn't it?

[David Serrano]

CT has a Hue curve, which could benefit from this. I definitely support the idea (although I feel that the "right" approach to this issue is the ability to select multiple nodes).