How to use the channel to choose the main body of the picture

The confusion of hair

Perhaps some readers have picked up the lasso or path tool, and began to outline the cat with confidence, but they almost had to pause when they sketched the cat's beard, as shown in Figure 1.67.

Figure 1.67

Whether it's a path tool, it's a way to deal with this slim hair, even if the user Dickens each beard, and when faced with those looming whiskers, it will always produce

To be born with such a puzzle: election or not?

If the beard is counted, the pixels contain more of the background, and if it counts as a background, the beard's composition remains, and the detached cat whiskers will appear unreal by ignoring these components (fig. 1.68).

Figure 1.68

The user is in a dilemma here. So, what exactly is the problem?

If users have a good habit of keeping their hard-earned selections in the channel at any time, they can look back to see what common features the selections from previous tools in the Toolbox have.

The graph shown in Figure 1.69 is a lot like an IQ puzzle. The graphics are very familiar, and are all the graphics that are stored in the previous selection to the channel. The question is: what are some common features of these graphs?

Figure 1.69

If viewed from the angle of shape or object attributes (e.g. animal or plant, life or inanimate), the reader does not see what they have in common.

Now give you a hint: look from the color angle. From the perspective of color, the problem will be very simple: only black and white. This means that if you load as a selection, these graphs provide only two choices for the image: Select or not.

Such choices are so common in life that we are faced with the choice of eating or not eating, sleeping or not sleeping, writing or not writing.

The answer to this choice is either, very easy to understand and very easy to answer, usually the children's way of thinking, the child's world is so simple, they usually refuse ambiguous choice.

This choice is in Photoshop, the tool in the toolbox that gives us choices.

However, this is a very preliminary choice. In the daily life, or just eat and sleep to learn, our choice is often: eat, but only a few mouth; sleep, but just take a nap; Write your homework, but listen.

Write on the side of music.

It seems that, in the face of choice, not just or either, we have a choice in addition to the election, there is another option: choose, but only a part of the election.

This is a transformation of the way of thinking. In Photoshop, users also have to go through this transformation. Unfortunately, not everyone can turn this corner smoothly.

Expedient--Background eraser

Before the user turns around, it's not just the choice of hair. Adobe provides a dedicated tool in the toolbox, which is the "Background eraser tool" under the eraser. It solves a part of the problem for the user.

The Background eraser tool is a more complex tool that prompts users to take some time to explore their tools options bar to find the best settings.

The first is the brush setting. For this image, it is more appropriate to set a soft side brush and to minimize the spacing. Because the photoelectric pen is not used, the related options are turned off (figure 1.70).

Figure 1.70

In the Tools Options bar, set the limit option to discontinuous, which is similar to the "contiguous" option (not checked) in the Magic Wand tool. For example, if the brush area crosses both sides of the beard, this "discontinuous" option erases the color approximation to the background color and retains the beard. Because the background is not a single color, sampling selects continuous, which allows you to select a different sampling point each time you click the left mouse button. Because the beard and background color difference is more obvious, "tolerance" can be set slightly larger, for 50%.

After you set the brush, to get a clearer picture of the changes before and after the background erase, you can fill a black layer under layer 0 as a substrate (figure 1.71).

Figure 1.71

To move the brush to a document, unlike other drawing tools, the brush has a cross cursor at the center, which is the point of sampling. As the cursor moves, the color of the brush range of pixels is constantly compared to the color of the sampling point, depending on the tolerance, the more the difference between the sample point and the larger the color retention, the difference between the small color is different degree of erasure (Figure 1.72).

Using continuous sampling to erase the background there is a trick: never hold down the left mouse button to move and across the beard, the process of an instant beard will be as a sampling point to cause the beard was removed. The right thing to do is to use a mouse click and notice that the beard is skipped.

Figure 1.72

After you hide layer 1, you can see the transparent area exposed after the erase background (figure 1.73).

Figure 1.73

The Background eraser tool is a useful tool for erasing the background (colloquially called "Pull Up"). It sometimes offers another huge go-to background tool than Adobe does-"Pull out" filter

The mirror is much simpler and easier to use.

However, the "Background eraser tool" is only a dedicated tool, the image Processing task is not just to pull the map. Most of the time, we don't need to separate the cat from the background, but we need to change the background without touching the beard.

