还有，用什么仪器测，哪个位置测合适？光照度多少合适？先谢谢

正好这两天在研究这个。

sRGB 标准的编码（对我们来说就是修图）的环境照度是 64 Lux。假定的观看亮度是 200 Lux （普通办公室环境）。

修图的时候最好不要有灯光照在屏幕上，最好是灯光照在屏幕后方。

测量仪器淘宝上买个照度计就行，100元左右。测量时可以将显示器关闭，将探头同眼睛的位置和方向保持一致。

另外 sRGB 推荐的屏幕亮度是 80 cd/m^2，一般可以在80-120之间，这个可以用校色仪测量，校色仪稍贵。

环境亮度会影响人对对比度的感觉，比如 16 lux 环境下用 gamma 2.4 显示器看到的图片， 同 64 lux 环境下 gamma 2.2 显示器看到的同一张图片，视觉效果是相同的。 也就是说如果不改变显示器参数，环境光较暗时，修图时会有将对比度调高的倾向。

当然这些都是高一些的要求，一般人可能不会考虑这些。比如分别在 16 lux 和 64 lux 环境下将某张图修成一个感觉，gamma 值偏差也只有 0.2，虽然可以察觉出来，但是对普通照片来说，对比度增加减少那么一点可能都不影响欣赏。如果想感受下 0.2 的 gamma 值具体是多大，可以到显卡设置界面，把 gamma 值增加或减少 0.2 来感觉一下。

下面引用自 sRGB 标准 （https://www.w3.org/Graphics/Color/sRGB.html）

“Viewing Gamma

The reason that a viewing gamma of 1.125 is used instead of 1.0 is to compensate for the viewing environment conditions, including ambient illumination and flare. Historically, viewing gammas of 1.5 have been used for viewing projected slides in a dark room and viewing gammas of 1.25 have been used for viewing monitors in a very dim room. This very dim room value of 1.25 has been used extensively in television systems and assumes a ambient luminance level of approximately 15 lux. The current proposal assumes an encoding ambient luminance level of 64 lux which is more representative of a dim room in viewing computer generated imagery. Such a system assumes a viewing gamma of 1.125 and is thus consistent with the 709 standard described below. While we believe that the typical office or home viewing environment actually has an ambient luminance level around 200 lux, we found it impractical to attempt to account for the resulting large levels of flare that resulted. In addition, recent work by the ISO JTAG2 standards committee supports the ambient luminance level of 64 lux.

If the viewing condition is different from the standard, then the decoding process must compensate. This can be done by modifying the gamma values in equation 1.2 below by the appropriate factor. If one does modify the gamma values in equation 1.2 below, extreme care must be taken to avoid quantization errors when working with 24 bit images and high viewing flare levels.

The ITU-R BT.709 transfer function in combination with its target monitor is attempting to achieve a viewing gamma of 1.125 by incorrectly assuming a CRT gamma of 2.5 and an LUT gamma of 1.0/2.222 as shown in the equation below. The justification of a viewing gamma value of 1.125 is described below in the section on viewing environment compensation.

illustration (0.3)

Using the actual power function fit value for the 709 transfer function of 1.0/1.956 and maintaining the display gamma of 1.125, we can solve for the ideal target monitor gamma of 2.2. This is consistent with the CRT gamma value proposed in this paper. ”
本帖最后由 jetair 于 2017-10-17 16:29 编辑

那就买个色温表呗，色温照度都能测，一般100勒克斯的照度，就特么老亮了

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