Oreilly Photoshop CS5 The Missing Manual_2

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Oreilly Photoshop CS5 The Missing Manual_2 Basic Channel StuntsNote: What’s the difference between “noise” and “grain”? They both describe tiny flecks on your image,but, technically speaking, noise occurs in digital images, whereas grain occurs in analog prints, film, andtransparencies. In other words, grain becomes noise once you scan the image.However, let’s say you’re in RGB mode and you dutifully followed the instructionson page 462 and ran the Reduce Noise filter on your blue channel (which typicallyhas the most noise, though sometimes noise can hide out in the red channel) andit didn’t do squat. What do you do? You can try bringing out some of the details inyour image by sharpening only the red and green channels, as shown in Figure 5-15. Figure 5-14: Photoshop doesn’t let you merge two channels into one, but you can combine them into a new channel with the Calculations command: Choose Image➝Calculations and, in the dialog box shown here, set the Source 1 section’s Channel pop-up menu to “Red copy” and the Source 2 section’s menu to “Green copy”. Choose Multiply from the Blending pop-up menu at the bottom of the dialog box if you want to create a black object or Screen if you want to create a white one. When everything’s set, click OK. chapter 5: controlling color with channels 215Basic Channel Stunts Tip: The next time you need to sharpen a portrait of someone who’s sensitive about his or her appear- ance, try sharpening only the red channel to avoid bringing out unwanted details in the person’s skin. (As you learned earlier in this chapter, most of the fine details live in the high-contrast green channel.) Here’s how to sharpen without making noise any worse than it already is: 1. Openyourimageandmakeacopyofthelayer(s)you’regoingtosharpen. If you’re working with a document that has just one layer, select it in your Layers panel and duplicate it by pressing �-J (Ctrl+J on a PC). If you l ...