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Remove pixels next to a particular color
Posted: 2014-04-28T10:44:05-07:00
by cookmeplox
I have a bunch of icons that look something like
this. I would like to remove any pixels that are the color #212121, that are also 8-connected (directly north, south, east, west, north-west, south-west, north-east or south-east) to any pixels that are either #080808 or #070707. It would look like
this afterwards. Generally, I want to remove pixels if they are a certain color, and are touching pixels of another certain color. I've looked a bit into morphology, but I haven't figured out how to also add the color-related rules.
Re: Remove pixels next to a particular color
Posted: 2014-04-28T11:20:42-07:00
by snibgo
Pixels can't be "removed". Perhaps you mean "make transparent".
This is a complex problem, but not difficult if you break it down into sub-problems. What have you done so far? Have you broken it down? What parts are giving you problems?
Re: Remove pixels next to a particular color
Posted: 2014-04-28T12:10:43-07:00
by cookmeplox
Sorry, yes, I am referring to making those pixels transparent. I'm really not sure how to approach the problem -- the images are small enough that I could just go pixel by pixel. Or perhaps I could list all pixels that are neighboring the #080808/#070707 pixels somehow, and then see how many of those are #212121...I'm really not sure.
Re: Remove pixels next to a particular color
Posted: 2014-04-28T12:46:15-07:00
by snibgo
I would break it down like this:
We need to make some pixels transparent. Which pixels? Only those that are (a) #212121 and (b) 8-connected to a pixel that is either #080808 or #070707. All other pixels must retain their existing transparency.
"Doing some action to some set of pixels" is often done with a mask. I'll use the convention that white means the pixel is in the set, or black means outside the set.
We can easily find the set of pixels that are a certain colour, eg #212121 or #080808, or are already transparent, or whatever.
As you have realised, "-morphology" can find adjacency. "Square:1" finds 8-connected adjacency.
Then it's just a question of combining sets of pixels. Making the result the lightest from a pair of images is equivalent to finding pixels that satisfy EITHER condition 1 OR condition 2. Making the result the
darkest is equivalent to finding pixels that satisfy BOTH condition 1
AND condition 2
Combining these thoughts gives the following Windows BAT script. Adjust for other languages. Don't worry about %IM%; that's just for my computer. The commands could be rolled together into single command with no intermediate files. The result is n6.png, which is identical to your desired result.
Code: Select all
rem What pixels are either #080808 or #070707?
%IM%convert ^
P6Cl54N.png ^
-background Black -flatten ^
-fill Black -opaque White ^
( -clone 0 -fill Black +opaque #080808 -fill White -opaque #080808 ) ^
( -clone 0 -fill Black +opaque #070707 -fill White -opaque #070707 ) ^
-delete 0 ^
-compose Lighten -composite ^
n.png
rem What pixels are adjacent to pixels that are either #080808 or #070707, or are those pixels?
%IM%convert ^
n.png ^
-morphology Dilate Square:1 ^
n1.png
rem What pixels are #212121?
%IM%convert ^
P6Cl54N.png ^
-background Black -flatten ^
-fill Black +opaque #212121 -fill White -opaque #212121 ^
n2.png
rem What pixels are #21212 AND adjacent to pixels that are either #080808 or #070707?
rem These need to be made transparent.
%IM%convert ^
n1.png ^
n2.png ^
-compose Darken -composite ^
n3.png
rem What pixels are already transparent?
%IM%convert ^
P6Cl54N.png ^
-alpha Extract ^
-negate ^
n4.png
rem What pixels need to be made transparent OR are already transparent?
%IM%convert ^
n3.png ^
n4.png ^
-compose Lighten -composite ^
n5.png
rem Make the correct pixels transparent.
%IM%convert ^
P6Cl54N.png ^
( n5.png -negate ) ^
-compose CopyOpacity -composite ^
n6.png
Re: Remove pixels next to a particular color
Posted: 2014-04-30T14:15:46-07:00
by cookmeplox
Thank you very much! That's exactly what I was looking for. For future reference, is it possible to do this kind of thing without actually saving all the temporary files?
Re: Remove pixels next to a particular color
Posted: 2014-05-01T00:00:35-07:00
by snibgo
Yes. The commands could be rolled together into single command with no intermediate files. That would make it much faster.
When I'm trying to solve complex image processing problem, I break it down into stages, solve each stage as a single command, and put them in a script. When I've tested it for a while and I am convinced it works, I combine the commands and eliminate intermediate files.
Try combining them yourself. Just do one at a time. For example, n.png is used only to create n1.png. You can easily combine these two commands together, so it doesn't create n.png.
