Re: [Gimp-user] why no difference of gaussians on layer masks? gimp 2.7.5

Hi Gary,

edge_dog isn't the most elegant of plug-ins, and behaves more like a script than most C plug-ins; it creates temporary layers, and to do so, uses gimp_layer_copy.  (see line 471).  So it inserts a check that the drawable is a layer before it does anything else. 

I expect that careful checks and alternate code paths could alleviate the issue (copying masks to new layers), or it could be rewritten to do its operations in a more self-contained way.  I'm not volunteering here, but it doesn't seem like an insurmountable amount of work for someone motivated.


Seth Burgess

On Sat, Jan 21, 2012 at 3:20 PM, Gary Aitken <gimp dreamchaser org> wrote:
Hi Alexandre,

Yes, I'm aware that I can work around it as you mention, and have been doing so.  But it is a pain in the rear, and unless there is some over-riding reason for not allowing one to do this operation, it seems the gimp should allow it.

My main reason for posting was to see if it is a known issue and decided to be left as-is.  I don't see an open bug for it.  I suspect it may be a relic of implementation difficulties and so a capability which may be desirable but a bit awkward to implement.



On 1/21/2012 12:39 PM, Alexandre Prokoudine wrote:
On Fri, Jan 20, 2012 at 11:02 PM, Gary Aitken wrote:
Hello all,

gimp 2.7.5 on winXP, unfortunately.  New hardware problems on my freebsd
system.  grr.  Anyway...

Why won't the gimp allow me to use a difference of gaussians on a layer
mask?  This seems like a perfectly fine thing to do for edge detection, and
indeed, other edge-detect algorithms work:

For example:
 New layer mask, from grayscale copy of layer
 Filters / edge-detect / difference of gaussians says:
   Execution error for 'Difference of Gaussians':
   Can operate on layers only (but was called on channel or mask).
 Filters / edge-detect / Edge...
   works fine

Is this a bug, or am I missing something?
Any insights would be appreciated,

Hi Gary,

Not sure about the technical side of this, but you should be able to
perfectly work around that.

1. Enable display of the mask via right-click menu so that the mask is
displayed instead of the layers's contents.
2. Layers>  New from Visible.
3. Apply your filter to that layer.
4. Copy all of the layer's contents and paste it into the mask.
5. Remove or disable the extra layer you created.

Alexandre Prokoudine
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