1. Transparency
Skills: selecting irregular shapes with the magic wand tool, using layers
Concepts: transparency
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 License.

2. Where does this topic fit?
Internet concepts
Applications
Technology
Implications
Internet skills
Application development
Content creation (image)
User skills

3. I want to make this image …

4. by combining these two images.
How can I do that?

5. Copy green circle to red outline … fail
I tried to place the green circle on a new layer above the red circle, but it did not work.
Why not?
What went wrong?

6. What is the solution? (Hint: what is the title of this presentation?)
The actual image is a white rectangle with a green circle in the middle.
I did not notice that because the white rectangle blends into the white background.
I need to make the white background transparent so the red circle will show through the layer above it.
What is the solution? (Hint: what is the title of this presentation?)

7. Transparent background
Image editors traditionally indicate a transparent area with a grey and white checkerboard pattern.
To make the white corners transparent, I had to select them then cut away the selected area.
The magic wand is used to select irregularly shaped areas of an image.
Is there a tool for selecting irregularly shaped areas of an image?

8. The magic wand tool I used the “magic wand” tool in the image editor.
By clicking the magic wand in the upper left corner, I selected all of the white pixels.
I could then cut the selected area, leaving it transparent.
I repeated that for the other corners.
Note the tool settings.
I set the tolerance to 50%, the selection mode to replace and chose flood mode.
You must experiment with these settings when you are using the magic wand tool.
The magic wand tool

9. Which tool did I use to center the disk in the circle?
I added a new layer above the red circle, and copied the green circle to that layer. (Don’t forget to add a new layer).
Since the green circle was now on a transparent background, the red remained visible.
Since it is on a new layer, I could move it around until it was centered over the red circle.
If I had trouble centering them exactly, I could import them into PowerPoint and align them automatically.
Which tool did I use to center the disk in the circle?

10. Summary
We learned to select an irregular shape using the magic wand tool.
Then we made the background of the irregular shape transparent.
We added a new transparent layer on top of the red circle image, and pasted the green circle on it.
Finally, I moved the green circle to the center of the red circle.
Finally, I flattened the two layers creating the final image.

11. Self-study questions
In selecting the background of the green circle image, I set the flood mode to contiguous instead of global. What would have happened if I had used the global setting?
What is the difference between contiguous and global flood modes?
What happens if you click the magic wand over the green circle instead of a white corner?
How does the magic wand determine which pixels to select?
Do you select more or less area if you increase the sensitivity setting?

12. Resources Mastering Paint.net (book): http://amzn.to/XUe2B7
Short tutorial video on the magic wand tool and its sensitivity setting: