2006.03.22 09:34, Jonathan Ryshpan rašo:

I'm trying to remove isolated black pixels in large white areas of a tiff image. The image is quite large and is black and white only.

The despeckle filter (Filters->Enhance->Despeckle) doesn't seem to do anything, except that it changes the whole image to white if the white slider is set to 256, and makes the black areas much larger is the black slider is set to -1.

Reading the documentation isn't much help -- in fact the phrase "You ought to select isolated defects before applying filter." in the help file is quite mysterious. What does it mean?

Any help would be very welcome - jon

select white area (shortcut Shift+O) then Edit>Grow>by 1 pixel and erase (Ctrl+K) or fill with background colour (shortcut Ctrl+.) Or select black area (shortcut Z) then invert selection (Ctrl+I) and erase or fill with background colour (shortcut Ctrl+.)

hi jonathan,

Selon Jonathan Ryshpan :

I'm trying to remove isolated black pixels in large white areas of a tiff image.

For this application, erode or dilate (I get them mixed up) is probably the best option. If you follow a few erodes by a few dilates, the end effect is the removal of tiny specs and detail on the bigger specs.

example:

'''''''' '''''''' '''''''' ''''''*' '''''''' '''''''' '''''*'' '''''''' '''''''' '***'*'' -> '''''''' -> ''**'''' '*****'' erode ''**'''' dilate '****''' ''**''*' '''''''' ''**'''' ''*''''' '''''''' '''''''' '''''''' '''''''' ''''''''

Reading the documentation isn't much help -- in fact the phrase "You ought to select isolated defects before applying filter." in the help file is quite mysterious. What does it mean?

just that despeckle can damage stuff which is just fine, in a photo, so selecting areas where you're interested is a good thing.

Cheers, Dave.

--
Dave Neary
Lyon, France

Jonathan Ryshpan wrote:

I'm trying to remove isolated black pixels in large white areas of a tiff image. The image is quite large and is black and white only.

The despeckle filter (Filters->Enhance->Despeckle) doesn't seem to do anything, except that it changes the whole image to white if the white slider is set to 256, and makes the black areas much larger is the black slider is set to -1.

I think you might be using the wrong tool here. I would try using a color correction curve to take out the noise. Put a node at 50% to keep your 3/4 tones and shadows safe, then take the extreme highlight point (the upper right node) 2 or 3% to the left. That should take out the noise in your white areas.

-Nate