Legacy ImageMagick Discussions Archive

I am trying to remove a color from an image (ie, make transparent), but along the edges of transparency create a feathered effect where it fades from transparent to opaque over the remaining colors.
The idea is to start with an image like this

and make it look like this


I've come to a dead end of ideas, the closest I have gotten is by the following: which produces:

Obviously the blurred matte has half it's gradient inside the original yellow circle so applying the matte will produce the above, which is not what I'm after.

Thanks for any help with this problem.
Jeremy

I do not know if this is what you are trying to acheive but I have used a bit of code from Anthony's examples to blend 2 images together.

An example on this page - www.rubblewebs.co.uk/imagemagick/other.php - one hard edged blend and one soft edge blend.

Thanks, that's not exactly what I was looking for though.

I found another solution to the larger problem which got around doing this at all. I didn't figure the feathering problem out, so if anyone knows I'm still interested, but it isn't necessary for me.

Use the original image to create a black and white mask, which you blured. I see you have that.

But if you want anything that is yellow to be absolutely transparent, then you need to adjust the blured mask. Blur not only leaks black (transparent) into the white, but also the white (opaque) into the black. That is why you can still see yellow color!!!!

That is at the border. you get a 50% grey in the mask. And not pure black 9for fully transparent). In other words, a simple blur is not good for feathering images. You need to adjust your blured mask so anything that is 50% grey or darker becomes fully black.

This is probably the simplist solution.
convert blured_mask.png -negate -evaluate multiply 2 -negate feather_mask.png

WARNING: bluring like this will make a feathered masking image, but it is NOT the best way. If you get two parts of the image close together or only a very small transparent hole, the blur will not getnerate a 50% grey at those edges and the overall color of the area also effects the blur. that is for a complex shape, the result will still not be a feathered mask!

Does anyone know the algorithm to properly feather a mask? And remember this is not a simple 'blur' when the shape is also complex! this algorithm is something that should probably be implemented into ImageMagick.

Your original code is all set except the blur goes into and out of the yellow. To fix this on layer masks in Photoshop I typically push the levels of the mask one way or another. Try this after generating blur-matte.png, I think it should do what you want:

Note you will need to create a checkerboard pattern such as in my ps_checks.gif which is 8x8 pixel squares alternating white and #cdcdcd (which tries to match that of the checkerboard background from Photoshop's transparency selector).

You can also use the IM internal pattern: checkerboard, but it looks different.

Here is the command for ps_checks.gif:

convert -size 8x8 xc:white xc:"#cdcdcd" +append \
\( +clone -flop \) -append ps_checks.gif



Now, try this if on Linux or Mac:

bgcolor=`convert source.png -format "%[pixel:s.p{0,0}]" info:`
convert source.png \( -clone 0 -tile ps_checks.gif -draw "color 0,0 reset" \) \
\( -clone 0 -fill "$bgcolor" -colorize 100% \) \
\( source.png -channel r -separate +channel -threshold 0 -negate -blur 0x12 -level 40x100% \) \
-delete 0 -compose over -composite source_result.png



You can adjust it with the blur amount and the first value in -level.


This works without having to create a constant green image:

bgcolor=`convert source.png -format "%[pixel:s.p{0,0}]" info:`
convert source.png \( -clone 0 -tile ps_checks.gif -draw "color 0,0 reset" \) \
\( source.png -channel r -separate +channel -threshold 0 -negate -blur 0x12 -level 40x100% -negate \) \
-delete 0 -alpha off -compose copy_opacity -composite -compose over -background "$bgcolor" -flatten source_result.png


This works without having to get the color first, but is a bit more awkward as it has to specify the input image again:

convert source.png \( -clone 0 -tile ps_checks.gif -draw "color 0,0 reset" \) \
\( -clone 0 -tile source.png[1x1+0+0] -draw "color 0,0 reset" \) \
\( source.png -channel r -separate +channel -threshold 0 -negate -blur 0x12 -level 40x100% \) \
-delete 0 -compose over -composite ssource_result.png


Alternately (and simplest), try

convert source.png \
\( -clone 0 -tile ps_checks.gif -draw "color 0,0 reset" \) \
\( -clone 0 -channel r -separate +channel -threshold 0 -negate -blur 0x12 -level 60x100% \) \
-swap 0,1 -compose over -composite source_result2.png



But if you lower the -level 60x100% too much below 60, you will start seeing the yellow.


If on windows, then see http://www.imagemagick.org/Usage/windows