Make the background of an image transparent

Hello,

The first thing to know when talking about transparency is that not all image formats handle it the same way.

As an example, here are 3 common formats:

• The JPG/JPEG format does NOT support transparency,
• The GIF format only handles two levels of transparency (in addition to being limited to 256 colors),
• The PNG format supports 256 levels of transparency.

So, if you are using a JPG image, for example, you will need to save it as a PNG after making parts of the image transparent, otherwise that transparency will not be preserved.
;)

The second thing is that you need to add an alpha channel: it's what will contain the transparency information (which parts will be transparent, with what level of transparency...).
;)

On the software side:

• Photofiltre 7 (free): http://www.commentcamarche.net/download/telecharger-34090233-photofiltre-7
  • /!\ Warning, as specified:
  • The installation version includes the Ask Toolbar. Uncheck the option during installation if you do not want to install it.
• Gimp (free and open-source): https://www.commentcamarche.net/telecharger/photo-graphisme/11145-the-gimp/

An example, with this image:
https://pix.toile-libre.org/upload/original/1360212716.jpg

Since the image is in JPG format, the first thing: add an alpha channel.

• In Photofiltre 7: Image > Mode > RVBA (alpha channel)
• In Gimp: Layer > Transparency > Add Alpha Channel.

Then... well, select the parts of the image you want to make transparent, and delete...

The selection tools in Photofiltre 7:
https://www.cjoint.com/13fe/CBhgh5BBIh0_capture01.jpg
If you want to remove a whole color, like here, the black, Image > Transparency Color. In the window that appears, choose black:
https://pix.toile-libre.org/upload/original/1360213907.jpg

Once the areas are transparent: File > Save As, and choose PNG.
;)

With Gimp, the principle is the same, add an alpha channel, use the selection tools:
https://pix.toile-libre.org/upload/original/1360214250.jpg
...and delete the parts of the image...

You can also choose to remove a color globally like in Photofiltre: Layer > Transparency > Color to Alpha.
Then, File > Export, and there too choose PNG.
;)

Note that in both software, to indicate which parts are transparent, they appear as a checkerboard pattern:
https://pix.toile-libre.org/upload/original/1360214795.jpg
... this checkerboard is only there to show you the transparent areas and will not be visible once the image is saved...
;)

More info on transparency and the alpha channel:
http://leblogdugnou.blogspot.fr/2012/03/transparence-et-canal-alpha-images.html
http://leblogdugnou.blogspot.fr/2012/12/retour-sur-le-canal-alpha.html
;)

@+

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