From 8ac23f05dd183d3ca54c89d9e0a6f01acab113dc Mon Sep 17 00:00:00 2001
From: David Schmenk <dschmenk@sbcglobal.net>
Date: Tue, 19 Nov 2024 10:31:00 -0800
Subject: [PATCH] Switch to dot product for closeset chroma match

---
 src/samplesrc/dcgrrgb.pla | 106 ++++++++++++++++++++++----------------
 1 file changed, 63 insertions(+), 43 deletions(-)

diff --git a/src/samplesrc/dcgrrgb.pla b/src/samplesrc/dcgrrgb.pla
index 40619b8..d6d6178 100644
--- a/src/samplesrc/dcgrrgb.pla
+++ b/src/samplesrc/dcgrrgb.pla
@@ -10,6 +10,7 @@ const RED_MSK = $7C00
 const BLU = 0
 const GRN = 1
 const RED = 2
+const ERR_MIN = 31
 byte[12] ntscCycle
 byte[] ntscChroma
 
@@ -19,15 +20,28 @@ byte[] ntscChroma
 //byte[]              =   1,  77,  64 // BROWN
 //byte[]              =  64,  20, 128 // RED
 // Imperical 0-63        B   G   R
-byte[]              = 32, 14, 16 // BLUE
-byte[]              = 16, 28,  0 // GREEN
-byte[]              =  0, 18, 16 // BROWN
-byte[]              = 16,  4, 32 // RED
+//byte[]              = 32, 14, 16 // BLUE
+//byte[]              = 16, 28,  0 // GREEN
+//byte[]              =  0, 18, 16 // BROWN
+//byte[]              = 16,  4, 32 // RED
 // Ideal/simplified 0-63 B   G   R
-//byte[]              = 32, 16, 16 // BLUE
-//byte[]              = 16, 32,  0 // GREEN
-//byte[]              =  0, 16, 16 // BROWN
-//byte[]              = 16,  0, 32 // RED
+//byte[]                = 32, 16, 16 // BLUE
+//byte[]                = 16, 32,  0 // GREEN
+//byte[]                =  0, 16, 16 // BROWN
+//byte[]                = 16,  0, 32 // RED
+// Test             0-63 B   G   R
+byte[]                = 63,  0,  0 // BLUE
+byte[]                =  0, 63,  0 // GREEN
+byte[]                =  0, 31, 31 // BROWN
+byte[]                =  0,  0, 63 // RED
+//byte[]              = 64, 28, 32 // BLUE
+//byte[]              = 32, 56,  0 // GREEN
+//byte[]              =  0, 36, 32 // BROWN
+//byte[]              = 32,  8, 64 // RED
+//byte[]                = 64, 32, 32 // BLUE
+//byte[]                = 32, 26,  0 // GREEN
+//byte[]                =  0, 32, 32 // BROWN
+//byte[]                = 32,  0, 64 // RED
 
 var er, eg, eb // Running error
 
@@ -43,55 +57,53 @@ def max(a, b)
     return a < b ?? b :: a
 end
 
+def min(a, b)
+    return a < b ?? a :: b
+end
+
+def errmin(v)
+    return v >= 0
+end
+
+def dotprod(x1, y1, z1, x2, y2, z2)
+    return X1*x2 + y1*y2 + z1*z2
+end
+
 def rgbpix(r, g, b, x, y)#0
   var cr, cg, cb, cx
-  var dr, dg, db
-  var zdist, cdist
+  var zdot, cdot
   byte i
 
