tailieunhanh - Photoshop cs5 cho nhiếp ảnh gia part 4

Giải thích thông Histograms Một số người nhầm lẫn nghĩ rằng một biểu đồ lý tưởng sẽ là một phân phối hình chuông của điểm ảnh. Trong thực tế, có không phải là một biểu đồ lý tưởng duy nhất cho tất cả hình ảnh. | Figure A histogram for this shade of purple which has RGB values of 132 0 189 shows that the luminosity histogram has a single line at 60 whereas the RGB histogram is composed of three lines one at 0 one at 132 and one at 189. 14 CHAPTER 1 THINKING DIGITALLY Which type of histogram should you use That depends on several things including what information is most helpful for gauging the exposure of a particular image as well as what histogram options your camera offers. It used to be that most cameras offered only one or the other type of histogram however some of the newer models offer a choice. What s most important is to be aware of what type of histogram you re viewing so you will understand precisely what the data is saying. Interpreting Histograms Some people mistakenly think that an ideal histogram would be a bell-shaped distribution of pixels. In fact there s not a single ideal histogram for all images. The histogram just reflects the tones in the scene that you are capturing given that particular exposure setting. The ideal exposure for most scenes will yield a histogram that indicates all the data has been captured without any clipping. Let s look at a series of pictures and their histograms. Figure shows a good histogram for an average scene with a full range of tonalities. Note that the pixels extend across the entire histogram but there are no spikes at either end. Spikes at the ends would mean you have pixels that are overexposed or underexposed and therefore areas with no detail. Since all the pixels fall within the bounds of the histogram this picture will have detail throughout. Figure shows an underexposed picture. Most of the pixels are in the left portion of the histogram indicating no light tones. Since you know that part of the pelican is in fact white a proper exposure would have the pixel distribution moved to the right. If you are shooting a subject with a large light area and you see a histogram that looks like Figure you