What is Alpha Channel?

You can think an alpha channel as a hidden black-white picture inside a color picture. The black-white picture controls how the color picture displayed:

• If an area of the alpha channel is white, the corresponding area of the color picture is displayed normally - opaque to the background.
• If an area of the alpha channel is black, the corresponding area of the color picture is transparent to the background.
• If an area of the alpha channel is gray, the corresponding area of the color picture is partially displayed - semi-transparent to the background.

A picture with alpha channel on a white background		A picture with alpha channel on a blue background		The alpha channel

For a better understanding, lets examine a picture with an alpha channel. The first two pictures on the right are actually one same picture. It is the alpha channel that makes it look different on different backgrounds. The transparent area is white when the picture is put on a white background, and blue when on a blue background.

The web browser can not let us see what the alpha channel looks like, but with a professional application, we can save it as an separate picture. The third picture is thus aquired from the alpha channel of the first picture.

Greeting Card Templates

If we put a picture behind a picture with alpha channel, then the two pictures look as if they were one picture:

Many people make greeting card templates this way. The templates are provided in PNG format - one of the image formats that support alpha channel - JPEG does not support alpha channel. Searching "greeting card templates PNG", you can find a lot resources of this kind. Of course you need a special application to "melt" the two pictures together to get a single picture. XUEBROTHERS PhotoCutter is one of applications that can melt the two pictures together.