quant.go (3114B)
1 // Copyright 2011 The Go Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style 3 // license that can be found in the LICENSE file. 4 5 package vp8 6 7 // This file implements parsing the quantization factors. 8 9 // quant are DC/AC quantization factors. 10 type quant struct { 11 y1 [2]uint16 12 y2 [2]uint16 13 uv [2]uint16 14 } 15 16 // clip clips x to the range [min, max] inclusive. 17 func clip(x, min, max int32) int32 { 18 if x < min { 19 return min 20 } 21 if x > max { 22 return max 23 } 24 return x 25 } 26 27 // parseQuant parses the quantization factors, as specified in section 9.6. 28 func (d *Decoder) parseQuant() { 29 baseQ0 := d.fp.readUint(uniformProb, 7) 30 dqy1DC := d.fp.readOptionalInt(uniformProb, 4) 31 const dqy1AC = 0 32 dqy2DC := d.fp.readOptionalInt(uniformProb, 4) 33 dqy2AC := d.fp.readOptionalInt(uniformProb, 4) 34 dquvDC := d.fp.readOptionalInt(uniformProb, 4) 35 dquvAC := d.fp.readOptionalInt(uniformProb, 4) 36 for i := 0; i < nSegment; i++ { 37 q := int32(baseQ0) 38 if d.segmentHeader.useSegment { 39 if d.segmentHeader.relativeDelta { 40 q += int32(d.segmentHeader.quantizer[i]) 41 } else { 42 q = int32(d.segmentHeader.quantizer[i]) 43 } 44 } 45 d.quant[i].y1[0] = dequantTableDC[clip(q+dqy1DC, 0, 127)] 46 d.quant[i].y1[1] = dequantTableAC[clip(q+dqy1AC, 0, 127)] 47 d.quant[i].y2[0] = dequantTableDC[clip(q+dqy2DC, 0, 127)] * 2 48 d.quant[i].y2[1] = dequantTableAC[clip(q+dqy2AC, 0, 127)] * 155 / 100 49 if d.quant[i].y2[1] < 8 { 50 d.quant[i].y2[1] = 8 51 } 52 // The 117 is not a typo. The dequant_init function in the spec's Reference 53 // Decoder Source Code (http://tools.ietf.org/html/rfc6386#section-9.6 Page 145) 54 // says to clamp the LHS value at 132, which is equal to dequantTableDC[117]. 55 d.quant[i].uv[0] = dequantTableDC[clip(q+dquvDC, 0, 117)] 56 d.quant[i].uv[1] = dequantTableAC[clip(q+dquvAC, 0, 127)] 57 } 58 } 59 60 // The dequantization tables are specified in section 14.1. 61 var ( 62 dequantTableDC = [128]uint16{ 63 4, 5, 6, 7, 8, 9, 10, 10, 64 11, 12, 13, 14, 15, 16, 17, 17, 65 18, 19, 20, 20, 21, 21, 22, 22, 66 23, 23, 24, 25, 25, 26, 27, 28, 67 29, 30, 31, 32, 33, 34, 35, 36, 68 37, 37, 38, 39, 40, 41, 42, 43, 69 44, 45, 46, 46, 47, 48, 49, 50, 70 51, 52, 53, 54, 55, 56, 57, 58, 71 59, 60, 61, 62, 63, 64, 65, 66, 72 67, 68, 69, 70, 71, 72, 73, 74, 73 75, 76, 76, 77, 78, 79, 80, 81, 74 82, 83, 84, 85, 86, 87, 88, 89, 75 91, 93, 95, 96, 98, 100, 101, 102, 76 104, 106, 108, 110, 112, 114, 116, 118, 77 122, 124, 126, 128, 130, 132, 134, 136, 78 138, 140, 143, 145, 148, 151, 154, 157, 79 } 80 dequantTableAC = [128]uint16{ 81 4, 5, 6, 7, 8, 9, 10, 11, 82 12, 13, 14, 15, 16, 17, 18, 19, 83 20, 21, 22, 23, 24, 25, 26, 27, 84 28, 29, 30, 31, 32, 33, 34, 35, 85 36, 37, 38, 39, 40, 41, 42, 43, 86 44, 45, 46, 47, 48, 49, 50, 51, 87 52, 53, 54, 55, 56, 57, 58, 60, 88 62, 64, 66, 68, 70, 72, 74, 76, 89 78, 80, 82, 84, 86, 88, 90, 92, 90 94, 96, 98, 100, 102, 104, 106, 108, 91 110, 112, 114, 116, 119, 122, 125, 128, 92 131, 134, 137, 140, 143, 146, 149, 152, 93 155, 158, 161, 164, 167, 170, 173, 177, 94 181, 185, 189, 193, 197, 201, 205, 209, 95 213, 217, 221, 225, 229, 234, 239, 245, 96 249, 254, 259, 264, 269, 274, 279, 284, 97 } 98 )