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Tài liệu Photoshop cs5 by Dayley part 59

Tạo tùy chỉnh ảnh đen trắng Khi bạn chuyển đổi một hình ảnh màu thành ảnh đen và trắng, bạn có thực sự kết hợp ba kênh (đỏ, xanh lá cây, và màu xanh) của dữ liệu vào kênh màu xám chỉ có một. Điều này có thể được thực hiện trong nhiều cách. Tuy nhiên, có ba khái niệm chính. Một cách để chuyển đổi một hình ảnh màu sang màu xám là chỉ sử dụng một trong ba kênh, ví dụ, chỉ có các kênh màu đỏ | Chapter 13 Lighting and Color Adjustments On the Web Site The image shown in Figure 13.16 can be found on this book s Web site as Figure13-16.jpg. Check out the file on the Web site and make the changes shown in the example to see the detail come back and the brightness get toned down. Creating customized black and white photos When you convert a color image into a black and white photo you are really combining three channels red green and blue of data into only one grayscale channel. This can be done in any number of ways. However there are three main concepts. One way to convert a color image to grayscale is to use only one of the three channels for example only the red channel. The problem is that this gives you only the red data in the image leaving much of the detail out. This works well for some effects but you likely want more detail in your image. Another way is to use a combination of the three channels. For example you could create grayscale data by taking 40 percent of the red value 40 percent of the green value and 20 percent of the blue value and adding them together to get the value for each grayscale pixel. By using the best combination of the three channels you can get the most detail out of the image. This works very well as you learned in the Channel Mixer section of Chapter 11. In fact this is the default method that Photoshop uses to convert color images to grayscale and is the recommended method of conversion. A little bit more complex way to generate the grayscale data from the color channels is to focus on percentages of each color tone. This allows you to maximize the amount of detail best contrast and overall appearance of the resulting black and white photo. The drawback to this method is that it requires some guesswork and a bit of trial and error to get the best effect. The Black and White Adjustment tool shown in Figure 13.17 allows you to use combinations of reds greens and blues as wells as cyans magentas and yellows to generate the .