diff options
Diffstat (limited to 'libgo/go/image/jpeg/writer.go')
| -rw-r--r-- | libgo/go/image/jpeg/writer.go | 48 |
1 files changed, 27 insertions, 21 deletions
diff --git a/libgo/go/image/jpeg/writer.go b/libgo/go/image/jpeg/writer.go index 3322c09fe71..099298e462e 100644 --- a/libgo/go/image/jpeg/writer.go +++ b/libgo/go/image/jpeg/writer.go @@ -56,26 +56,28 @@ const ( nQuantIndex ) -// unscaledQuant are the unscaled quantization tables. Each encoder copies and -// scales the tables according to its quality parameter. +// unscaledQuant are the unscaled quantization tables in zig-zag order. Each +// encoder copies and scales the tables according to its quality parameter. +// The values are derived from section K.1 after converting from natural to +// zig-zag order. var unscaledQuant = [nQuantIndex][blockSize]byte{ // Luminance. { - 16, 11, 10, 16, 24, 40, 51, 61, - 12, 12, 14, 19, 26, 58, 60, 55, - 14, 13, 16, 24, 40, 57, 69, 56, - 14, 17, 22, 29, 51, 87, 80, 62, - 18, 22, 37, 56, 68, 109, 103, 77, - 24, 35, 55, 64, 81, 104, 113, 92, - 49, 64, 78, 87, 103, 121, 120, 101, - 72, 92, 95, 98, 112, 100, 103, 99, + 16, 11, 12, 14, 12, 10, 16, 14, + 13, 14, 18, 17, 16, 19, 24, 40, + 26, 24, 22, 22, 24, 49, 35, 37, + 29, 40, 58, 51, 61, 60, 57, 51, + 56, 55, 64, 72, 92, 78, 64, 68, + 87, 69, 55, 56, 80, 109, 81, 87, + 95, 98, 103, 104, 103, 62, 77, 113, + 121, 112, 100, 120, 92, 101, 103, 99, }, // Chrominance. { - 17, 18, 24, 47, 99, 99, 99, 99, - 18, 21, 26, 66, 99, 99, 99, 99, - 24, 26, 56, 99, 99, 99, 99, 99, - 47, 66, 99, 99, 99, 99, 99, 99, + 17, 18, 18, 24, 21, 24, 47, 26, + 26, 47, 99, 66, 56, 66, 99, 99, + 99, 99, 99, 99, 99, 99, 99, 99, + 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, 99, @@ -222,7 +224,7 @@ type encoder struct { buf [16]byte // bits and nBits are accumulated bits to write to w. bits, nBits uint32 - // quant is the scaled quantization tables. + // quant is the scaled quantization tables, in zig-zag order. quant [nQuantIndex][blockSize]byte } @@ -301,7 +303,7 @@ func (e *encoder) writeMarkerHeader(marker uint8, markerlen int) { // writeDQT writes the Define Quantization Table marker. func (e *encoder) writeDQT() { - markerlen := 2 + int(nQuantIndex)*(1+blockSize) + const markerlen = 2 + int(nQuantIndex)*(1+blockSize) e.writeMarkerHeader(dqtMarker, markerlen) for i := range e.quant { e.writeByte(uint8(i)) @@ -311,7 +313,7 @@ func (e *encoder) writeDQT() { // writeSOF0 writes the Start Of Frame (Baseline) marker. func (e *encoder) writeSOF0(size image.Point) { - markerlen := 8 + 3*nColorComponent + const markerlen = 8 + 3*nColorComponent e.writeMarkerHeader(sof0Marker, markerlen) e.buf[0] = 8 // 8-bit color. e.buf[1] = uint8(size.Y >> 8) @@ -344,6 +346,7 @@ func (e *encoder) writeDHT() { // writeBlock writes a block of pixel data using the given quantization table, // returning the post-quantized DC value of the DCT-transformed block. +// b is in natural (not zig-zag) order. func (e *encoder) writeBlock(b *block, q quantIndex, prevDC int) int { fdct(b) // Emit the DC delta. @@ -351,8 +354,8 @@ func (e *encoder) writeBlock(b *block, q quantIndex, prevDC int) int { e.emitHuffRLE(huffIndex(2*q+0), 0, dc-prevDC) // Emit the AC components. h, runLength := huffIndex(2*q+1), 0 - for k := 1; k < blockSize; k++ { - ac := div(b[unzig[k]], (8 * int(e.quant[q][k]))) + for zig := 1; zig < blockSize; zig++ { + ac := div(b[unzig[zig]], (8 * int(e.quant[q][zig]))) if ac == 0 { runLength++ } else { @@ -433,10 +436,12 @@ func scale(dst *block, src *[4]block) { // - component 1 uses DC table 0 and AC table 0 "\x01\x00", // - component 2 uses DC table 1 and AC table 1 "\x02\x11", // - component 3 uses DC table 1 and AC table 1 "\x03\x11", -// - padding "\x00\x00\x00". +// - the bytes "\x00\x3f\x00". Section B.2.3 of the spec says that for +// sequential DCTs, those bytes (8-bit Ss, 8-bit Se, 4-bit Ah, 4-bit Al) +// should be 0x00, 0x3f, 0x00<<4 | 0x00. var sosHeader = []byte{ 0xff, 0xda, 0x00, 0x0c, 0x03, 0x01, 0x00, 0x02, - 0x11, 0x03, 0x11, 0x00, 0x00, 0x00, + 0x11, 0x03, 0x11, 0x00, 0x3f, 0x00, } // writeSOS writes the StartOfScan marker. @@ -444,6 +449,7 @@ func (e *encoder) writeSOS(m image.Image) { e.write(sosHeader) var ( // Scratch buffers to hold the YCbCr values. + // The blocks are in natural (not zig-zag) order. yBlock block cbBlock [4]block crBlock [4]block |