Layers is one of the most powerful capabilities of Photoshop. This capability allows photographers to apply edits to specific layers rather than to the original image data. However, the full potential of Layers is not realized until it is combined with the use of masks. Masks allow a photographer to restrict the effects of layers to specific areas of an image; for instance, one may darken the sky without darkening the rest of the image. In most cases, in order to create a mask, a selection must first be created. Selections divide images into three areas: the areas where the pixels are completely selected, the areas where the pixels are partially selected, and the areas where the pixels are not selected. Once a selection has been turned into a mask, the mask will determine how the associated layer influences the image based on the selection of the pixels.
This all appears very straightforward. Yet, as many photographers will testify, it is much harder to carry out in practice that it sounds. This is due to two issues. First, it is not always easy to select the correct pixels. Often, a method of selection will ignore some of the pixels that need to be selected; at the same time, it may select pixels that should not be selected. Second, it is often difficult to create a selection so that the resulting mask blends the selected and non-selected pixels in such a manner that the use of the mask is invisible.
Yet, photographers accomplished in the use of selections routinely create complicated selections that gracefully blend layers in a seamless manner. So, what do these photographers know that some others do not? Well, for starters, they know how to choose the correct tool for the job. These photographers know a multitude of selection tools and techniques, and they know which tools and techniques work best in which situations. On the other hand, photographers less adept in selections often know only a few selection tools and techniques. As with a mechanic who only has a pair of pliers when he really needs a torque wrench, the results can be less than desired.
With this in mind, this series of articles reviews several selection and masking tools and techniques. The series starts with the simplest approaches and gradually progresses to more sophisticated ones.
The Marquee tools are probably the simplest of all the selection tools. The Marquee tools can be found on the Tools palette (see Figure 1). There are four Marquee tools:
Figure 2 shows the Marquee Options bar. On the left side of the bar are four selection options:
The question quickly comes up, "Which is best: feathering, anti-aliasing, both, or neither one?" In general, the answer is: neither one. Different selections require different amounts of softening of the edges in order to get a good transition from the selected to non-selected areas. For example, an image from a thirteen megapixel camera will usually require more softening (i.e., a wider transition region) than an image from a six megapixel camera (all else being equal) because any given amount of detail is spread across a larger number of pixels in the image taken with the thirteen megapixel camera. Another case in point, an image of a baby's face would usually require a softer edged selection than an image of cactus needles. The problem is, at the time of the selection, it is generally not known exactly how much softening of the selection will work best. Some experimentation will likely be required. However, when a selection is made with feathering or anti-aliasing, the softening is built into the selection. While the edges can be made softer, it is more difficult to make the edges harder. Thus, if a photographer uses feathering or anti-aliasing and later decides that the selection has an edge that is too soft, he will probably have to redo the selection -- probably a time consuming task. Luckily, there is a better option. If the feathering and anti-aliasing options are not used, a Gaussian Blur can be used on the completed selection to soften the edges (this approach will be covered later in this article). If the photographer later decides that the edges need a different amount of softening, the photographer can go back to the original selection (saved before any Gaussian Blur was used) and try a different amount of Gaussian Blur. Thus, it is recommended that Gaussian Blur be used to soften the edges of the selection rather than the feathering or anti-aliasing options.
The style option (enabled with the Rectangular and Elliptical Marquee tools) allows for three options (see Figure 3):
If the Fixed Aspect Ratio or Fixed Size options are chosen, the width and height options must be entered. If the Fixed Aspect Ratio option is chosen, the width and height are entered as a ratio (e.g., 1.5:1). If the Fixed Size option is entered, the width and height are entered in pixels.
Figure 5 shows the image after the Elliptical Marquee tool was dragged across the image to create the selection. At this point, the selection has a hard edge. This selection needs to be softened, so the image is move into the Quick Mask Mode (click on the Edit in Quick Mask Mode on the Tools palette).
Figure 6 shows the selection in the Quick Mask Mode. The area that has not been selected is shown in red. To soften the edge, Gaussian Blur is launched (choose Filter/Blur/Gaussian Blur). Figure 7 shows the Gaussian Blur dialogue box.
Figure 9 shows the Layers palette. Figure 10 shows the final mask.
The Lasso tools provide somewhat more flexibility than the Marquee tools. The Lasso tools can be found on the Tools palette (see Figure 11). There are three Lasso tools:
The Lasso tool is the first of this group of tools. This tool allows a photographer to create a freehand selection.
Figure 12 shows the Options bar for the Lasso tool. The Lasso Options bar has the same Selection, Feather, and Anti-alias options as covered in the Marquee tools section.
The Lasso tool is great when an irregular shaped selection that does not require straight edges needs to be created. Figures 13 and 14 show an example where the Lasso Tool is ideal. These two images are of the same scene except the first image was exposed to keep detail in the shadows, and the second image was exposed to keep detail in the sky. The two images are put into the same file and a mask is used to blend them.
The selection is simply drawn freehand on the image (see Figure 15).
The second Lasso tool is the Polygonal Lasso. This tool allows a photographer to create a hand drawn selection that has straight edges.
Figure 18 shows the Options bar for the Polygonal Lasso tool. The Polygonal Lasso Options bar has the same Selection, Feather, and Anti-alias options as covered in the Marquee tools section.
The last Lasso tool is the Magnetic Lasso. This is a great tool when a selection is needed that borders high contrast edges.
Figure 23 shows the Options bar for the Magnetic Lasso tool. The Magnetic Lasso Options bar has the same Selection, Feather, and Anti-alias options as covered in the Marquee tools section. However, there are additional options that do not exist with the other Lasso tools. The width option determines the width (in pixels) over which the Magnetic Lasso tool will detect an edge. The larger the width, the farther from the curser the Magnetic Lasso tool will be able to detect an edge. The Edge Contrast determines how much contrast is needed before the Magnetic Lasso tool can detect an edge. The larger the Edge Contrast setting (in percent), the greater the contrast that will be needed for the Magnetic Lasso tool to detect an edge. The Frequency determines how often the Magnetic Lasso tool anchors the selection to the edge. When enabled, the Stylus Pressure icon varies the width over which the Magnetic Lasso will detect an edge.
The selection is drawn by clicking the Magnetic Lasso Tool at the starting point and dragging it across the edge (see Figure 25). The Magnetic Lasso tool will add anchor points allow the edge. Clicking along the edge will manually add an anchor point. Hitting the Delete key will delete the last anchor point.
One of the most popular selection tools is the Magic Wand. The Magic Wand tool works best on images where the selection is based on color. The Magic Wand can be found on the Tools palette (see Figure 28).
Figure 29 shows the Options bar for the Magic Wand tool. The Magic Wand Options bar has the same Selection and Anti-alias options as covered in the Marquee tools section. However, there are additional options that are unique to the Magic Wand tool. The Tolerance option determines the range of colors that will be selected. A low Tolerance setting will cause the Magic Wand to select only colors that are very similar to the color that was clicked. A high Tolerance setting will cause the Magic Wand to select more colors. When the contiguous option is checked, the Magic Wand selects only areas that are bordering the pixels that are clicked. Otherwise, all colors within the selected color range will be selected no matter where they are located in the image. When the Sample All Layers option is checked, the Magic Wand will base the selection on all of the layers. Otherwise, the selection will be based on the colors in the active layer only.