Selections & Masks in Photoshop-- Part III

Article and Photography by Ron Bigelow

www.ronbigelow.com

Photoshop CS or Photoshop CS2 Used in this Tutorial

The tools introduced in the previous two articles are fairly well known as selections tools. In this article, the tools that are introduced are also well known, but not necessarily as selection tools. However, their ability to separate tones makes them ideal for selections.

Selection: Curves

Curves is an excellent tool for creating selections. As all of the tools in this article, Curves works best on selections that are based on tone. It is assumed that the reader knows the basics of Curves (for more information on Curves, see Curves -- Part I)

Figure 1: Image that Needs Adjustments to the Flowers
Figure 1 shows an image with white flowers. It is desired to edit the flowers without affecting the rest of the image. Figure 2 shows the Layers palette before any work begins.
Figure 2: Layers Palette before Work Begins
Figure 3: Layers Palette after Grayscale Layer Added
The first step is to duplicate the image (drag the Background layer down to the Create a new layer button at the bottom of the Layers palette). The new layer is renamed the Grayscale layer. Figure 3 shows the Layers palette after this step.
Figure 4: Image after Desaturate
Next, the Grayscale layer is turned into a black and white layer (choose Image/Adjustments/Desaturate). The image appears as shown in Figure 4.
Figure 5: Image after Eyedroppers Applied
Curves is now used to increase the contrast between the areas that are to be selected and those that are not. With the Grayscale layer selected, Curves is launched (Choose Image/Adjustments/Curves), the eyedroppers are used for the first step in increasing the contrast. The White Eyedropper is clicked on the white flowers. Then, the Black Eyedropper is clicked on one of the areas that is not to be selected (this area must be darker that the flowers). The result is an increase in contrast as seen in Figure 5.
Figure 6: Curves
This is a good start. On the other hand, there are some gray areas. As is, if a selection were made at this time, these gray areas would be partially selected. This is not acceptable as these areas shouldn't be selected at all. A further increase in contrast is needed. Luckily, applying a curve to the image will achieve this goal. With Curves still open, a curve is applied to the image (see Figure 6). Figure 7 shows the image after the curve was applied.
Figure 7: Image after Curves Applied
This is pretty good. Nevertheless, it is not good enough. The areas just above the top flowers have some gray tones. These gray tones need to be eliminated. It is time for another selection technique.

Selection: Blend Modes

Figure 8: Image after Vivid Light Blend Mode Applied

A further increase in contrast will force the gray areas that still exist in Figure 7 to either black or white. This is easily done through the use of Blend Modes. For this step, the Grayscale layer is duplicated (drag the Grayscale layer down to the Create a new layer button at the bottom of the Layers palette). The Blend Mode of the new Grayscale copy layer is set to one of the contrasty Blend Modes (select the Blend Mode on the Layers palette). The Vivid Light Blend Mode is used for this image. The image as it appears at this time is shown in Figure 8. This image clearly shows that most of the gray tones have been forced out of the image. Figure 9 shows the Layers palette after this step.

Figure 9: Layers Palette after Vivid Light Blend Mode

For this image, the Blend Mode technique was used only once. With other images, even more contrast might be required. In that case, this procedure can be repeated. The Grayscale layer can be duplicated again and the Blend mode of the new layer set to one of the contrasty Blend Modes. In fact, this process can be repeated several times if necessary.

While the image in Figure 8 is better than ever, there are some white areas next to the flowers that need to be eliminated. Thus, this image still needs some clean-up. However, the clean-up will have to wait until after the image is turned into a selection.

Figure 10: Channels Palette

To turn the image into a selection, the Channels palette is selected (see Figure 10). If not already selected, the RGB channel is selected. To create the selection, the Load Channel as Selection icon at the bottom of the palette is clicked.

Figure 11: Selection

Moving back to the Layers palette, the Grayscale layers are deleted as they are no longer needed. The selection is shown in Figure 11.

This selection is pretty good, but it is not perfect. It needs some clean-up work. This clean-up is done using the techniques already presented. Lastly, the selection is turned into a mask as was done in the previous article.

Figure 12: Final Mask
Figure 12 shows the final mask and Figure 13 shows the final Layers Pallet after the mask was applied to a Curves layer.
Figure 13: Final Layers Palette

Selection: Channels

Using Curves the way it was applied in the example above is a good method of making selections. Nonetheless, there is a better way. In the previous example, Curves had to deal with the tonality of the entire image. The problem is that the tonality of the areas that need to be selected might not be that much different than the areas that should not be selected. This makes it much more difficult to make a successful selection. It would be much better if, before Curves was applied, the contrast between the areas to be selected and those that are not to be selected was greater. This can actually be achieved in many images by using the Channels.

Figure 14: Image Ready for a Selection

Figure 14 shows an image where it is desired to select the violet colored portions of the flowers. Then, work can be performed on just these areas.

