1

I have followed the instructions in this question in order to cut our the paper-white background from an image and turn it into a transparent alpha surface.

The original image (alpha_orig.jpg)

enter image description here

Magic-wand selections

enter image description here

The outcome in GIMP

enter image description here

The .png exported image

I have exported the file in .png format. The file seems to have an alpha channel:

ExifTool Version Number         : 9.65
File Name                       : alpha.png
Directory                       : /tmp
File Size                       : 773 kB
File Modification Date/Time     : 2016:02:17 12:32:07+02:00
File Access Date/Time           : 2016:02:17 12:35:28+02:00
File Inode Change Date/Time     : 2016:02:17 12:32:11+02:00
File Permissions                : rw-r--r--
File Type                       : PNG
MIME Type                       : image/png
Image Width                     : 1357
Image Height                    : 988
Bit Depth                       : 8
Color Type                      : RGB with Alpha
Compression                     : Deflate/Inflate
Filter                          : Adaptive
Interlace                       : Noninterlaced
Background Color                : 255 255 255
Pixels Per Unit X               : 2835
Pixels Per Unit Y               : 2835
Pixel Units                     : Meters
Modify Date                     : 2016:02:17 10:32:03
Image Size                      : 1357x988

However, the exported image still the has the paper-white background (tried opening it in the Chrome browser).

enter image description here

The funny thing is, when the result alpha.png file is opened in gimp - it sees the alpha channel and the image has transparency!

enter image description here

I'm using GIMP 2.8.14 on OSX.

Any idea how to export a PNG with an alpha channel so that all common image viewers will recognize it?

Update

Thanks for the answer - it now works both in PNG and JPEG.

enter image description here enter image description here

2

When choosing the Color to Alpha transformation in Gimp you will only have one single color as 100% transparent.

All other colors in that image will still be present having more or less transparency depending on the amount of the transparent color they had in the first place. In case you had chosen white as the color for alpha your transparent image will look just the same on a white background.

To obtain a fully transparent background:

  • add an alpha channel (Layer > Transparency > Add Alpha Channel)
  • Select the background or just invert your foreground selection (CtrlI)
  • remove the content of the selection (Del)
  • 2
    Or use a layer mask instead of [DEL] so you can edit it later – PieBie Feb 17 '16 at 13:41
  • The whole point of Color to Alpha is to get an image that is indistinguishable from the original if you compose it on top of the color you chose to made transparent. – Michael Schumacher Feb 18 '16 at 7:22

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