We use the Elliptical Marquee Tool, turn off and on anti-aliasing (also known as anti-aliasing), create two approximately the same size circular selections, and then fill them with black. Do you remember how to quickly fill in black? First [X] and then [ALT DELETE]. After filling, deselect [CTRL D], the effect is as shown on the left.
If you look closely at the edges of the two circles, you will see that the edge of the first circle is relatively sharp and has obvious steps, also called jagged edges. The second circle is relatively smooth. In the previous lesson #02, we have learned that the reason for aliasing is caused by the characteristics of bitmap images. Because bitmap images use small square dots to describe images, aliasing will occur when describing curves and straight lines at some angles.
So why doesn't the second circle have teeth? Really not? Let’s enlarge the image using [space CTRL click] or [CTRL +] to take a look. As shown below on the right.
You can see that the second circle actually has jagged edges, but the edges of the jagged edges have become softer. There is a transition effect from black to background white. So it looks smoother than the first circle. This is the effect of anti-aliasing. The so-called anti-aliasing does not really eliminate it, but just uses a "eye-catching method" to make the image look smoother. As long as the image is lattice, aliasing will always be there.
Vector images are structurally non-aliased, but due to the physical characteristics of the monitor being a dot matrix display, the vector image will also have aliasing when it is finally displayed on the screen. In other words, the real advantage of vector images is not reflected in the final performance, but in the image production process, which can be stretched and deformed without losing quality.
If you are careful, you will find that the rectangular, single-row and single-column marquee tools do not have anti-aliasing options. Why? Think for yourself. The answer is at the end of this section.
0414 Speaking of feathers, do you think of a soft feeling? The feathering option also does this. Now use the Elliptical Marquee Tool, set the feathering to 0 and 5, create two perfect circular selections in sequence, and then fill them with black (〖D〗,〖ALT DELETE〗). Do not cancel the selection. The effect is as shown on the left. You can see that after using a 5-pixel feather, the fill color is no longer limited to the dotted box of the selection, but extends outside the selection and gradually fades.
After zooming in, you can see that the fade effect is centered on the dotted line of the selection and extends both inside and outside the selection. As shown in the middle picture below. At this time, if you use a 10-pixel brush tool and select a red color to draw in the selection, the effect as shown on the right will appear.
We said before that once a selection is established, almost all operations are only effective within the selection, but why can the brush now have effects outside the dotted box of the selection? Moreover, the previously filled black is not completely within the selection, and part of it exceeds the dotted line of the selection. This is because the dotted box of the selection sometimes does not completely represent the selected range. This problem will be explained later in this article.
The function of the Feather option is to blur the edges of the selection, so that you can get a softer transition when creating composite effects. Now open the following 2 images in Photoshop.
