tsai
/
ImageSharp
mirror of https://github.com/SixLabors/ImageSharp
1
0
Fork 0
Code Issues Projects Releases Wiki Activity
Browse Source

Paragraph 9.6: Dequantization Indices

pull/1552/head
Brian Popow 6 years ago
parent
2acb3df0ea
commit
795617bdcf
3 changed files with 114 additions and 6 deletions
Whitespace
Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL
Split View
Diff Options
Show Stats Download Patch File Download Diff File
  1. 4
      src/ImageSharp/Formats/WebP/AlphaDecoder.cs
  2. 48
      src/ImageSharp/Formats/WebP/WebPConstants.cs
  3. 68
      src/ImageSharp/Formats/WebP/WebPDecoderCore.cs

4
src/ImageSharp/Formats/WebP/AlphaDecoder.cs
View File

@ -1,8 +1,10 @@
// Copyright (c) Six Labors and contributors.
// Copyright (c) Six Labors and contributors.
// Licensed under the Apache License, Version 2.0.
using System;
using SixLabors.ImageSharp.Formats.WebP.Filters;
namespace SixLabors.ImageSharp.Formats.WebP
{
internal ref struct AlphaDecoder

48
src/ImageSharp/Formats/WebP/WebPConstants.cs
View File

@ -70,7 +70,7 @@ namespace SixLabors.ImageSharp.Formats.WebP
public const int MaxColorCacheBits = 11;
/// <summary>
/// The maximum number of allowed transforms in a bitstream.
/// The maximum number of allowed transforms in a VP8L bitstream.
/// </summary>
public const int MaxNumberOfTransforms = 4;
@ -104,5 +104,51 @@ namespace SixLabors.ImageSharp.Formats.WebP
NumLiteralCodes, NumLiteralCodes, NumLiteralCodes,
NumDistanceCodes
};
// VP8 constants
public const int NumMbSegments = 4;
public const int MaxNumPartitions = 8;
// Paragraph 14.1
public static readonly int[] DcTable =
{
4, 5, 6, 7, 8, 9, 10, 10,
11, 12, 13, 14, 15, 16, 17, 17,
18, 19, 20, 20, 21, 21, 22, 22,
23, 23, 24, 25, 25, 26, 27, 28,
29, 30, 31, 32, 33, 34, 35, 36,
37, 37, 38, 39, 40, 41, 42, 43,
44, 45, 46, 46, 47, 48, 49, 50,
51, 52, 53, 54, 55, 56, 57, 58,
59, 60, 61, 62, 63, 64, 65, 66,
67, 68, 69, 70, 71, 72, 73, 74,
75, 76, 76, 77, 78, 79, 80, 81,
82, 83, 84, 85, 86, 87, 88, 89,
91, 93, 95, 96, 98, 100, 101, 102,
104, 106, 108, 110, 112, 114, 116, 118,
122, 124, 126, 128, 130, 132, 134, 136,
138, 140, 143, 145, 148, 151, 154, 157
};
public static readonly int[] AcTable =
{
4, 5, 6, 7, 8, 9, 10, 11,
12, 13, 14, 15, 16, 17, 18, 19,
20, 21, 22, 23, 24, 25, 26, 27,
28, 29, 30, 31, 32, 33, 34, 35,
36, 37, 38, 39, 40, 41, 42, 43,
44, 45, 46, 47, 48, 49, 50, 51,
52, 53, 54, 55, 56, 57, 58, 60,
62, 64, 66, 68, 70, 72, 74, 76,
78, 80, 82, 84, 86, 88, 90, 92,
94, 96, 98, 100, 102, 104, 106, 108,
110, 112, 114, 116, 119, 122, 125, 128,
131, 134, 137, 140, 143, 146, 149, 152,
155, 158, 161, 164, 167, 170, 173, 177,
181, 185, 189, 193, 197, 201, 205, 209,
213, 217, 221, 225, 229, 234, 239, 245,
249, 254, 259, 264, 269, 274, 279, 284
};
}
}

