C++ sRGB<-&燃气轮机；线性RGB转换精度

我试图理解图像/视频处理的基础知识，最近我了解到所有的处理都应该应用于图像的线性表示。因此，我为sRGB->RGB和RGB->sRGB编写了两个函数：

void sRGB2lRGB(std::vector<unsigned char>& in, std::vector<unsigned char>& out)
{
    std::vector<double> temp(in.begin(), in.end());

    for (int i = 0; i < temp.size(); i++)
    {
        temp[i] /= 255.0;
    }

    for (int i = 0; i < temp.size(); i++)
    {
        if (temp[i] <= 0.04045)
        {
            temp[i] /= 12.92;
        }
        else
        {
            temp[i] = std::pow((temp[i] + 0.055) / 1.055, 2.4);
        }
    }

    for (int i = 0; i < temp.size(); i++)
    {
        out[i] = temp[i] * (int)255 + 0.5;
    }
}

void lRGB2sRGB(std::vector<unsigned char>& in, std::vector<unsigned char>& out)
{
    std::vector<double> temp(in.begin(), in.end());

    for (int i = 0; i < temp.size(); i++)
    {
        temp[i] /= 255.0;
    }

    for (int i = 0; i < temp.size(); i++)
    {
        if (temp[i] <= 0.0031308)
        {
            temp[i] *= 12.92;
        }
        else
        {
            temp[i] = 1.055 * std::pow(temp[i], 1.0 / 2.4) - 0.055;
        }
    }

    for (int i = 0; i < temp.size(); i++)
    {
        out[i] = temp[i] * (int)255 + 0.5;
    }
}

---

我错在哪里？

因为您通过将线性浮点值转换为整数表示来量化它们，所以转换确实是破坏性的

然而，出现这种情况并不奇怪：这实际上是使用sRGB逆电光传递函数（EOTF）编码数据时的意图。其目的是通过8位信号传输数据，同时保持良好的感知一致性，总体带宽降低

我会参考查尔斯·波因顿和波因顿，C.&芬特，B.（2014）。数字图像表示和显示的感知一致性。色彩研究与应用，39（1），6-15

---

请注意，此处的“对话”应为“转换”。

在

sRGB2lRGB

中，对于小于7的所有输入值，您对

out[i]

的计算将为0，因此在尝试反向计算时，您将获得相同的值。看起来这是线性空间的一个功能，但是，由于black附近的信息基本上丢失了，我看不出该对话是如何恢复的：/

int main()
{
    std::vector<unsigned char> in(255);
    std::vector<unsigned char> out(255);
    std::vector<unsigned char> out2(255);

    for (int i = 0; i < 255; i++)
    {
        in[i] = i;
    }

    sRGB2lRGB(in, out);
    lRGB2sRGB(out, out2);

    for (int i = 0; i < 255; i++)
    {
        if (out2[i] != i)
        {
            std::cout << "was: " << (int)in[i] << ", now: " << (int)out2[i] << '\n';
        }
    }
}

was: 1, now: 0
was: 2, now: 0
was: 3, now: 0
was: 4, now: 0
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