Step 5: Apply Filter To Just One Channel

In this step, you look at how layers can be used to modify filter effects.

In Technique 11, you'll learn how you can apply filters to remove grain in an image by only applying them to one channel — the channel that shows the most grain. For this example, we are going to do something similar. We apply a filter to a single channel.

■ If the Channels palette is not displayed, choose Window ^ Channels to get the Channels palette shown in Figure 35.10. At this point, all the channels are highlighted, meaning that any edits that you do are done to all three channels. To edit just the Red channel, click the Hide Layer icon in the left column of all layers except the red layer.

■ Choose Image ^ Adjustments ^ Posterize to get the Posterize dialog box shown in Figure 35.11. Set Levels to 4 and click OK.

■ To view all channels, click the RGB thumbnail in the Channels palette. The effect of this step is to posterize just the red colors in the trucks and to make them even more posterized.

Remember you can use the History palette to easily step back and forth between steps to view differences in effects. For example, you can click back one step to see what your image looked like before applying a filter to just the Red channel. Then click to the last step to once again see the effect of the filter. Be aware if you run another command or filter after having looked at a past history state, all future history from that state forward will go away. You do have one chance to get it

_] Jd ft back, as you can select Undo (Ctrl + Z) once to get back the old history.

The final image is probably not one you want to print out, but with these tips, you are on your way to being a master of using filters. Use these tips as starter ideas for coming up with your own ideas on how you can get the most from Photoshop filters. Before going on to the next technique, see if you can create a cool looking image or two of the two firetrucks. Then check the gallery on this book's companion Web site to see if your images are substantially different from those in the gallery at www.reallyusefulpage.com/ 50ps7/techniquesfiretrucks.htm. If they are, please e-mail a small JPEG file to [email protected] reallyusefulpage.com. I'd like to display your work in the gallery to show how different users use the same tool differently. Please make sure that the longest side of the image is 400 pixels and that it is a JPEG file.

This technique concludes this chapter. In the next chapter, we'll use some of the best plug-ins on the market to edit more digital photos.

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