go.image/tiff: encoder fix non LZW Predictor and Paletted SamplesPerPixel and non RGB ExtraSamples.
TIFF6.0 Spec:
Page 31: ExtraSamples can only included in RGB mode image.
Page 39, SamplesPerPixel is usually 1 for bilevel, grayscale, and palette-color images.
Page 64, Currently Predictor field is used only with LZW.
Fixes golang/go#6421.
R=bsiegert, nigeltao, gbulmer
CC=golang-dev
https://golang.org/cl/13779043
diff --git a/tiff/writer.go b/tiff/writer.go
index 531dbc4..c8a01ce 100644
--- a/tiff/writer.go
+++ b/tiff/writer.go
@@ -291,11 +291,12 @@
func Encode(w io.Writer, m image.Image, opt *Options) error {
d := m.Bounds().Size()
- predictor := false
compression := uint32(cNone)
+ predictor := false
if opt != nil {
- predictor = opt.Predictor
compression = opt.Compression.specValue()
+ // The predictor field is only used with LZW. See page 64 of the spec.
+ predictor = opt.Predictor && compression == cLZW
}
_, err := io.WriteString(w, leHeader)
@@ -343,7 +344,7 @@
photometricInterpretation := uint32(pRGB)
samplesPerPixel := uint32(4)
bitsPerSample := []uint32{8, 8, 8, 8}
- extrasamples := uint32(1) // Associated alpha (default).
+ extraSamples := uint32(0)
colorMap := []uint32{}
if predictor {
@@ -352,7 +353,7 @@
switch m := m.(type) {
case *image.Paletted:
photometricInterpretation = pPaletted
- samplesPerPixel = 3
+ samplesPerPixel = 1
bitsPerSample = []uint32{8}
colorMap = make([]uint32, 256*3)
for i := 0; i < 256 && i < len(m.Palette); i++ {
@@ -373,18 +374,21 @@
bitsPerSample = []uint32{16}
err = encodeGray16(dst, m.Pix, d.X, d.Y, m.Stride, predictor)
case *image.NRGBA:
- extrasamples = 2 // Unassociated alpha.
+ extraSamples = 2 // Unassociated alpha.
err = encodeRGBA(dst, m.Pix, d.X, d.Y, m.Stride, predictor)
case *image.NRGBA64:
- extrasamples = 2 // Unassociated alpha.
+ extraSamples = 2 // Unassociated alpha.
bitsPerSample = []uint32{16, 16, 16, 16}
err = encodeRGBA64(dst, m.Pix, d.X, d.Y, m.Stride, predictor)
case *image.RGBA:
+ extraSamples = 1 // Associated alpha.
err = encodeRGBA(dst, m.Pix, d.X, d.Y, m.Stride, predictor)
case *image.RGBA64:
+ extraSamples = 1 // Associated alpha.
bitsPerSample = []uint32{16, 16, 16, 16}
err = encodeRGBA64(dst, m.Pix, d.X, d.Y, m.Stride, predictor)
default:
+ extraSamples = 1 // Associated alpha.
err = encode(dst, m, predictor)
}
if err != nil {
@@ -419,12 +423,16 @@
{tXResolution, dtRational, []uint32{72, 1}},
{tYResolution, dtRational, []uint32{72, 1}},
{tResolutionUnit, dtShort, []uint32{resPerInch}},
- {tPredictor, dtShort, []uint32{pr}},
- {tExtraSamples, dtShort, []uint32{extrasamples}},
+ }
+ if pr != prNone {
+ ifd = append(ifd, ifdEntry{tPredictor, dtShort, []uint32{pr}})
}
if len(colorMap) != 0 {
ifd = append(ifd, ifdEntry{tColorMap, dtShort, colorMap})
}
+ if extraSamples > 0 {
+ ifd = append(ifd, ifdEntry{tExtraSamples, dtShort, []uint32{extraSamples}})
+ }
return writeIFD(w, imageLen+8, ifd)
}
