From 094d5158a685a62866db24dff364c746df0f2cb4 Mon Sep 17 00:00:00 2001
From: Markus Noga <ml@noga.de>
Date: Fri, 19 Jun 2020 01:00:12 +0200
Subject: [PATCH] towards #5: experimental debayering code for RGGB color
 filter array

---
 internal/debayer.go | 155 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 155 insertions(+)
 create mode 100644 internal/debayer.go

diff --git a/internal/debayer.go b/internal/debayer.go
new file mode 100644
index 0000000..275eabf
--- /dev/null
+++ b/internal/debayer.go
@@ -0,0 +1,155 @@
+// Copyright (C) 2020 Markus L. Noga
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+
+package internal
+
+
+// Color filter array type, from top to bottom and left to right
+type CFAType int
+const (
+	CFATypeRGGB CFAType = iota
+	CFATypeGRBG
+	CFATypeGBRG
+	CFATypeBGGR
+)
+
+// Textual names for color filter array types. Indexed by CFAType
+var CFANames=[]string{"RGGB", "GRBG", "GBRG", "BGGR"}
+
+
+func DebayerBilinearToRed(data []float32, width int32, cfaType CFAType) (rs []float32, adjWidth int32) {
+	switch cfaType {
+	case CFATypeRGGB:
+		return DebayerBilinearRGGBToRed(data, width)
+	}
+	LogFatalf("Unimplemented CFA type for debayering: %d\n", cfaType)
+	return nil, 0 // never reached
+}
+
+func DebayerBilinearRGGBToRed(data []float32, width int32) (rs []float32, adjWidth int32) {
+	height   :=int32(len(data))/width
+	adjWidth  =width  & ^1            // ignore last column and row in odd-sized images
+	adjHeight:=height & ^1
+	rs        =GetArrayOfFloat32FromPool(int(adjWidth)*int(adjHeight))
+
+	// for all pixels in adjusted range
+	for row:=int32(0); row<adjHeight; row+=2 {
+		for col:=int32(0); col<adjWidth; col+=2 {
+			srcOffset :=row*width   +col
+			destOffset:=row*adjWidth+col
+
+			// read relevant red values
+			r:=data[srcOffset]
+			rRight, rDown, rRD:=r, r, r
+			if col+2<adjWidth {
+				rRight=data[srcOffset+2]
+	 			if row+2<adjHeight {
+	 				rDown=data[srcOffset+  2*width]
+	 				rRD  =data[srcOffset+2+2*width]
+	 			}			
+			} else if row+2<adjHeight {
+	 				rDown=data[srcOffset+2*width]
+			}
+
+			// interpolate and write red values
+			rs[destOffset           ]=      r
+			rs[destOffset+1         ]=0.5 *(r+rRight)
+ 			rs[destOffset  +adjWidth]=0.5 *(r+rDown)
+ 			rs[destOffset+1+adjWidth]=0.25*(r+rRight+rDown+rRD)
+		}
+	}
+
+	return rs, adjWidth
+}
+
+func DebayerBilinearRGGBToGreen(data []float32, width int32) (gs []float32, adjWidth int32) {
+	height   :=int32(len(data))/width
+	adjWidth  =width  & ^1            // ignore last column and row in odd-sized images
+	adjHeight:=height & ^1
+	gs        =GetArrayOfFloat32FromPool(int(adjWidth)*int(adjHeight))
+
+	// for all pixels in adjusted range
+	for row:=int32(0); row<adjHeight; row+=2 {
+		for col:=int32(0); col<adjWidth; col+=2 {
+			srcOffset :=row*width   +col
+			destOffset:=row*adjWidth+col
+
+			// read relevant green values
+			g1:=data[srcOffset+1      ]
+			g2:=data[srcOffset  +width]
+
+			g1Left, g2Up:=g1, 0.5*(g1+g2)
+			if col>=2 {
+				g1Left=data[srcOffset-1      ]
+	 			if row>=2 {
+	 				g2Up=data[srcOffset-1-width]
+	 			}			
+			}
+			g2Right, g1Down:=g2, 0.5*(g1+g2)
+			if col<adjWidth-2 {
+				g2Right=data[srcOffset+2+width]
+	 			if row<adjHeight-2 {
+	 				g1Down=data[srcOffset+1+2*width]
+	 			}			
+			}
+
+			// interpolate and write green values
+			gs[destOffset           ]=0.25*(g1+g2+g1Left+g2Up)
+			gs[destOffset+1         ]=      g1
+ 			gs[destOffset  +adjWidth]=         g2
+ 			gs[destOffset+1+adjWidth]=0.25*(g1+g2+g2Right+g1Down)
+		}
+	}
+
+	return gs, adjWidth
+}
+
+func DebayerBilinearRGGBToBlue(data []float32, width int32) (bs []float32, adjWidth int32) {
+	height   :=int32(len(data))/width
+	adjWidth  =width  & ^1            // ignore last column and row in odd-sized images
+	adjHeight:=height & ^1
+	bs        =GetArrayOfFloat32FromPool(int(adjWidth)*int(adjHeight))
+
+	// for all pixels in adjusted range
+	for row:=int32(0); row<adjHeight; row+=2 {
+		for col:=int32(0); col<adjWidth; col+=2 {
+			srcOffset :=row*width   +col
+			destOffset:=row*adjWidth+col
+
+			// read relevant blue values
+			b:=data[srcOffset+1+width]
+			bLeft, bUp, bLU:=b, b, b
+			if col>=2 {
+				bLeft=data[srcOffset-1+width]
+	 			if row>=2 {
+	 				bUp=data[srcOffset+1-width]
+	 				bLU=data[srcOffset-1-width]
+	 			}			
+			} else if row>=2 {
+	 				bUp=data[srcOffset+1-width]
+			}
+
+			// interpolate and write blue values
+			bs[destOffset           ]=0.25*(b+bLeft+bUp+bLU)
+			bs[destOffset+1         ]=0.5 *(b+bUp)
+ 			bs[destOffset  +adjWidth]=0.5 *(b+bLeft)
+ 			bs[destOffset+1+adjWidth]=      b
+		}
+	}
+
+	return bs, adjWidth
+}
+