Photoshop users, How do you create an alpha channel?

Question

What's the easiest way to create an alpha channel in Photoshop? How do you turn your image into solid black and white?

I use alpha channels to import images into InDesign, is there any other reason Alpha Channels is used for?

Thanks for your help.

Answer 1

Any mask is an alpha channel, another way to create one is to make a selection and save it, it is automatically saved as an alpha channel. They can be changed into a spot channel by selecting it and using the channel options changed to a spot channel. You can copy and paste a colour (rgb or cmyk) channel into an alpha channel.

To turn your image to a solid black and white, the simplest way is to convert to greyscale mode and then to bitmap mode, the options you choose during this sequence will produce radically different effects. An alternative is to create a greyscale and work with levels to create black from the grey tones, brightness and contrast will perform a similar function.

Answer 2

The Alpha channels are basically templates for a selection that you have set up in an image.

In image editing on the computer, a portion of each pixel's data is reserved for transparency information. 32-bit graphics systems contain four channels -- three 8-bit channels for red, green, and blue (RGB) and one 8-bit alpha channel.

The alpha channel is really just a mask, it specifies how one pixel's colours should be merged with another pixel's when the two are overlaid, one on top of the other. The main difference between a normal selection and an alpha channel selection is the ability to save and copy, the selection, across to other images.

Some explanations and tutorials can be found here...

http://www.photoshopcafe.com/

There is a good line art tutorial here...

http://www.melissaclifton.com/tutorial-c...

To turn the image into solid black and white, either use the desaturation tools, ctrl+alt+U, or use the thresh hold filters.

If you simply turn the image into a grey scale image you will not be able to add colour to it, if you desaturate it you can still add colour to it for some interesting effects.

Good luck and have fun.