Map power to HSV

spectrogram.cpp

@@ -9,6 +9,8 @@
 Spectrogram::Spectrogram()
 {
 	inputSource = new InputSource("/home/mike/Downloads/hubsan-chopped.cfile", 1024);
+	powerMax = 0.0f;
+	powerRange = 40.0f;
 	resize(inputSource->GetWidth(), inputSource->GetHeight());
 }
 
@@ -17,6 +19,62 @@ Spectrogram::~Spectrogram()
 	delete inputSource;
 }
 
+template <class T> const T& clamp (const T& value, const T& min, const T& max) {
+    return std::min(max, std::max(min, value));
+}
+
+void HSVtoRGB( float *r, float *g, float *b, float h, float s, float v )
+{
+    int i;
+    float f, p, q, t;
+
+    if( s == 0 ) {
+        // achromatic (grey)
+        *r = *g = *b = v;
+        return;
+    }
+
+    h /= 60;            // sector 0 to 5
+    i = floor( h );
+    f = h - i;          // factorial part of h
+    p = v * ( 1 - s );
+    q = v * ( 1 - s * f );
+    t = v * ( 1 - s * ( 1 - f ) );
+
+    switch( i ) {
+        case 0:
+            *r = v;
+            *g = t;
+            *b = p;
+            break;
+        case 1:
+            *r = q;
+            *g = v;
+            *b = p;
+            break;
+        case 2:
+            *r = p;
+            *g = v;
+            *b = t;
+            break;
+        case 3:
+            *r = p;
+            *g = q;
+            *b = v;
+            break;
+        case 4:
+            *r = t;
+            *g = p;
+            *b = v;
+            break;
+        default:        // case 5:
+            *r = v;
+            *g = p;
+            *b = q;
+            break;
+    }
+}
+
 void Spectrogram::paintEvent(QPaintEvent *event)
 {
 	QElapsedTimer timer;
@@ -37,8 +95,13 @@ void Spectrogram::paintEvent(QPaintEvent *event)
 		QImage image(width, height, QImage::Format_RGB32);
 		for (int y = 0; y < height; y++) {
 			for (int x = 0; x < width; x++) {
-				uint8_t pixel = data[y*width + x] * -3;
-				image.setPixel(x, y, qRgb(0, 0, pixel));
+				float normPower = (data[y*width + x] - powerMax) * -1.0f / powerRange;
+				normPower = clamp(normPower, 0.0f, 1.0f);
+
+				float red, green, blue;
+				HSVtoRGB(&red, &green, &blue, normPower * 300.0f, 1, 1 - normPower);
+
+				image.setPixel(x, y, qRgb(red * 255, green * 255, blue * 255));
 			}
 		}
 
@@ -56,4 +119,4 @@ void Spectrogram::setFFTSize(int size)
 	inputSource->setFFTSize(size);
 	update();
 	resize(inputSource->GetWidth(), inputSource->GetHeight());
-}
+}