指定用于有序值的 RGB 调色板

发布于 2024-12-12 03:17:04 字数 677 浏览 0 评论 0原文

我有一个函数 f(x,y)，主要是单调的，它产生范围为 {0.0 .. 100.0} 的一些值。我想使用不同的颜色将它们绘制为二维图片，其中 (x,y) 是坐标，不同的颜色代表函数的不同值。问题如下：我不知道如何将该函数的值映射到 RGB 颜色空间并保留顺序（明显）。我已经发现了。喜欢：

R = f(x,y) * 10.0f;
G = f(x,y) * 20.0f;
B = f(x,y) * 30.0f;
color = B<<16|G<<8|R; //@low-endian

效果很好，但生成的图片太暗。如果我增加这些常量，事情并不会变得更好，因为在某些时刻，颜色分量将大于 0xFF，因此它会溢出（一个颜色分量应该在 {0 .. 0xFF} 范围内。

你知道吗？如何将值从 {0.0 .. 100.0} 映射到
RGB=[{0 .. 0xFF}<<16|{0 .. 0xFF}<<8|{0 .. 0xFF}] 这样得到的 RGB 值是可见的？

PS：也许你知道，在网上哪里可以找到更多相关理论的信息？我只记得 Foley/Van Dam 的 Comp.Graphics，但我没有这本书。

更新：我正在寻找如何生成像右边这样的色度调色板：在此处输入图像描述

原文

I have a function f(x,y), mostly monotonic, which produces some values in the range {0.0 .. 100.0}. I would like to draw them using different colors as a 2D picture, where (x,y) are coordinates and where distinctive colors stand for distinctive values of the function. The problem is following: I don't know how to map the values of this function to RGB color space preserving the order (visibly). I have found that smth. like:

R = f(x,y) * 10.0f;
G = f(x,y) * 20.0f;
B = f(x,y) * 30.0f;
color = B<<16|G<<8|R; //@low-endian

works fine, but the resulting picture is too dark. If I increase these constants, it makes things not better, because at some moment a color component will be greater than 0xFF, so it will overflow (one color component should be in the range {0 .. 0xFF}.

Do you have any idea how to map values from {0.0 .. 100.0} to
RGB=[{0 .. 0xFF}<<16|{0 .. 0xFF}<<8|{0 .. 0xFF}] so that the resulting RGB values are visibly Ok?

PS: maybe you know, where to find more info about related theory online? I remember only Comp.Graphics by Foley/Van Dam, but I don't have this book.

UPDATE: I am looking for how to generate a chroma palette like one on the right:
enter image description here

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满地尘埃落定 2024-12-19 03:17:04

您可以尝试将值限制为最大值 255 (0xff)。

R = min((int)(f(x,y) * 10.0f), 0xff);
G = min((int)(f(x,y) * 20.0f), 0xff);
B = min((int)(f(x,y) * 30.0f), 0xff);

编辑：有很多不同的方法可以自动转换为颜色，但您可能会发现它们都不能生成您正在寻找的确切进展。由于您已经有了可接受的调色板图片，一种方法是创建 256 种颜色的查找表。

#define RGB(R,G,B) (B<<16|G<<8|R)

int palette[256] = { RGB(0,0,0), RGB(0,0,128), ... };

int greyscale = (int)(f(x,y) * 2.559999);
assert(greyscale >= 0 && greyscale <= 255);
int rgb = palette[greyscale];

如果查找表太麻烦，您还可以将灰度范围分成不同的子范围，并在每个范围的端点之间进行线性插值。

int interpolate(int from, int to, double ratio)
{
    return from + (int)((to - from) * ratio); 
}
if (greyscale <= 48)
{
    R = 0;
    G = 0;
    B = interpolate(0, 255, greyscale/48.0);
}
else if (greyscale <= 96)
{
    R = 0;
    G = interpolate(0, 255, (greyscale-48)/48.0);
    B = interpolate(255, 0, (greyscale-48)/48.0);
}
else if ...

You could just try clamping the values to a maximum of 255 (0xff).

R = min((int)(f(x,y) * 10.0f), 0xff);
G = min((int)(f(x,y) * 20.0f), 0xff);
B = min((int)(f(x,y) * 30.0f), 0xff);

Edit: There are a lot of different ways to convert to colors automatically, but you might find that none of them generates the exact progression you're looking for. Since you already have a picture of an acceptable palette, one method would be to create a lookup table of 256 colors.

#define RGB(R,G,B) (B<<16|G<<8|R)

int palette[256] = { RGB(0,0,0), RGB(0,0,128), ... };

int greyscale = (int)(f(x,y) * 2.559999);
assert(greyscale >= 0 && greyscale <= 255);
int rgb = palette[greyscale];

If the lookup table is too much trouble, you could also break the greyscale range into different subranges and do a linear interpolation between the endpoints of each range.

int interpolate(int from, int to, double ratio)
{
    return from + (int)((to - from) * ratio); 
}
if (greyscale <= 48)
{
    R = 0;
    G = 0;
    B = interpolate(0, 255, greyscale/48.0);
}
else if (greyscale <= 96)
{
    R = 0;
    G = interpolate(0, 255, (greyscale-48)/48.0);
    B = interpolate(255, 0, (greyscale-48)/48.0);
}
else if ...

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