Photoshop Lab Color- P3: LAB has a reputation for enormous power, yet virtually all reference materials that advocate its use illustrate its capabilities with a single class of image. This chapter introduces the basic LAB correction method and explains why it is so extraordinarily effective. if you happen to have a picture of a canyon. | It s All About the Center Point 61 neutrality not every point we look at will be 0A0B. Some may appear neutral but should properly be blue others red and so forth. But our suspicions will be confirmed if all the points in nominally gray areas turn out to have cold values negative numbers in the A and B. That s how it turns out. The lightest significant point of the image is at the center of the snow nearest to us. I found this out by using the Image Adjustments Threshold command described in the box below. The average of several points in that light area is 79L 10 A 5 B. The darkest significant point is under the bridge at left. Its average reading is 27L 6 A 15 B. Interpretation the endpoints should be more like 97L and 6L. So the highlight is much too dark and the shadow much too light and the image is very flat. Colorwise the AB readings show a green cast in the highlights since in the lightest area the magenta-green A channel is considerably more negative than the yellow-blue B. In the shadow the cast is apparently more of a blue-green. The White Point and the Threshold Before applying curves we need to find the lightest and darkest points in the image. In Figure it s clear not only that the snow is the lightest part but also that its lightest area is in the center of the image. Yet when working with something as flat as Figure it s often hard to pick out the light point. Many people like to find light and dark points by using the Image Adjustments Threshold command. This command changes the image into two colors only black and white. A slider controls where the break takes place everything lighter than the slider point becomes white and everything darker black. To find the darkest points of an image therefore open the Threshold command and with Preview checked move the slider to the left until almost all the image is white. If there s any difficulty recalling what areas the dark parts now represent click OK and then toggle back and forth between the
