diff --git a/colormatrix.go b/colormatrix.go
index f86fa2bdc..e04bda607 100644
--- a/colormatrix.go
+++ b/colormatrix.go
@@ -27,6 +27,8 @@ const ColorMatrixDim = 5
 // while an Image's pixels' format is alpha premultiplied.
 // Before applying a matrix, a color is un-multiplied, and after applying the matrix,
 // the color is multiplied again.
+//
+// The initial value is identity.
 type ColorMatrix struct {
 	// es represents elements.
 	es *[ColorMatrixDim - 1][ColorMatrixDim]float64
@@ -41,13 +43,6 @@ func colorMatrixEsI() *[ColorMatrixDim - 1][ColorMatrixDim]float64 {
 	}
 }
 
-// NewColorMatrix returns an identity color matrix.
-func NewColorMatrix() ColorMatrix {
-	return ColorMatrix{
-		es: colorMatrixEsI(),
-	}
-}
-
 func (c ColorMatrix) dim() int {
 	return ColorMatrixDim
 }
diff --git a/geometrymatrix.go b/geometrymatrix.go
index d7449df16..a54d72c8b 100644
--- a/geometrymatrix.go
+++ b/geometrymatrix.go
@@ -22,6 +22,8 @@ import (
 const GeometryMatrixDim = 3
 
 // A GeometryMatrix represents a matrix to transform geometry when rendering an image.
+//
+// The initial value is identity.
 type GeometryMatrix struct {
 	// es represents elements.
 	es *[GeometryMatrixDim - 1][GeometryMatrixDim]float64
@@ -34,13 +36,6 @@ func geometryMatrixEsI() *[GeometryMatrixDim - 1][GeometryMatrixDim]float64 {
 	}
 }
 
-// NewGeometryMatrix returns an identity geometry matrix.
-func NewGeometryMatrix() GeometryMatrix {
-	return GeometryMatrix{
-		es: geometryMatrixEsI(),
-	}
-}
-
 func (g GeometryMatrix) dim() int {
 	return GeometryMatrixDim
 }