Make an image transparent

[iam8up]

I have a script that generates and image and such and I want to overlay this on Google Maps.

The only problem I have now is that I want to make the image (PNG) something like 65% transparent. Can this be done? I'm not sure if I am doing something wrong, as every argument I've tried either gives me no result or something I do not want.

[fmw42]

try

convert image.png -alpha set -channel a -evaluate set 65% +channel newimage.png

see http://www.imagemagick.org/Usage/transf ... aluate_set

what IM version, platform and OS?

can you post a link to your image(s)?

[iam8up]

Thank you very much for the response.

This is the image I want to make transparent.
http://inxwireless.com/work/outage-orig.png

the -alpha argument doesn't take:
-> convert outage-orig.png -alpha set -channel a -evaluate set 65% +channel outage.png
convert: unrecognized option `-alpha'.

convert outage-orig.png -channel a -evaluate set 65% +channel outage.png
http://inxwireless.com/work/output.png

ImageMagick.i386 6.2.8.0-4.el5_5.3
-> cat /etc/redhat-release
CentOS release 5 (Final)
32-bit

[fmw42]

Your input image does not look like the correct link. The page is missing all images.

Your version of IM is too old (over 400 versions old) to use -alpha set and perhaps -evaluate set

If you cannot upgrade IM (highly recommended!), then

try

convert image.png -matte -channel a -evaluate set 65% +channel newimage.png

or

convert image.png -matte -channel a -evaluate set 35% +channel newimage.png

as the alpha channel at that time might be really opacity and not transparency

if that fails, try

convert image.png \( -clone 0 -fill "gray(65%)" -colorize 100% \) -compose copy_opacity -composite result.png

or

convert image.png \( -clone 0 -fill "gray(35%)" -colorize 100% \) -compose copy_opacity -composite result.png

[iam8up]

I fixed both links to images above, they should work now. Sorry about that.

I tried the first two commands and I don't see any differences between the output images and original.

The third command is missing a quote somewhere, so I did:
-> convert outage-orig.png \( -clone 0 -fill grey -colorize 100% \) -compose copy_opacity -composite result.png
Of which I don't see any change in the image either.

http://inxwireless.com/work/newimage.png
http://inxwireless.com/work/result.png

I'm guessing it has something to do with how the image is colored (alpha, palette, something of that sort). Total guess, mind you!

[fmw42]

try this (I fixed the quote and added +matte to turn off any existing alpha channel, sorry about the quote)


convert newimage.png \( -clone 0 -fill "gray(35%)" -colorize 100% \) +matte -compose copy_opacity -composite newimage_result.png

or


convert newimage.png \( -clone 0 -fill "gray(65%)" -colorize 100% \) +matte -compose copy_opacity -composite newimage_result.png


Then drop it on your browser's white background and you should see it look somewhat whiter as it is overlaid on the white background.

This also works for me:

convert newimage.png -matte -channel a -evaluate set 35% +channel newimage_result2.png

[iam8up]

I upgraded versions as your initial suggestion put. Since there is no repo for it, I had to do it semi-manually. This guide was used and was flawless short of the version (I used 6.6.9)
http://en.citizendium.org/wiki/User:Dan ... k_6.6.2-10

-> convert --version
Version: ImageMagick 6.6.9-8 2011-05-10 Q16 http://www.imagemagick.org
Copyright: Copyright (C) 1999-2011 ImageMagick Studio LLC
Features: OpenMP

This worked! Thanks so so much!
convert outage-orig.png \( -clone 0 -fill "gray(35%)" -colorize 100% \) +matte -compose copy_opacity -composite newimage_result.png

[fmw42]

With your new release, the other method should work also and is shorter and faster.

convert newimage.png -alpha set -channel a -evaluate set 35% +channel newimage_result2.png

or


convert newimage.png -alpha opaque -channel a -evaluate set 35% +channel newimage_result2.png

[Rye]

try

convert image.png -alpha set -channel a -evaluate set 65% +channel newimage.png

see http://www.imagemagick.org/Usage/transf ... aluate_set

what IM version, platform and OS?

can you post a link to your image(s)?

It works, but there is one problem.
It replaces the "already present transperency" my pictures have with "black".

Any way to keep that transparancy aswell ?

[fmw42]

So what do you want to happen? You want to reduce the opacity of all pixels from whatever they have by 65%. If so, try this

Code: Select all

convert image.png -alpha on -channel a -evaluate multiply 0.65 +channel newimage.png

[Rye]

Perfect