Gaussian blur mặc định mà không có cạnh bảo vệ cho kết quả tốt, nhưng trong hình ảnh mà bạn bắt đầu nhìn thấy ánh sáng xung quanh các cạnh, bạn có thể muốn chơi với một trong ba lựa chọn khác. Dark / Bright Mask Grayscale - Những tùy chọn kiểm soát của ba hình ảnh mà bạn muốn sử dụng như mặt nạ lớp cho hình ảnh tối và sáng. | Part III Manipulating Images choices are actually a bit of misnomer. All of the blurs are Gaussian blurs but the Selective option is a specific type of Gaussian blur that pays attention to edges. The default Gaussian blur without edge protection generally gives good results but in images where you start seeing glow around edges you may want to play with one of the other three options. Dark Bright Mask Grayscale These options control which of the three images you want to use as the layer mask for the dark and bright image. Typically you ll want to stick with using the defaults here but if you need to squeeze out some extra detail from some parts changing these values can help. Dark Takes Precedence When Exposure Blend finishes you ll have three layers two with masks as shown in Figure 12-16. By default the bright exposure layer is at the top of the stack. However this may yield results that are brighter than you want. You can manually move the dark exposure layer up or you can send it straight to the top here by enabling this check box. Auto-Trim Mask Histograms Enabling this option is basically the same as opening the Levels dialog and clicking the Auto button on each of the exposure masks. Scale Largest Image Dimension to Type in an image size here in pixels such as 800x600 and the tone-mapped image that comes out of Exposure Blend is proportionally scaled to be no larger than those dimensions. This is useful if you want to test some settings before applying them to full-sized images. FIGURE 12-15 The Exposure Blend dialog Once you have all the settings adjusted the way you like click the OK button and Exposure Blend will do its magic. If the source files you re using are large this step might take a while especially if you re running GIMP on an older computer. When it s complete though you have an image window with your processed results in it. The cool thing is that Exposure Blend doesn t 342 Chapter 12 Enhancing Photos give you a flattened image as your result.
