mirror of https://github.com/SixLabors/ImageSharp
Brian Popow
6 years ago
6 changed files with 280 additions and 29 deletions
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// Copyright (c) Six Labors.
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// Licensed under the Apache License, Version 2.0.
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namespace SixLabors.ImageSharp.Formats.WebP.Lossy |
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{ |
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internal class Vp8CostArray |
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{ |
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/// <summary>
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/// Initializes a new instance of the <see cref="Vp8CostArray"/> class.
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/// </summary>
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public Vp8CostArray() |
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{ |
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this.Costs = new ushort[WebPConstants.NumCtx * (67 + 1)]; |
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} |
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public ushort[] Costs { get; } |
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} |
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} |
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// Copyright (c) Six Labors.
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// Licensed under the Apache License, Version 2.0.
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using System; |
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namespace SixLabors.ImageSharp.Formats.WebP.Lossy |
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{ |
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internal class Vp8EncProba |
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{ |
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/// <summary>
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/// Last (inclusive) level with variable cost.
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/// </summary>
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private const int MaxVariableLevel = 67; |
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/// <summary>
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/// Initializes a new instance of the <see cref="Vp8EncProba"/> class.
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/// </summary>
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public Vp8EncProba() |
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{ |
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this.Dirty = true; |
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this.UseSkipProba = false; |
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this.Segments = new byte[3]; |
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this.Coeffs = new Vp8BandProbas[WebPConstants.NumTypes][]; |
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for (int i = 0; i < this.Coeffs.Length; i++) |
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{ |
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this.Coeffs[i] = new Vp8BandProbas[WebPConstants.NumBands]; |
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for (int j = 0; j < this.Coeffs[i].Length; j++) |
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{ |
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this.Coeffs[i][j] = new Vp8BandProbas(); |
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} |
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} |
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this.LevelCost = new Vp8CostArray[WebPConstants.NumTypes][]; |
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for (int i = 0; i < this.LevelCost.Length; i++) |
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{ |
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this.LevelCost[i] = new Vp8CostArray[WebPConstants.NumBands]; |
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for (int j = 0; j < this.LevelCost[i].Length; j++) |
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{ |
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this.LevelCost[i][j] = new Vp8CostArray(); |
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} |
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} |
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this.RemappedCosts = new Vp8CostArray[WebPConstants.NumTypes][]; |
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for (int i = 0; i < this.RemappedCosts.Length; i++) |
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{ |
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this.RemappedCosts[i] = new Vp8CostArray[16]; |
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for (int j = 0; j < this.RemappedCosts[i].Length; j++) |
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{ |
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this.RemappedCosts[i][j] = new Vp8CostArray(); |
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} |
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} |
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// Initialize with default probabilities.
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this.Segments.AsSpan().Fill(255); |
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for (int t = 0; t < WebPConstants.NumTypes; ++t) |
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{ |
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for (int b = 0; b < WebPConstants.NumBands; ++b) |
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{ |
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for (int c = 0; c < WebPConstants.NumCtx; ++c) |
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{ |
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Vp8ProbaArray dst = this.Coeffs[t][b].Probabilities[c]; |
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for (int p = 0; p < WebPConstants.NumProbas; ++p) |
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{ |
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dst.Probabilities[p] = WebPLookupTables.DefaultCoeffsProba[t, b, c, p]; |
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} |
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} |
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} |
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} |
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} |
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/// <summary>
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/// Gets the probabilities for segment tree.
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/// </summary>
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public byte[] Segments { get; } |
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/// <summary>
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/// Gets the final probability of being skipped.
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/// </summary>
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public byte SkipProba { get; } |
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/// <summary>
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/// Gets a value indicating whether to use the skip probability. Note: we always use SkipProba for now.
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/// </summary>
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public bool UseSkipProba { get; } |
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public Vp8BandProbas[][] Coeffs { get; } |
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public Vp8CostArray[][] LevelCost { get; } |
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public Vp8CostArray[][] RemappedCosts { get; } |
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/// <summary>
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/// Gets or sets the number of skipped blocks.
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/// </summary>
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public int NbSkip { get; set; } |
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/// <summary>
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/// Gets or sets a value indicating whether CalculateLevelCosts() needs to be called.
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/// </summary>
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public bool Dirty { get; set; } |
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public void CalculateLevelCosts() |
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{ |
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if (!this.Dirty) |
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{ |
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return; // nothing to do.
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} |
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for (int ctype = 0; ctype < WebPConstants.NumTypes; ++ctype) |
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{ |
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for (int band = 0; band < WebPConstants.NumBands; ++band) |
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{ |
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for (int ctx = 0; ctx < WebPConstants.NumCtx; ++ctx) |
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{ |
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Vp8ProbaArray p = this.Coeffs[ctype][band].Probabilities[ctx]; |
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Span<ushort> table = this.LevelCost[ctype][band].Costs.AsSpan(ctx * MaxVariableLevel); |
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int cost0 = (ctx > 0) ? this.BitCost(1, p.Probabilities[0]) : 0; |
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int costBase = this.BitCost(1, p.Probabilities[1]) + cost0; |
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int v; |
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table[0] = (ushort)(this.BitCost(0, p.Probabilities[1]) + cost0); |
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for (v = 1; v <= MaxVariableLevel; ++v) |
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{ |
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table[v] = (ushort)(costBase + this.VariableLevelCost(v, p.Probabilities)); |
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} |
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// Starting at level 67 and up, the variable part of the cost is actually constant.
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} |
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} |
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for (int n = 0; n < 16; ++n) |
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{ |
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for (int ctx = 0; ctx < WebPConstants.NumCtx; ++ctx) |
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{ |
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Span<ushort> dst = this.RemappedCosts[ctype][n].Costs.AsSpan(ctx * MaxVariableLevel, MaxVariableLevel); |
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Span<ushort> src = this.LevelCost[ctype][WebPConstants.Bands[n]].Costs.AsSpan(ctx * MaxVariableLevel, MaxVariableLevel); |
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src.CopyTo(dst); |
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} |
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} |
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} |
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this.Dirty = false; |
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} |
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private int VariableLevelCost(int level, Span<byte> probas) |
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{ |
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int pattern = WebPLookupTables.Vp8LevelCodes[level - 1][0]; |
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int bits = WebPLookupTables.Vp8LevelCodes[level - 1][1]; |
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int cost = 0; |
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for (int i = 2; pattern != 0; ++i) |
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{ |
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if ((pattern & 1) != 0) |
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{ |
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cost += this.BitCost(bits & 1, probas[i]); |
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} |
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bits >>= 1; |
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pattern >>= 1; |
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} |
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return cost; |
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} |
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// Cost of coding one event with probability 'proba'.
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private int BitCost(int bit, byte proba) |
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{ |
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return bit == 0 ? WebPLookupTables.Vp8EntropyCost[proba] : WebPLookupTables.Vp8EntropyCost[255 - proba]; |
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} |
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} |
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} |
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