To do this, you need to have a deeper understanding of Photoshop.

Black and white in the middle of a bridge-color range command

In Photoshop, there is a very powerful choice of command, can lead users across the choice of black and white huge gap, into the choice of a new world. This command is located under the "Color range" command under the "Select" menu.

In a rough look, there are many similarities between this command and the Magic Wand tool, for example, they all have a "tolerance" option, which is also determined by the sampling point color value as the benchmark. However, unlike the magic wand tool, this command first introduced a very important concept in Photoshop--gray--into the selection. Between black and white, there is a series of gray with a homogeneous transition, which indicates the number of choices (figure 1.74).

Figure 1.74

The Color Range dialog box provides a preview window that is usually not enough to make the user see the details of the selection, so it is a good idea to set the selection preview to grayscale so that the user can see if the appropriate area is selected in the range of the image size. In this illustration, the pixel value of the eyedropper clicks separates the beard from the background with the adjustment of the Color Tolerance slider.

Once identified, the selection defined in the dialog box appears on the screen as an ant line. We seem to have seen the ant line after using the Magic wand tool. However, it should be noted that at this point the ant line indicates only the boundary line of more than 50% choices (that is, the area below 50% grayscale seen in the dialog box) (Figure 1.75).

Figure 1.75

At this time the ant line has no indication of any significance.

In a sense, if the user persists in the mind of the ant line, it begins to become the Chinmaso of the binding choice of thinking.

Is that a choice? How is it so similar to the original image? Many readers are accustomed to the silhouette choice, which is naturally not adapted to the grey choice of the mixture. However, this is indeed an option. When loaded as a selection, black is the protected area, and white is the area where pixels can be manipulated. What about the gray? is the area that can be partially manipulated, conversely, is a partially protected area (figure 1.76).

Figure 1.76

Because the background is a protected area, use the "reverse" command to reverse the image, now the background is white. What about the beard that made us so embarrassed? Please do not say to become black, it presents a series of uniform changes from black to gray. This indicates a different degree of protection.

Figure 1.77

Save the selection as a "ALPHA1" channel (Figure 1.77).

It is usually necessary to do some processing on the "ALPHA1" channel image, which can save us a lot of trouble in the background erasure operation later.

Select the Eraser tool to erase the background of the cat with some gray or white areas. Viewed from the image, we erase the operation is more casual.

That is true, but it is not irresponsible. In theory, the cat's entire body should be protected black, but the middle is not painted black. The eraser will not arrive here because of subsequent erase background operations (figure 1.78).

Figure 1.78

The next action should be to load the "ALPHA1" channel as a selection and erase the background.

But wait a minute, in order to better see the effect of erasing, we need a substrate. This time, we no longer fill a black layer as a substrate, but instead drag a picture of a landscape, possibly a street park (Figure 1.79).

Figure 1.79

Load the "ALPHA1" channel and make the cat's "layer 0" the current layer. The familiar ant line appears again, but now it does not help us a little, it will only hinder the operator's view, press the "CTRL+H" key combination to hide it (figure 1.80).

Figure 1.80

You can use the Eraser tool in the toolbox to safely erase, but the erasure process also requires some skill.

First, the cat's body first to wipe out a profile, the beard especially need to be cautious, it is best not to release the mouse to ensure that the wipe evenly. Second, after the basic finish erase, you can hide "Layer 1" to see which areas remain without erasing pixels. Third, erase residue traces (figure 1.81).

First, the cat's body first to wipe out a profile, the beard especially need to be cautious, it is best not to release the mouse to ensure that the wipe evenly. Second, after the basic finish erase, you can hide "Layer 1" to see which areas remain without erasing pixels. Third, erase residue traces (figure 1.81).

Figure 1.81

You can use the lens blur filter in the Filter menu Blur filter group to blur the background to highlight the cat (the original background is a blurry background) (Figure 1.82).

Figure 1.82

Figure 1.83

Now the cat has run into the street park from whose house. Its beard is still so eye-catching, but naturally into the new background, which is entrusted with the "color range" command of the blessing. Through this bridge between black and white, the cat came to a new world, the reader also from the simple black-and-white world came to a broader gray-scale (Fig 1.83).

Category:

• PS Pull Map Tutorial