如何渲染彩虹光譜？

Question

我有必要以編程方式生成一道彩虹光譜的逼近，矩形圖像中，如下圖所示：

我知道如何繪製的像素圖，就是我正在尋找的是如何生成顏色的值。

Answer 1

您需要登錄到read this paper。認真。

除此之外，它可能需要的是使用QColor::fromHslF(x/*0.8, 0.95, 0.5)在HSL顏色表示中迭代色相，其中x在彩虹上從0.0變化到1.0。這在物理上並不準確，但也許它會這樣做。

否則，您需要一個稍微更復雜的代碼，它非常簡單地近似上面引用的論文。

#include <QApplication> 
#include <QPainter> 
#include <QPixmap> 
#include <QLabel> 
#include <algorithm> 
#include <cmath> 

QColor wavelengthToColor(qreal lambda) 
{ 
    // Based on: http://www.efg2.com/Lab/ScienceAndEngineering/Spectra.htm 
    // The foregoing is based on: http://www.midnightkite.com/color.html 
    struct Color { 
     qreal c[3]; 
     QColor toColor(qreal factor) const { 
      qreal const gamma = 0.8; 
      int ci[3]; 
      for (int i = 0; i < 3; ++i) { 
       ci[i] = c[i] == 0.0 ? 0.0 : qRound(255 * pow(c[i] * factor, gamma)); 
      } 
      return QColor(ci[0], ci[1], ci[2]); 
     } 
    } color; 
    qreal factor = 0.0; 

    static qreal thresholds[] = { 380, 440, 490, 510, 580, 645, 780 }; 
    for (unsigned int i = 0; i < sizeof(thresholds)/sizeof(thresholds[0]); ++ i) { 
     using std::swap; 
     qreal t1 = thresholds[i], t2 = thresholds[i+1]; 
     if (lambda < t1 || lambda >= t2) continue; 
     if (i%2) swap(t1, t2); 
     color.c[i % 3] = (i < 5) ? (lambda - t2)/(t1-t2) : 0.0;; 
     color.c[2-i/2] = 1.0; 
     factor = 1.0; 
     break; 
    } 

    // Let the intensity fall off near the vision limits 
    if (lambda >= 380 && lambda < 420) { 
     factor = 0.3 + 0.7*(lambda-380)/(420 - 380); 
    } 
    else if (lambda >= 700 && lambda < 780) { 
     factor = 0.3 + 0.7*(780 - lambda)/(780 - 700); 
    } 
    return color.toColor(factor); 
} 

QPixmap rainbow(int w, int h) 
{ 
    QPixmap pm(w, h); 
    QPainter p(&pm); 
    qreal f1 = 1.0/400; 
    qreal f2 = 1.0/780; 
    for (int x = 0; x < w; ++ x) { 
     // Iterate across frequencies, not wavelengths 
     qreal lambda = 1.0/(f1-(x/qreal(w)*(f1-f2))); 
     p.setPen(wavelengthToColor(lambda)); 
     p.drawLine(x, 0, x, h); 
    } 
    return pm; 
} 

class RainbowLabel : public QLabel { 
protected: 
    void resizeEvent(QResizeEvent *) { 
     setPixmap(rainbow(width(), height())); 
    } 
}; 

int main(int argc, char *argv[]) 
{ 
    QApplication a(argc, argv); 
    RainbowLabel l; 
    l.resize(600, 100); 
    l.show(); 
    return a.exec(); 
}