灰度到红绿蓝（MATLAB Jet）色标 [英] Grayscale to Red-Green-Blue (MATLAB Jet) color scale

问题描述

我得到一个本质上是图像的数据集，但图像中的每个像素都表示为-1到1（包括1和1）的值。我编写一个应用程序，需要采取这些-1到1灰度值，并将它们映射到MATLABJet颜色标度（红 - 绿 - 蓝色渐变）的相关联的RGB值。

I was given a data set that is essentially an image, however each pixel in the image is represented as a value from -1 to 1 inclusive. I am writing an application that needs to take these -1 to 1 grayscale values and map them to the associated RGB value for the MATLAB "Jet" color scale (red-green-blue color gradient).

我很好奇，如果有人知道如何取一个线性值（如-1到1），并将其映射到这个比例。注意，我实际上并不使用MATLAB（我也不能），我只需要把灰度值并把它放在Jet梯度。

I am curious if anyone knows how to take a linear value (like -1 to 1) and map it to this scale. Note that I am not actually using MATLAB for this (nor can I), I just need to take the grayscale value and put it on the Jet gradient.

谢谢，
Adam

Thanks, Adam

推荐答案

我希望这是您要找的：

double interpolate( double val, double y0, double x0, double y1, double x1 ) {
  return (val-x0)*(y1-y0)/(x1-x0) + y0;
}
double blue( double grayscale ) {
  if ( grayscale < -0.33 ) return 1.0;
  else if ( grayscale < 0.33 ) return interpolate( grayscale, 1.0, -0.33, 0.0, 0.33 );
  else return 0.0;
}
double green( double grayscale ) {
  if ( grayscale < -1.0 ) return 0.0; // unexpected grayscale value
  if  ( grayscale < -0.33 ) return interpolate( grayscale, 0.0, -1.0, 1.0, -0.33 );
  else if ( grayscale < 0.33 ) return 1.0;
  else if ( grayscale <= 1.0 ) return interpolate( grayscale, 1.0, 0.33, 0.0, 1.0 );
  else return 1.0; // unexpected grayscale value
}
double red( double grayscale ) {
  if ( grayscale < -0.33 ) return 0.0;
  else if ( grayscale < 0.33 ) return interpolate( grayscale, 0.0, -0.33, 1.0, 0.33 );
  else return 1.0;
}

我不知道这个比例是100％但它应该看起来很相似。

I'm not sure if this scale is 100% identical the image you linked but it should looks very similar.

UPDATE
我根据MatLab的Jet调色板的描述重写代码这里

double interpolate( double val, double y0, double x0, double y1, double x1 ) {
    return (val-x0)*(y1-y0)/(x1-x0) + y0;
}

double base( double val ) {
    if ( val <= -0.75 ) return 0;
    else if ( val <= -0.25 ) return interpolate( val, 0.0, -0.75, 1.0, -0.25 );
    else if ( val <= 0.25 ) return 1.0;
    else if ( val <= 0.75 ) return interpolate( val, 1.0, 0.25, 0.0, 0.75 );
    else return 0.0;
}

double red( double gray ) {
    return base( gray - 0.5 );
}
double green( double gray ) {
    return base( gray );
}
double blue( double gray ) {
    return base( gray + 0.5 );
}

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