Alpha Channel Discovery

A Second Life Tutorial by Robin (Sojourner) Wood. All rights reserved.
(Copying these pages and selling them as-in in Second Life, in any format whatsoever, is specifically prohibited.)

This is the second page of a 3 page tutorial. To see the first page, click here.

Click on the word "Green" in the Green Channel, and the image in the right hand window becomes pure black again. This is because all the pixels in this channel are still set to zero, from when we flooded the image with Black (Red:0, Green:0, Blue:0.)

Click the word Green to Select the Green Channel

Draw another squiggle, any squiggle, in a different direction, so that it will cross the first squiggle at some point.

When you finish drawing, you'll see that this one is bright Green (Red:0, Green:255, Blue:0,) because you were using white, and therefore putting the maximum value into the Green channel.

A white squiggle in the Green channel makes a mark that's R:0, G:255, B:0. But where is crosses the red line, you get R:255, G:255, B:0, which is yellow!

But, where the lines in the Green and Red channel cross, you'll see Yellow! That's because those pixels have 255 in both the Red and Green channels. Yellow is Red:255, Green:255, Blue:0. So that's what you get. (Run the mouse over the image, to see the numbers.)

You can probably guess what will happen when we draw a line in the Blue channel. But go ahead and try it anyway.

A white Squiggle in the Blue channel makes a Blue line (R:0, G:0, B:255), which is Cyan (R:0, B:255, G:255) where it crosses the Green, Magenta (R:255, G:0, B:255) where it crosses the Red, and White (R:255, G:255, B:255) where it crosses the Yellow

As you might expect, where it doesn't cross either of the others, you get Blue. Where it crosses the Green line, you get Cyan (R:0, G:255, B:255). Where it crosses the Red line, you get Magenta (R:255, G:0, B:255.)

And where it crosses the Yellow, you get White (R:255, G:255, B:255.)

Click the Color Swatch, and get a nice, 50% Gray. (If you're using the Adobe picker, click the B, for Brightness, and enter 50%. This lets you pick the Intensity of the - something - on the channel more directly. Hue can be anything, as long as the Saturation is 0%.)

Use the Color Picker to get 50% gray

Scribble some more. Notice that, this time, you're getting darker shades of the pure colors. That's because you're only using half the intensity.

This time, instead of putting R:255 in the red channel, you're putting R:128. So each pixel that you have changed will have R:128, along with whatever values are in the Green and Blue channels. Run the mouse over the image, to see the numbers.

Using Gray (value=128) will give you colors that have a R:128 with whatever they have in the other channels.

Click on the Window on the Left to enable it, and click on the RGB at the top of the Channels Palette so you'll be working in full color. (If you skip this step, you'll still be working in a single channel, and the next directions won't work. So don't skip it.)

Click the composite RGB to select all three color channels at once, so you can work in Full Color

Use the Eyedropper to pick up the color in one of the pure dark red areas, that doesn't cross any other colors.

Use the Eyedropper to pick up some of the Dark Red, so you can examine the numbers for yourself.

Click on the Color Swatch, and it will open the Color Picker, so you can see what the RGB values are. You'll find that you have R:128, G:0, B;0.

If you look at the RGB values, you can see your levels of gray, reflected perfectly

Use the eyedropper to check some other colors. Try experimenting with other shades of gray, and see what that gets you.

Play and experiment, until you are comfortable with the way that channels work, and how they are simply grayscale images of how much - something - you have.

If you'd like some ideas about directions you can go with your experiments, click here.

Otherwise, go in whatever direction you like, have a ball with it, and keep playing until you feel very comfortable with what Channels do, and you can predict what will happen when you do stuff to the channel.

When you're ready, click here to go on to the next section of this tutorial.

 

If you would like to see the other tutorials in this series, click here.

Everything on this site is copyright © Robin Wood; all rights reserved. Feel free to link to these pages, print them out for yourself, and use them yourself to create content for Second Life without restrictions. However, you may not distribute them in any way, (post them on your site, put them on a CD, use printed copies as handouts in a class, make books out of them to sell in SL, etc.) without permission. To get permission, write to Robin, and explain what you intend to use it for.