Figure 15: Grayscale Copy of the Image

Figure 15 shows what the image would look like if it were converted to grayscale as in the method used above. The problem is that there are gray areas within the flower petals. There are also gray areas in the background. If Curves is used on this grayscale layer, it will not produce a clean selection, and quite a bit of clean-up work will be required.

However, moving to the Channels palette and viewing the three channels (see Figures 16 -- 18) reveals an interesting discovery. The red and green channels don't help much with this selection. There is poor contrast between the areas that need to be selected and those that don't. On the other hand, the blue channel has a large amount of contrast. The areas that need to be selected are very light, and the rest of the areas are very dark. This is a great starting point. The blue channel will be used as the starting point for the selection.

Figure 16: Red Channel
Figure 17: Green Channel
Figure 18: Blue Channel
Figure 19: Channels Palette after New Channel Created
To begin the selection process, the blue channel is duplicated (drag the channel to the Create a new Channel icon at the bottom of the Channels palette). The new channel is renamed the Selection channel. Figure 19 shows the Channels palette after this step. Curves is now applied to the Selection channel in exactly the same manner as in the previous example.
Figure 20: Curves
Figure 20 shows the Curve used on this image. Figure 21 shows the Selections channel after Curves was applied.
Figure 21: Selections Channel after Curves
Figure 22: Selection
The Selections channel looks pretty good. To turn the channel into a selection, the channel is chosen, and the Load Channel as Selection icon at the bottom of the palette is clicked. Figure 22 shows the selection.
Figure 23: Final Mask
A bit of clean-up along with a slight blurring and the selection is turned into the mask shown in Figure 23. The Final Layers palette is shown in Figure 24.
Figure 24: Final Layers Palette
One last note on this method. This procedure could have been performed with Levels instead of Curves. However, some flexibility as far as adjusting the contrast would have been lost.

Selection: Channel Mixer

Another option for creating selections is the Channel Mixer. The Channel Mixer allows the three color channels to be combined in such a way as to maximize the contrast between the areas to be selected and all of the other areas.

Figure 25: Image Ready for a Selection

Figure 25 shows an image with a lot of green. It is desired to select the green areas for editing. However, in this image, there are many shades of green. In addition, there is green in the trees along the river, green in the river, and green vegetation growing on the steep mountain behind the river. This would be a bit of a challenge with some of the other tools. On the other hand, the Channel Mixer will handle this fairly well.

In order to decide how to adjust the settings of the Channel Mixer, the channels must first be studied in order to understand the contrast in each of the channels. For this, the Channels palette is selected. Figures 26 -- 28 show the three channels.

An examination of the channels quickly shows that the Red and Green channels do not provide much contrast between the green areas and the others areas. However, the blue channel does. In this channel, the green areas are very dark and contrast against the surrounding scenery. Thus, the blue channel will be used heavily in the Channel Mixer.

Figure 26: Red Channel
Figure 27: Green Channel
Figure 28: Blue Channel
Figure 29: Layers Palette after the Mixer Layer was Added
To proceed with the selection, the Layers palette is selected and the Background layer is duplicated (drag the Background layer down to the Create a new layer button at the bottom of the Layers palette). The new layer is renamed the Mixer layer. Figure 29 shows the Layers palette after the new layer has been added. With the Mixer layer selected, the Channel Mixer is launched (choose Image/Adjustments/Channel Mixer).
Figure 30: Channel Mixer
In the Channel Mixer dialogue box, the monochrome option is checked. The Red, Green, and Blue sliders are adjusted to maximize the amount of contrast. Moving one of the channel sliders to the right increases the amount of information taken from that channel. Conversely, moving one of the sliders to the left decreases the amount of information taken from that channel. The Constant slider is used to adjust the overall brightness of the image. For this image, the blue slider is moved to the far right to get the maximum amount of information (i.e., contrast) out of the blue channel. Some experimentation yielded a best result when some information was also taken from the green channel, and the information from the red channel was reduced. Figure 31 shows the Mixer layer after the Channel Mixer was used.
Figure 31: Image after Channel Mixer
While not perfect, this is a good start. The contrast needs to be further increased. This is easily done by using the Blend Mode technique previously covered (the Hard Light Blend Mode works best on this image). Once the Blend Mode technique has been used, the image appears as shown in Figure 32 and the Layers palette appears as shown in Figure 33.
Figure 32: Image after Blend Mode Technique
Figure 33: Layers Palette after Blend Mode Technique

To turn the image into a selection, the Channels palette is selected. If not already selected, the RGB channel is selected. To create the selection, the Load Channel as Selection icon at the bottom of the palette is clicked.

Figure 34: Selection

Moving back to the Layers palette, the Mixer layers are deleted as they are no longer needed. The selection is shown in Figure 34.

This selection is good, but some clean-up work is needed. Then, the selection is inverted and turned into a mask as was done in the previous article.

Figure 35 shows the final mask after the clean-up work was done and Figure 36 shows the final Layers Pallet after the mask was applied to a Saturation layer.

Figure 35: Final Mask
Figure 36: Final Layers Palette

Articles

Selections -- Part II     Selections -- Part IV