68
src/ImageSharp/Formats/WebP/WebPDecoderCore.cs
View File

@ -374,6 +374,7 @@ namespace SixLabors.ImageSharp.Formats.WebP
// Paragraph 9.3: Parse the segment header.
var vp8SegmentHeader = new Vp8SegmentHeader();
vp8SegmentHeader.UseSegment = bitReader.ReadBool();
bool hasValue = false;
if (vp8SegmentHeader.UseSegment)
{
vp8SegmentHeader.UpdateMap = bitReader.ReadBool();
@ -383,14 +384,14 @@ namespace SixLabors.ImageSharp.Formats.WebP
vp8SegmentHeader.Delta = bitReader.ReadBool();
for (int i = 0; i < vp8SegmentHeader.Quantizer.Length; i++)
{
bool hasValue = bitReader.ReadBool();
hasValue = bitReader.ReadBool();
uint quantizeValue = hasValue ? bitReader.ReadValue(7) : 0;
vp8SegmentHeader.Quantizer[i] = (byte)quantizeValue;
}
for (int i = 0; i < vp8SegmentHeader.FilterStrength.Length; i++)
{
bool hasValue = bitReader.ReadBool();
hasValue = bitReader.ReadBool();
uint filterStrengthValue = hasValue ? bitReader.ReadValue(6) : 0;
vp8SegmentHeader.FilterStrength[i] = (byte)filterStrengthValue;
}
@ -419,7 +420,7 @@ namespace SixLabors.ImageSharp.Formats.WebP
{
for (int i = 0; i < vp8FilterHeader.RefLfDelta.Length; i++)
{
bool hasValue = bitReader.ReadBool();
hasValue = bitReader.ReadBool();
if (hasValue)
{
vp8FilterHeader.RefLfDelta[i] = bitReader.ReadSignedValue(6);
@ -428,7 +429,7 @@ namespace SixLabors.ImageSharp.Formats.WebP
for (int i = 0; i < vp8FilterHeader.ModeLfDelta.Length; i++)
{
bool hasValue = bitReader.ReadBool();
hasValue = bitReader.ReadBool();
if (hasValue)
{
vp8FilterHeader.ModeLfDelta[i] = bitReader.ReadSignedValue(6);
@ -442,7 +443,61 @@ namespace SixLabors.ImageSharp.Formats.WebP
int lastPart = numPartsMinusOne;
// TODO: check if we have enough data available here, throw exception if not
// Paragraph 9.6: Dequantization Indices
int baseQ0 = (int)bitReader.ReadValue(7);
hasValue = bitReader.ReadBool();
int dqy1Dc = hasValue ? bitReader.ReadSignedValue(4) : 0;
hasValue = bitReader.ReadBool();
int dqy2Dc = hasValue ? bitReader.ReadSignedValue(4) : 0;
hasValue = bitReader.ReadBool();
int dqy2Ac = hasValue ? bitReader.ReadSignedValue(4) : 0;
hasValue = bitReader.ReadBool();
int dquvDc = hasValue ? bitReader.ReadSignedValue(4) : 0;
hasValue = bitReader.ReadBool();
int dquvAc = hasValue ? bitReader.ReadSignedValue(4) : 0;
for (int i = 0; i < WebPConstants.NumMbSegments; ++i)
{
int q;
if (vp8SegmentHeader.UseSegment)
{
q = vp8SegmentHeader.Quantizer[i];
if (!vp8SegmentHeader.Delta)
{
q += baseQ0;
}
}
else
{
if (i > 0)
{
// dec->dqm_[i] = dec->dqm_[0];
continue;
}
else
{
q = baseQ0;
}
}
var m = new Vp8QuantMatrix();
m.Y1Mat[0] = WebPConstants.DcTable[this.Clip(q + dqy1Dc, 127)];
m.Y1Mat[1] = WebPConstants.AcTable[this.Clip(q + 0, 127)];
m.Y2Mat[0] = WebPConstants.DcTable[this.Clip(q + dqy2Dc, 127)] * 2;
// For all x in [0..284], x*155/100 is bitwise equal to (x*101581) >> 16.
// The smallest precision for that is '(x*6349) >> 12' but 16 is a good word size.
m.Y2Mat[1] = (WebPConstants.AcTable[this.Clip(q + dqy2Ac, 127)] * 101581) >> 16;
if (m.Y2Mat[1] < 8)
{
m.Y2Mat[1] = 8;
}
m.UVMat[0] = WebPConstants.DcTable[this.Clip(q + dquvDc, 117)];
m.UVMat[1] = WebPConstants.AcTable[this.Clip(q + dquvAc, 127)];
// For dithering strength evaluation.
m.UvQuant = q + dquvAc;
}
return new WebPImageInfo()
{
@ -578,5 +633,10 @@ namespace SixLabors.ImageSharp.Formats.WebP
throw new ImageFormatException("Invalid WebP data.");
}
private int Clip(int v, int M)
{
return v < 0 ? 0 : v > M ? M : v;
}
}
}

Write Preview
Loading…
Cancel
Save