diff --git a/model/colorspace.go b/model/colorspace.go
index c40c9e72f..5b11e454b 100644
--- a/model/colorspace.go
+++ b/model/colorspace.go
@@ -1298,7 +1298,7 @@ func (cs *PdfColorspaceCalRGB) ImageToRGB(img Image) (Image, error) {
 	maxVal := math.Pow(2, float64(img.BitsPerComponent)) - 1
 
 	var rgbSamples []uint32
-	for i := 0; i < len(samples)-2; i++ {
+	for i := 0; i < len(samples)-2; i += 3 {
 		// A, B, C in range 0.0 to 1.0
 		aVal := float64(samples[i]) / maxVal
 		bVal := float64(samples[i+1]) / maxVal