diff --git a/mnist.go b/mnist.go
index 5418363..37b6bf3 100644
--- a/mnist.go
+++ b/mnist.go
@@ -49,6 +49,11 @@ func (img RawImage) At(x, y int) color.Color {
 	return color.Gray{img[y*Width+x]}
 }
 
+func (img RawImage) AtGray(x, y int) color.Gray {
+    return color.Gray{img[y*Width+x]}
+}
+
+
 // ReadImageFile opens the named image file (training or test), parses it and
 // returns all images in order.
 func ReadImageFile(name string) (rows, cols int, imgs []RawImage, err error) {
diff --git a/util.go b/util.go
index 1a015ed..95b77f6 100644
--- a/util.go
+++ b/util.go
@@ -57,6 +57,7 @@ type Sweeper struct {
 // Next returns the next image and its label in the data set.
 // If the end is reached, present is set to false.
 func (sw *Sweeper) Next() (image RawImage, label Label, present bool) {
+	sw.i++
 	if sw.i >= len(sw.set.Images) {
 		return nil, 0, false
 	}
@@ -65,7 +66,7 @@ func (sw *Sweeper) Next() (image RawImage, label Label, present bool) {
 
 // Sweep creates a new sweep iterator over the data set
 func (s *Set) Sweep() *Sweeper {
-	return &Sweeper{set: s}
+	return &Sweeper{set: s, i: -1}
 }
 
 // Load reads both the training and the testing MNIST data sets, given