   // Error propogation
-  //r = r - er/4
-  //g = g - eg/4
-  //b = b - eb/4
-  //puts("Match: "); puti(x & 3); putln
-  //puti(r); putc(',');puti(g); putc(',');puti(b); putln
-  //puts("Cycle:\n")
+  r = r + er/2
+  g = g + eg/2
+  b = b + eb/2
   cr = 0
   cg = 0
   cb = 0
-  // Sum current chroma cycle
+  // Project RGB on chroma cycle with zero current 1/4 chroma
   for cx = x - 1 downto x - 3
     i = (cx & 3) * 3
-    //puti(ntscCycle[i+RED]; putc(',')
-    //puti(ntscCycle[i+GRN]; putc(',')
-    //puti(ntscCycle[i+BLU]; putln
     cr = cr + ntscCycle[i+RED]
     cg = cg + ntscCycle[i+GRN]
     cb = cb + ntscCycle[i+BLU]
   next
-  //puts("-------------\n")
-  //puti(cr); putc(',');puti(cg); putc(',');puti(cb); putln
-  // Subtract off chroma cycle from RGB pixel
+  zdot = dotprod(r, g, b, cr, cg, cb)
+  // Save error for zero 1/4 cycle
   er = r - cr
   eg = g - cg
   eb = b - cb
-  zdist = er*er + eg*eg + eb*eb // Distance to zero (black)
+  // Add current 1/4 chroma color
   i = (x & 3) * 3
-  dr = er - ntscChroma[i+RED]
-  dg = eg - ntscChroma[i+GRN]
-  db = eb - ntscChroma[i+BLU]
-  cdist = dr*dr + dg*dg + db*db // Distance to chroma color
-  //puts("-------------\n")
-  //puti(ntscChroma[i+RED]); putc(',')
-  //puti(ntscChroma[i+GRN]); putc(',')
-  //puti(ntscChroma[i+BLU]); putln
-  //puts("Dist to Zero (Black):"); puti(zdist); putln
-  //puts("Dist to Chroma Color:"); puti(cdist); putln
-  if cdist < zdist
-    // RGB closer to chroma color
-    er = dr
-    eg = dg
-    eb = db
+  cr = cr + ntscChroma[i+RED]
+  cg = cg + ntscChroma[i+GRN]
+  cb = cb + ntscChroma[i+BLU]
+  cdot = dotprod(r, g, b, cr, cg, cb)
+  if cdot > zdot
+    // RGB better matched with 1/4 chroma color
+    er = r - cr
+    eg = g - cg
+    eb = b - cb
     ntscCycle[i+RED] = ntscChroma[i+RED]
     ntscCycle[i+GRN] = ntscChroma[i+GRN]
     ntscCycle[i+BLU] = ntscChroma[i+BLU]
@@ -102,7 +114,9 @@ def rgbpix(r, g, b, x, y)#0
     ntscCycle[i+GRN] = 0
     ntscCycle[i+BLU] = 0
   fin
-  //getc
+  //er = min(63, max(-63, er))
+  //eg = min(63, max(-63, eg))
+  //eb = min(63, max(-63, eb))
 end
 
 def rgbTest#0
@@ -111,29 +125,35 @@ def rgbTest#0
   for i = 0 to 63
     rgbpix(i, 0, 0, i, 0)
   next
+  er, eg, eb, = 0, 0, 0
   memset(@ntscCycle, 0, 12)
   for i = 0 to 63
     rgbpix(0, i, 0, i, 2)
   next
+  er, eg, eb, = 0, 0, 0
   memset(@ntscCycle, 0, 12)
   for i = 0 to 63
     rgbpix(0, 0, i, i, 4)
   next
+  er, eg, eb, = 0, 0, 0
   memset(@ntscCycle, 0, 12)
   for i = 0 to 63
     rgbpix(i, i, i, i, 6)
   next
+  er, eg, eb, = 0, 0, 0
   memset(@ntscCycle, 0, 12)
   for i = 0 to 63
-    rgbpix(i, i>>1, i>>1, i, 8)
+    rgbpix(i, i>>2, i>>2, i, 8)
   next
+  er, eg, eb, = 0, 0, 0
   memset(@ntscCycle, 0, 12)
   for i = 0 to 63
-    rgbpix(i>>1, i, i>>1, i, 10)
+    rgbpix(i>>2, i, i>>2, i, 10)
   next
+  er, eg, eb, = 0, 0, 0
   memset(@ntscCycle, 0, 12)
   for i = 0 to 63
-    rgbpix(i>>1, i>>1, i, i, 12)
+    rgbpix(i>>2, i>>2, i, i, 12)
   next
 end