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Rất nhiều điều! Như vừa mô tả, bạn có nhiều hơn nữa có thể có giá trị âm, mà cung cấp khả năng cụ thể chính xác hơn trong bức ảnh của bạn và mượt mà hơn quá trình chuyển đổi âm. Nhưng RAW có lợi thế khác nữa. Ví dụ, bạn có thể "phơi bày bên phải" (như chúng tôi sẽ mô tả ngắn, trong Exposure "" phần của chương này) để tối ưu hóa | 256 possible tonal values each pixel has 16.7 million 256 x 256 x 256 possible color values as shown in Table 1.1. Table 1.1 Colors and Bit Depths Bit Depth Typical Format Possible Colors per Component Possible Colors per Pixel 8 bits JPEG 256 16.7 million 12 bits RAW 4 096 68.7 billion 16 bits PSD TIFF 65 536 281 trillion 6 CHAPTER 1 THINKING DIGITALLY Now 16 million color choices may seem like more than enough but in reality at times the transitions between tones in an 8-bit image are not smooth which is called posterization or banding. Twelve-bit images which is what many cameras can capture in RAW have 4 096 tonal values for each color channel which means a choice of 68.7 billion 4 096 x 4 096 x 4 096 possible colors. Some of the newest high-end digital SLR cameras capture 14-bit images which means nearly 4.4 trillion color choices 16 384 x 16 384 x 16 384 . Tonal gradations are much smoother with so many possible values for each pixel. JPEG images are limited to 8 bits so some JPEG images may demonstrate posterization. Although not a problem for many images some images particularly those requiring smooth gradual transitions of saturated bright colors and tones such as sunset pictures may show evidence of banding. Clearly more detail can be accurately conveyed the higher the bit depth. Eight-bit color files used to be common but 16-bit images are now the standard for most photographers. Thirty-two-bit files are starting to emerge and can be created using Photoshop s Merge to HDR which we ll cover in Chapter 8. HDR stands for high dynamic range. It may seem confusing initially that in Photoshop you have options to choose 8-bit or 16-bit images or 32-bit if you ve created an HDR image when a JPEG image is clearly an 8-bit file and a raw file is either a 12- or 14-bit file. Converting a 12-bit capture into an 8-bit file results in a smaller file in which you have discarded 3 840 possible tonal values per color channel and even more if the image was a 14-bit file.
