image/png: remove unnecessary function call

paeth(0, x, 0) == x for any uint8 value.

LGTM=nigeltao
R=golang-codereviews, bradfitz, nigeltao
CC=golang-codereviews
https://golang.org/cl/105290049

diff --git a/src/pkg/image/png/writer.go b/src/pkg/image/png/writer.go
index 629452cbfa1b88a0c47331f1b6e057ee370c894b..5c232b760a50ca014512312b7f27fd592c797972 100644 (file)
--- a/src/pkg/image/png/writer.go
+++ b/src/pkg/image/png/writer.go
@@ -188,7 +188,7 @@ func filter(cr *[nFilter][]byte, pr []byte, bpp int) int {
        // The Paeth filter.
        sum = 0
        for i := 0; i < bpp; i++ {
-               cdat4[i] = cdat0[i] - paeth(0, pdat[i], 0)
+               cdat4[i] = cdat0[i] - pdat[i]
                sum += abs8(cdat4[i])
        }
        for i := bpp; i < n; i++ {