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)
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.
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.
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.
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.
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 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 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.
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 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.
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.
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.