Hi all,

I'm new to Inkscape, and I'm hoping I can use it to achieve an effect I'm looking for...

I'd like to create an image which carries a single scribbled path. Not too hard, except that I'd like the brightness of the path to vary along the path in a time-regular way. In other words, I'd like to essentially define a function which is a periodic variation of brightness with respect to time, and then paint with it. The result will be that if I move the mouse (or pen) slowly, the variations in brightness will be closely bunched together, and they'll spread out more if I move the mouse or pen rapidly. I've tried this in the GIMP and Photoshop, but the periodic dynamic brushes in those applications are distance-dependent, which means that no matter how fast I move the pen, the pattern remains constant with respect to pixels traversed.

The brightness function I want to use, by the way, is here: http://www.eso.org/public/archives/images/screen/eso9948i.jpg

It's the apparent intensity of the Crab pulsar as seen from Earth. Notice that its cycle has two peaks of brightness: a brighter one and a dimmer one. So, essentially, I'm looking to create an image which would look like I was erratically waving a camera around when taking a long exposure picture of the Crab pulsar. (Or erratically waving the Crab pulsar around, I suppose! )

Why would I want that? Answer: I'm writing a book. (I have sometimes wondered about simply saying "It's OK, I'm writing a book" when I'm up to anything a little strange. )

So then, to summarize the requirements:

* A black background

* A time-dependent white brush which follows a repeating cycle of the brightness pattern in that diagram; and maybe also modulates the brush diameter a little with brightness, to emulate the behaviour of the human eye (and cameras).

Think Inkscape can help me with this?

Thanks!
Dan

Short answer : no. You can't change brightness, color or size along a svg path.

Middle answer : if you draw a simple line you can to some extent emulate brightness or color variation by using a gradient.

Long answer : you can split your path into subpath and then tweak the size, color, brightness of those subpaths.

So, to sum up,
No, current version of inkscape can't help you (I'm afraid)

Maybe more luck with http://mypaint.intilinux.com/ ?
It has way more options for brushes than gimp.
But I'm not sure for time dependent brush.

foxcorner wrote: I've tried this in the GIMP and Photoshop, but the periodic dynamic brushes in those applications are distance-dependent, which means that no matter how fast I move the pen, the pattern remains constant with respect to pixels traversed.

Have you tried, in the mapping matrix in GIMP, linking velocity to spacing and/or rate and/or opacity?

Something similar can be achieved in Inkscape with the calligraphy tool to make a width dependent on velocity stroke and then using the tiled clones to 'trace' that path with many objects of the same size but brightness varying according to the stroke underneath, but vector is not the right tool for this IMO.

Thanks for the replies, and especially the mapping matrix in the GIMP. I'll look at that. If that fails, I think I'll have to brush off my C skills and write some OpenGL code...

v1nce wrote:Maybe more luck with http://mypaint.intilinux.com/ ?
It has way more options for brushes than gimp.
But I'm not sure for time dependent brush.

Wow - MyPaint is amazing! The brush options are almost endless,
and all sorts of things - including speed - can modulate other parameters.
This might be what I'm looking for! As long as I can figure out how to
emulate the brightness graph, I'll get what I want!

Thanks for the pointer!

Dan