Add bias value to image dithering

Author: TheHans255

src/include/Image.h

@@ -110,7 +110,7 @@ class Image : virtual public NetworkClient, virtual public Adafruit_GFX
 
     void getPointsForPosition(const Position &position, const uint16_t imageWidth, const uint16_t imageHeight,
                               const uint16_t screenWidth, const uint16_t screenHeight, uint16_t *posX, uint16_t *posY);
-    uint8_t findClosestPalette(uint32_t c);
+    uint8_t findClosestPalette(uint32_t c, uint16_t bias);
 
   private:
     virtual void startWrite(void) = 0;
@@ -202,4 +202,4 @@ class Image : virtual public NetworkClient, virtual public Adafruit_GFX
     // -------------------------------------------
 };
 
-#endif
+#endif

src/include/ImageBMP.cpp

@@ -112,7 +112,7 @@ void Image::readBmpHeader(uint8_t *buf, bitmapHeader *_h)
 
 #if defined(ARDUINO_INKPLATECOLOR)
             c = c >> 8;
-            palette[i >> 1] |= findClosestPalette(c) << (i & 1 ? 0 : 4);
+            palette[i >> 1] |= findClosestPalette(c, 0) << (i & 1 ? 0 : 4);
             ditherPalette[i] = c;
 #else
             uint8_t r = (c & 0xFF000000) >> 24;
@@ -411,13 +411,6 @@ void Image::displayBmpLine(int16_t x, int16_t y, bitmapHeader *bmpHeader, bool d
                     val = RGB3BIT(r, g, b);
 #endif
             }
-
-#if defined(ARDUINO_INKPLATECOLOR) || defined(ARDUINO_INKPLATE2) || defined(ARDUINO_INKPLATE4) ||                      \
-    defined(ARDUINO_INKPLATE7)
-            val = findClosestPalette((r << 16) | (g << 8) | (b));
-#else
-            val = RGB3BIT(r, g, b);
-#endif
             writePixel(x + j, (h - y - 1), val);
             break;
         }
@@ -439,7 +432,7 @@ void Image::displayBmpLine(int16_t x, int16_t y, bitmapHeader *bmpHeader, bool d
             {
 #if defined(ARDUINO_INKPLATECOLOR) || defined(ARDUINO_INKPLATE2) || defined(ARDUINO_INKPLATE4) ||                      \
     defined(ARDUINO_INKPLATE7)
-                val = findClosestPalette((r << 16) | (g << 8) | (b));
+                val = findClosestPalette((r << 16) | (g << 8) | (b), 0);
 #else
                 val = RGB3BIT(r, g, b);
 #endif
@@ -474,7 +467,7 @@ void Image::displayBmpLine(int16_t x, int16_t y, bitmapHeader *bmpHeader, bool d
             {
 #if defined(ARDUINO_INKPLATECOLOR) || defined(ARDUINO_INKPLATE2) || defined(ARDUINO_INKPLATE4) ||                      \
     defined(ARDUINO_INKPLATE7)
-                val = findClosestPalette((r << 16) | (g << 8) | (b));
+                val = findClosestPalette((r << 16) | (g << 8) | (b), 0);
 #else
                 val = RGB3BIT(r, g, b);
 #endif
@@ -578,4 +571,4 @@ bool Image::drawBmpFromSdAtPosition(const char *fileName, const Position &positi
     }
 
     return 1;
-}
+}

src/include/ImageDitherColor.cpp

@@ -53,18 +53,32 @@ static unsigned int width = E_INK_WIDTH, height = E_INK_HEIGHT;
  * @param       uint32_t c
  *              color of the given pixel
  *
+ * @param       uint16_t bias
+ *              an arbitrary value used to break ties, should be different
+ *              for neighboring pixels, and should ideally be random
+ *
  * @return      closest color in pallete array
  */
-uint8_t Image::findClosestPalette(uint32_t c)
+uint8_t Image::findClosestPalette(uint32_t c, uint16_t bias)
 {
-    int mi = 0;
-    for (int i = 1; i < sizeof pallete / sizeof pallete[0]; ++i)
+    int32_t minDistance = 0x7fffffff;
+    uint8_t contenderCount = 0;
+    uint8_t contenderList[sizeof pallete / sizeof pallete[0]];
+
+    for (int i = 0; i < sizeof pallete / sizeof pallete[0]; ++i)
     {
-        if (COLORDISTSQR(c, pallete[i]) < COLORDISTSQR(c, pallete[mi]))
-            mi = i;
+        int32_t currentDistance = COLORDISTSQR(c, pallete[i]);
+        if (currentDistance < minDistance) {
+            minDistance = currentDistance;
+            contenderList[0] = i;
+            contenderCount = 1;
+        } else if (currentDistance == minDistance) {
+            contenderList[contenderCount] = i;
+            contenderCount++;
+        }
     }
 
-    return mi;
+    return contenderList[bias % contenderCount];
 }
 
 /**
@@ -100,7 +114,7 @@ uint8_t Image::ditherGetPixelBmp(uint32_t px, int i, int j, int w, bool paletted
     g = max((int16_t)0, min((int16_t)255, g));
     b = max((int16_t)0, min((int16_t)255, b));
 
-    int closest = findClosestPalette(((uint32_t)r << 16) | ((uint32_t)g << 8) | ((uint32_t)b));
+    int closest = findClosestPalette(((uint32_t)r << 16) | ((uint32_t)g << 8) | ((uint32_t)b), i + j);
 
     int32_t rErr = r - (int32_t)((pallete[closest] >> 16) & 0xFF);
     int32_t gErr = g - (int32_t)((pallete[closest] >> 8) & 0xFF);

src/include/ImageJPEG.cpp

@@ -390,7 +390,7 @@ bool Image::drawJpegChunk(int16_t x, int16_t y, uint16_t w, uint16_t h, uint16_t
             }
             else
             {
-                val = _imagePtrJpeg->findClosestPalette(((uint32_t)r << 16) | ((uint32_t)g << 8) | ((uint32_t)b));
+                val = _imagePtrJpeg->findClosestPalette(((uint32_t)r << 16) | ((uint32_t)g << 8) | ((uint32_t)b), 0);
             }
 
             _imagePtrJpeg->writePixel(x + i, y + j, val);
@@ -421,4 +421,4 @@ bool Image::drawJpegChunk(int16_t x, int16_t y, uint16_t w, uint16_t h, uint16_t
 #endif
 
     return 1;
-}
+}

src/include/ImagePNG.cpp

@@ -77,7 +77,7 @@ void pngle_on_draw(pngle_t *pngle, uint32_t x, uint32_t y, uint32_t w, uint32_t
                     b = 255 - b;
                 }
 
-                uint8_t px = _imagePtrPng->findClosestPalette((r << 16) | (g << 8) | (b));
+                uint8_t px = _imagePtrPng->findClosestPalette((r << 16) | (g << 8) | (b), (_pngX + x + i) + (_pngY + y + j));
 #else
                 uint8_t px = RGB3BIT(r, g, b);
 #endif
@@ -403,4 +403,4 @@ bool Image::drawPngFromSdAtPosition(const char *fileName, const Position &positi
     _pngPosition = _npos;
 
     return ret;
-}
+}