Creating an Alpha Channel

Creating an Alpha Channel

Photoshop CS3 Tutorial

 

How to Create an Alpha Channel in Photoshop

 

 

Often times images from Photoshop are used in other applications, such as After Effects, that support alpha channels. This grayscale channel has black areas to indicate transparency and white sections that are opaque.

The alpha channel can be found in Photoshop's Channels palette and is labeled as channel #4.

 

Step One

Open a new 500 pixel by 500 pixel document in Photoshop (File > New).

Step Two

Using the Text tool, add some text to the document.

Step Three

Cmd or (PC- Ctrl) click the text icon in the Layers palette to select the active pixels.

Step Four

Click the Channels palette and click the Save Selection as Channel icon.

Step Five

Notice that this creates Channel #4 (Alpha 1). Click the channel icon and notice that the text area is white and the background is black.

Step Six

By saving the image as a PSD or TIF file, the alpha channel is included with the image.

24 vs 32 Bit Images

24 bit images contain eight bits of red, eight bits of green and eight bits of blue information. A 32 bit image contains the RGB info plus another eight bit grayscale image that stores the alpha information.

Transparency and Alpha

Many programs use alpha channels to set the object's opacity. This includes video software, 3D software and compositing software. JPG images do not retain the alpha information.