On 03/16/2011 05:52 AM, Krzysztof Żelechowski wrote:

When I create a curve to apply to an image, GIMP gives me only two choices: a freehand curve and a smooth curve. I need to apply a stepping curve (piecewise flat) and I am out of luck because there is no such option. Please help.

Originally posted at bugzilla:

_______________________________________________ Gimp-user mailing list
Gimp-user@lists.XCF.Berkeley.EDU
https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user

Not sure exactly what you want, but it is likely the pencil tool would help. It makes freehand curves or piecewise linear (using shift-click) curves.

2011/3/16 Krzysztof Żelechowski :

When I create a curve to apply to an image, GIMP gives me only two choices: a freehand curve and a smooth curve.  I need to apply a stepping curve (piecewise flat) and I am out of luck because there is no such option. Please help.

There's a function in the PDB called gimp-curves-explicit:

"Modifies the intensity mapping for one channel in the specified drawable. The drawable must be either grayscale or RGB, and the channel can be either an intensity component, or the value. The 'curve' parameter is an array of bytes which explicitly defines how each pixel value in the drawable will be modified. Use the 'gimp-curves-spline' function to modify intensity levels with Catmull Rom splines."

So I guess it would theoretically be possible to write a script or plug-in for this.

Chris

On Thu, Mar 17, 2011 at 2:28 AM, Křištof Želechovski wrote:

Thank you.  This means it is unsupported (for the end user).  Could you be so kind and reopen my bug, or at least place a comment to that effect?

Can you provide an example of the type of curve you wish to apply?

I'm not sure what would be best - maybe a quick Inkscape drawing, a series of points or something else?

Chris

Chris Mohler wrote:

On Thu, Mar 17, 2011 at 2:28 AM, Křištof Želechovski wrote:

Thank you. This means it is unsupported (for the end user). Could you be so kind and reopen my bug, or at least place a comment to that effect?

Can you provide an example of the type of curve you wish to apply?

I'm not sure what would be best - maybe a quick Inkscape drawing, a series of points or something else?

Turn ccw:

│
│
└───┐
│
│
└──┐
│
│
│
└─┐

Chris

I think you will have to fake it. Draw the curve and keep it as a path. Assuming you want (say) the x-axis to have equal increments, set up the grid, enable snap-to-grid, and paint constraining the line with shift for point-to-point and ctrl for angles, My attemp here http://imgur.com/8ElzN.

On Mon, Mar 21, 2011 at 1:09 PM, rich wrote:

I think you will have to fake it. Draw the curve and keep it as a path.  Assuming you want (say) the x-axis to have equal increments, set up the grid, enable snap-to-grid, and paint constraining the line with shift for point-to-point and ctrl for angles, My attemp here http://imgur.com/8ElzN.

We're talking about using straight line segments in the Curves tool (not the Bezier tool - we're not talking about paths).

I still haven't thought up an easy solution.

Chris

I still haven't thought up an easy solution.

Chris

If you export the curve to a file you can ee the syntax used, then create your own files that can be loaded into the curve tool.

-Rob A>

I still haven't thought up an easy solution.

Chris

If you export the curve to a file you can ee the syntax used, then create your own files that can be loaded into the curve tool.

-Rob A>

That was roughly what I was thinking as well, develop an algorithm that will write a 'block'.

Here is one that I did as an experiment 'by hand' (well by spreadsheet and csv)

http://www.imageno.com/j662vataf0vtpic.html

I still haven't thought up an easy solution.

Chris

If you export the curve to a file you can ee the syntax used, then create your own files that can be loaded into the curve tool.

-Rob A>

That was roughly what I was thinking as well, develop an algorithm that will write a 'block'.

Here is one that I did as an experiment 'by hand' (well by spreadsheet and csv)

http://www.imageno.com/j662vataf0vtpic.html

Hi all,

On Mon, Mar 21, 2011 at 7:09 PM, rich wrote:

I think you will have to fake it. Draw the curve and keep it as a path.  Assuming you want (say) the x-axis to have equal increments, set up the grid, enable snap-to-grid, and paint constraining the line with shift for point-to-point and ctrl for angles

... here's how to use the path as specification for a curves-alike color mapping:

0. Install Rob Antonishen's "Sample Gradient along Path" Script [1]

1. Create image 256x256 pixels 2. Draw gradient black to white from bottom to top 3. Create the desired curve as a path 4. Create a new gradient via "sample gradient along path" - with 256 steps and
- sample radius = 1
5. Switch to target image
6. Apply Colors->Map->Gradient Map

not for the faint of heart...

regards, peter

[1] http://ffaat.pointclark.net/blog/archives/155-GIMP-Script-Sample-a-Gradient-along-a-Path.html

Krzysztof Żelechowski (giecrilj@stegny.2a.pl) wrote:

When I create a curve to apply to an image, GIMP gives me only two choices: a freehand curve and a smooth curve. I need to apply a stepping curve (piecewise flat) and I am out of luck because there is no such option.

It should be reasonably easy to implement a new curve type that implements this kind of piecewise constant function. One starting point for this could be the function gimp_curve_calculate() in app/core/gimpcurve.c.

IMHO also interesting would be a piecewise linear type that connects the control points with straight lines.

Bye, Simon