Would like a diffraction spikes filter

sebbync · **Joined:** Sep 18, 2013 **Posts:** 7

Hello everyone,

I don't know if it's the right place for feature requests. What I would like in Gimp is an efficient and easy to use filter to generate diffraction spikes (star spikes) on point lights. My particular interest is for astrophotography (those spikes are ingeneral created by reflecting telescopes, and astronomers using refracting telescopes or regular SLR lenses like to add spikes in postprocess), but I guess such a filter can be of artistic interest for other types of photographs (e.g. night shots with street lights).
The current way to do it "automatically" in Gimp ("sparkle" filter) is not straightfoward and requires a number of trial/error before finding satisfactory results. Plus, it gives additional spikes that one cannot remove (i.e. choosing 4 spikes gives 4 additional shorter spikes).
I don't know of other ways to do it with the Gimp (it is possible to use a custom brush, but then one need to adap manually the size and color of the brush to intensity and color of the light source).

Would it be possible to develop this kind of filter in G'MIC?

Acmespace · **Joined:** Aug 30, 2013 **Posts:** 63

I've followed this tutorial with good results: http://www.scottphotographics.com/makin ... t-in-gimp/

4 points and you control the length and angle of each point.

This might be a process a knowledgeable person (which I am sadly not) could automate in G'MIC (hint) or write a script for (hint). :coolthup

Graechan · **Posted:** Fri Jan 23, 2015 12:18 am **(#3)**

I'd be happy to create a script for this if I could get hold of an image to test on, preferably the original of this

paynekj · **Posted:** Fri Jan 23, 2015 2:20 am **(#4)**

Graechan wrote:

I'd be happy to create a script for this if I could get hold of an image to test on, preferably the original of this

You could try my "before" picture from the recent thread about starburst filters: viewtopic.php?f=9&t=11654#p157795

Kevin

Graechan · **Posted:** Fri Jan 23, 2015 6:37 pm **(#5)**

Results from my 'Star Effect Filter'
original Image

result

Charlie · **Joined:** Nov 15, 2014 **Posts:** 161

That's a really nice effect Graechan. Where can that filter be found?

Graechan · **Posted:** Fri Jan 23, 2015 10:12 pm **(#7)**

Charlie That soft effect script has already been posted but a sharper affect has been done as well as below

Adventure · **Posted:** Sat Jan 24, 2015 12:12 am **(#8)**

Graechan wrote:

Results from my 'Star Effect Filter'
original Image
[ Image ]
result
[ Image ]

I like the two pictures. Kinda reminds me of San Antonio in my opinion.

Graechan · **Posted:** Sat Jan 24, 2015 12:42 am **(#9)**

Adventure that's not San Antonio that's Sydney Australia

Iain · **Joined:** Feb 13, 2013 **Posts:** 86

I made a filter in G'MIC for this. iain_star_burst is in Testing -> Iain Fergusson

Graechan · **Posted:** Sat Jan 24, 2015 8:31 pm **(#11)**

Very nice filter Ian :coolthup

Odinbc · **Posted:** Sat Jan 24, 2015 9:46 pm **(#12)**

Thank you Ian. :bigthup

Default except Intensity: 1.50

Original photo by melschmitz

sebbync · **Joined:** Sep 18, 2013 **Posts:** 7

Ian, you did a great job. The result is close to what I'd expect.
But in your filter, the spikes' radius is fixed, would it be possible to have the radius vary according to the light intensity of the detected stars?

Iain · **Joined:** Feb 13, 2013 **Posts:** 86

sebbync wrote:

Ian, you did a great job. The result is close to what I'd expect.
But in your filter, the spikes' radius is fixed, would it be possible to have the radius vary according to the light intensity of the detected stars?

I can't think of a way to incorporate it into the filter easily.

sebbync · **Joined:** Sep 18, 2013 **Posts:** 7

Thanks Ian