Hello,

I just got an idea about the curve tool: Why not use it as a selection tool?

Apart from The Gimp, I do not know a lot of image manipulation programs so the feature might very well be common.

I see it like that:

A new tool called the 'curve selection' would be added probably in the Select menu.

Like the original curve tool, the 'curve selection' tool would provide several curves for the different properties of the current layer (see the list below).

The value of each curve would not provide a transformation of the property but an amount of selection (from 0.0 to 1.0) according to the property.

The result of the curve selection tool would be a selection mask obtained by multiplying the values of all curves.

For most curves, the initial value value would not be the identify function 'f(x)=x' but 'f(x)=1.0'.

The following curves could be provided: - Red , Green and Blue ( default f(x)=1.0 ) - Hue, Saturation, Value/Lightness/Brightness (default f(x)=1.0) - Initial Selection Mask ( default f(x)=x ) - Alpha (default f(x)=1.0)

With those defaults, the overall default result would be the initial selection mask.

Because of it circular nature, the Hue curve may require a specific treatment.

Hi David,

I made a file showing a typical use case:

http://www.chauveau-central.net/misc/sample.xcf

My goal here is to select the over-saturated part of the red hairs of the layer L1 as shown in L10 (a blue 'quick mask' of the final selection).

L2, L3 and L4 are simply the layers obtained by the HSV decomposition of L1. I used them to simulate the effects of the proposed 'Curve Selection Tool'.

After opening the 'Curve Selection Tool' the image would switch to a mode similar to the 'quick mask' mode showing the amount of selection at each point using a transparent coloured channel. By default, all curves would be initialized to the function f(x)=1.0 so everything would be selected by default (unless the original selection is also taken into account)

The first selection curve I would edit would be the 'Hue' as shown in 'curve1'.
The horizontal axis represents the HUE while the vertical axis represents the amount of selection according to the HUE. Here I am trying to select the red pixels so most of the curve should be set to 0% expect for the red area which should be set to 100%. After setting the Hue curve, the selection mask will be equivalent to the layer L5 which I obtained by applying curve1 to L2.

Then I would select the 'Saturation' curve and set it as shown in 'curve2' to discard the pixels with a low saturation. The effect of that saturation curve is shown in L6.

Of course, since the Hue curve is already set, the layer mask will be in fact equivalent to multiplication of L5 and L6 as shown in L5b (obtained by merging L5 and L6 in Multiply mode).

Finally, I would have to edit the 'Value' curve as shown in curve3 to discard the dark pixels.
L7 shows the effect of curve3 alone.

L8 shows the effect of the 3 curves applied together (by multiplying L5, L6 and L7).

L10 shows how the 'quick mask mode' would appear after setting the 3 curves.

David Gowers wrote:

Hi Stephane,

On Nov 20, 2007 10:10 AM, Stephane Chauveau wrote:

Hello,

I just got an idea about the curve tool: Why not use it as a selection tool?

Apart from The Gimp, I do not know a lot of image manipulation programs so the feature might very well be common.

I see it like that:

A new tool called the 'curve selection' would be added probably in the Select menu.

Like the original curve tool, the 'curve selection' tool would provide several curves for the different properties of the current layer (see the list below).

The value of each curve would not provide a transformation of the property but an amount of selection (from 0.0 to 1.0) according to the property.

The result of the curve selection tool would be a selection mask obtained by multiplying the values of all curves.

For most curves, the initial value value would not be the identify function 'f(x)=x' but 'f(x)=1.0'.

The following curves could be provided: - Red , Green and Blue ( default f(x)=1.0 ) - Hue, Saturation, Value/Lightness/Brightness (default f(x)=1.0) - Initial Selection Mask ( default f(x)=x ) - Alpha (default f(x)=1.0)

With those defaults, the overall default result would be the initial selection mask.

Because of it circular nature, the Hue curve may require a specific treatment.

I don't understand your explanation of how this would work. How about showing some example results?