t.Errorf("%s, quality=%d: average delta is too high", tc.filename, tc.quality)
			continue
		}
	}
}

// TestWriteGrayscale tests that a grayscale images survives a round-trip
// through encode/decode cycle.
func TestWriteGrayscale(t *testing.T) {
	m0 := image.NewGray(image.Rect(0, 0, 32, 32))
	for i := range m0.Pix {
		m0.Pix[i] = uint8(i)
	}
	var buf bytes.Buffer