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设计说明
The S-Log gamma function is optimized for Digital Motion Picture camera. The logarithmic camera encoding curve was carefully designed by analyzing the noise floor characteristics and the tonal reproduction of the imaging device. Since negative film stock and the CCD or CMOS imager behave differently to incoming light, especially in the low-light and high-light region, the S-Log curve differs from Log curves for film based images. CCD or CMOS imagers respond to incoming light in a far more linear fashion than film, thus there are no “toes” or “shoulders”. The S-Log curve provides sufficient quantization bits to offer exceptional tonal reproduction in both the low-light and high-light region. The appearance on a monitor is also taken into consideration, so that an S-Log image could be viewed using an appropriate display LUT (Film Print Emulation and/or S-Log to Rec 709). When shooting in S-Log, as distinct from ITU-R BT. 709 (Rec 709) video gamma, a color grading (‘look management’) process is mandatory to establish a desired reference ‘look’ (color; contrast) for dailies and editorial. This color graded ’look’ should be related to a target output display, e.g., film print projection; digital cinema projection. When viewing S-Log encoded images on an HD reference monitor that are ultimately intended for cinema release via film print and D-cinema projection, a display LUT should be applied that emulates film print or digital cinema color and contrast within the constraints of the video monitor’s gamut and contrast. Using the traditional photo-chemical analogy, S-Log is the “camera negative” and the final look of the “release print” and DCP is ultimately defined during the final color grading in the Digital Intermediate post production process.
和其他Log一样，Slog整个系列的设计初衷是为优化数字传感器的编码体系的，并在阴影和高光的资源分配间取得平衡，同时最大程度利用传感器的动态范围。
注意，Slog提出也有让数字摄影机画面适配Cineon工作流程的初衷，Arri LogC 在设计时也有考虑这一点。
Slog3的提出
F65, F55 and F5 will add two new color grading spaces, “S-Gamut3.Cine/S-Log3” and “S- Gamut3/S-Log3”. This document provides a technical summary of the new color grading space for people who are familiar with Log Base Grading. “S-Gamut3.Cine/S-Log3” is designed for more like pure log workflow. Color space is similar to negative film scan which is used for TV production, film out and digital cinema. Color reproduction is designed slightly wider than DCI-P3 to provide ample room of grading. Tone curve is more like pure log encoding characteristics preserving more tonal gradations in the blacks, and has good compatibility with Cineon workflow. “S-Gamut3/S-Log3” is very close to camera native color, and is very good for archiving as a digital camera negative, as 8/10/12bit code value. Color space of S-Gamut3 is kept the same area of original S-Gamut, though color reproduction inside S-Gamut3 is more accurate than S- Gamut.
这里提到S-Log3” is designed for more like pure log workflow. 即Slog3比前代「更加对数」，整个曲线更加平滑
我们还能注意到 S-Gamut3设计时考虑了摄影机的本身色彩特性，可以说是量身定制，能够最大程度保留信息。
Why S-Gamut3.Cine
S-Gamut3.Cine is similar to negative film scan which was used for TV production, film out digital cinema. Color reproduction is designed slightly wider than DCI-P3 to provide ample room for grading. Thus manual grading for P3 becomes easier. S-Gamut3.Cine is more convenient to grade than S-Gamut3 and S-Gamut as camera digital negative. If you would like to apply print film emulation, please increase saturation to about 1.4. Sony also provides .cube files (Look Profile) to convert 709 video color space.
乍一看这句话说的很抽象，不过当我们把这两个Gamut放到CIExy图上之后，就一目了然了！
能够很好的发现， Cine更靠近DCI-P3的的外形，因此在基于P3的手工调色流程中，调色师会获得更加适应的体验。
例如，可以直接通过Channal Mixer工具来实现一个饱和度变化，同时画面的颜色变化更加自然（不过有CMS系统介入，其实这两个空间也没有那么大的区别了）
另一方面，S-Gamut3与S-Gamut外形一致，更适合在BT.2020以及SMPTE2065-1(ACES)流程中使用，而且简化了颜色转换矩阵
Current S-Gamut needs color temperature setting to select color conversion matrix. But S-Gamut3 is optimized to combine these color conversion matrix. The conversion matrix does not depend on color temperature any more.
懂得都懂
Slog2 vs Slog3
Slog3通过给亮区分配更少的码值，实现暗部更加平直的记录，因此能获得更好的暗部对比度。这也是为什么许多用户「感知」在使用Slog3时画面出现了更大噪声，其实这个感觉是错误的，只是因为Slog3将暗部细节扩展了。在两种曲线都Mapping到Rec709时，用户便会发现他们的质量都「差不多」，原来是噪声的区域变成了黑色，即压缩状态。
不过如果在S-Log3模式出现一大堆噪点，更应该考虑自己的曝光状态，以及自己的设备是不是已经“准备好了”，去迎接S-log3这条曲线，毕竟，一些旧传感器的确在暗部表现不佳，使用了S-log3之后弱点就更明显了！
Legal OR Full？
Is S-Log3 Full (Extended) range or Legal range?
A4. S-Log3 is recorded as Full range in XAVC, MPEG and HDCAM SR File. Camera SDI output is also Full range every time. There is no option to select Legal range to prevent miss operation. Full (Extended) range: Data range is used from 0 to 1023 (from -7IRE to 109IRE) to utilize full 10bit code value. SDI treat valid data from 4 to 1019, but definition of Full (Extended) does not change between file and SDI.
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