Re: [Gegl-developer] Converting Plug-ins from GIMP (despeckle)

[Michael Natterer <mitch gimp org>]

On Mon, 2016-07-18 at 15:39 -0700, Gregg Hauser wrote:
> I'm considering converting existing GIMP plug-ins to use GEGL,
> looking 
> initially at  despeckle.c

Hi Greg,

that's great news, new contributors are very welcome :)

> The algorithm changes the source buffer if "Recursive" mode is
> chosen.
>
> Question: Is changing the source buffer returned by gegl_buffer_get 
> acceptable?

This plug-in falls in the "filter" category and you would get
rid of the GIMP plug-in alltogether and write a GEGL op, which
will then gets its GIMP GUI auto-generated. This is also the
much easier approach, you can simply port such filters to float,
drop the GUI and done.

> Request for Comments: The basic algorithm in GIMP's despleckle
> chooses a 
> pixel randomly from those pixels closest to the median in luminance, 
> avoiding pixels above and below user specified levels of luminance. 
> Colors may change as long as the luminance of the pixel chosen is
> close 
> to median around the pixel being calculated. This seems like a
> disaster 
> to me. The 3 channel median-blur.c algorithm in gegl/workshop seems
> a 
> lot closer to what this plug-in should be than the original code in 
> GIMP. The literature is full of other despeckle algorithms, some of 
> which preserve detail better than the median technique. Some
> despeckle 
> algorithms are appropriate for black and white images only.

I'm not the master of algorithms here, maybe somebody else can answer
that question...

> Question: Does the 2.10 or 3.00 version of GIMP need to slavishly
> mimic 
> the existing plug-ins?

It is preferred, unless the GIMP plug-in code is broken or otherwise
totally shitty. We'd like to auto-redirect scripts calling the
plug-in to the new GEGL op, and that works best if they do exactly
the same. It's not a strict rule tho and probably mostly depends on
you own judgement, because having looked into the issue makes you
the foremost expert on despeckle :) (GIMP plug-ins don't get a lot
of attention usually).

Regards,
--Mitch