Mở rộng Dynamic Range Cho đến gần đây, phạm vi năng động, hay vĩ độ phơi sáng, chúng ta có thể nắm bắt trong một hình ảnh duy nhất được giới hạn bởi công nghệ máy ảnh và phim. thường xuyên, đặc biệt là trong những giờ trưa, đã có quá nhiều tương phản để có thể nắm bắt trong một shot duy nhất. Chúng tôi đã phải lựa chọn từ bỏ chi tiết trong những điểm nổi bật, bóng tối, hoặc cả hai. | 308 CHAPTER 8 COMPOSITES Expanding Dynamic Range Until recently the dynamic range or exposure latitude that we could capture in a single image was limited by camera and film technology. Often especially during the midday hours there was too much contrast to be able to capture in a single shot. We had to choose to give up detail in the highlights the shadows or both. Photoshop enables us to combine several images of the same subject taken using different exposures to retain detail in the highlights and shadows while simultaneously having the midtones properly exposed. It s almost magical how we can create an image that reflects what we actually saw no longer limited by the exposure latitude of film. There are two approaches that we ll describe to extend the exposure latitude in an image. One that we call the Cookbook approach is partially manual. The other takes full advantage of the completely revised and impressive HDR tool in CS5. Although you could simply stack two images a light one and a darker version of the same image and use a layer mask to reveal whichever layer is better exposed it s rare in nature photography to encounter situations where that will be the best approach. That works only if the areas that are exposed differentially have discrete boundaries that are easy to mask. It s better to use one of the two approaches we describe here. First we offer some hints on how best to photograph a contrasty situation so that you can easily combine the shots in Photoshop. Shooting to Expand Latitude When you encounter a situation in which there is too much contrast to capture detail in the entire scene in a single shot take several shots at different exposure levels to combine later in Photoshop and keep these suggestions in mind Use a tripod and take your first shot exposing for the shadow areas. Check your in-camera histogram to ensure that the shadow areas do not spike against the left side of the histogram. If they do take another shot adding more light to
