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JpegScanDecoder docs

pull/62/head
Anton Firszov 10 years ago
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2 changed files with 166 additions and 135 deletions
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  1. 293
      src/ImageSharp/Formats/Jpg/Components/Decoder/JpegScanDecoder.cs
  2. 8
      src/ImageSharp/Formats/Jpg/Components/Decoder/JpegScanDecoder.md

293
src/ImageSharp/Formats/Jpg/Components/Decoder/JpegScanDecoder.cs
View File

@ -25,7 +25,7 @@ namespace ImageSharp.Formats.Jpg
/// Holds the "large" data blocks needed for computations /// Holds the "large" data blocks needed for computations
/// </summary> /// </summary>
[StructLayout(LayoutKind.Sequential)] [StructLayout(LayoutKind.Sequential)]
public struct ComponentData public struct ComputationData
{ {
/// <summary> /// <summary>
/// The main input block /// The main input block
@ -58,42 +58,63 @@ namespace ImageSharp.Formats.Jpg
public fixed byte ScanData[3 * JpegDecoderCore.MaxComponents]; public fixed byte ScanData[3 * JpegDecoderCore.MaxComponents];
/// <summary> /// <summary>
/// The DC data /// The DC component values
/// </summary> /// </summary>
public fixed int Dc[JpegDecoderCore.MaxComponents]; public fixed int Dc[JpegDecoderCore.MaxComponents];
/// <summary> /// <summary>
/// Creates and initializes a new <see cref="ComponentData"/> instance /// Creates and initializes a new <see cref="ComputationData"/> instance
/// </summary> /// </summary>
/// <returns></returns> /// <returns></returns>
public static ComponentData Create() public static ComputationData Create()
{ {
ComponentData data = default(ComponentData); ComputationData data = default(ComputationData);
data.Unzig = UnzigData.Create(); data.Unzig = UnzigData.Create();
return data; return data;
} }
} }
/// <summary> /// <summary>
/// Contains pointers to the memory regions of <see cref="ComponentData"/> so they can be easily passed around to pointer based utility methods of <see cref="Block8x8F"/> /// Contains pointers to the memory regions of <see cref="ComputationData"/> so they can be easily passed around to pointer based utility methods of <see cref="Block8x8F"/>
/// </summary> /// </summary>
public struct ComponentPointers public struct DataPointers
{ {
/// <summary>
/// Pointer to <see cref="ComputationData.Block"/>
/// </summary>
public Block8x8F* Block; public Block8x8F* Block;
/// <summary>
/// Pointer to <see cref="ComputationData.Temp1"/>
/// </summary>
public Block8x8F* Temp1; public Block8x8F* Temp1;
/// <summary>
/// Pointer to <see cref="ComputationData.Temp2"/>
/// </summary>
public Block8x8F* Temp2; public Block8x8F* Temp2;
/// <summary>
/// Pointer to <see cref="ComputationData.QuantiazationTable"/>
/// </summary>
public Block8x8F* QuantiazationTable; public Block8x8F* QuantiazationTable;
/// <summary>
/// Pointer to <see cref="ComputationData.Unzig"/> as int*
/// </summary>
public int* Unzig; public int* Unzig;
/// <summary>
/// Pointer to <see cref="ComputationData.ScanData"/> as Scan*
/// </summary>
public Scan* Scan; public Scan* Scan;
/// <summary>
/// Pointer to <see cref="ComputationData.Dc"/>
/// </summary>
public int* Dc; public int* Dc;
public ComponentPointers(ComponentData* basePtr) public DataPointers(ComputationData* basePtr)
{ {
this.Block = &basePtr->Block; this.Block = &basePtr->Block;
this.Temp1 = &basePtr->Temp1; this.Temp1 = &basePtr->Temp1;
@ -171,35 +192,38 @@ namespace ImageSharp.Formats.Jpg
/// </summary> /// </summary>
public int YNumberOfMCUs; public int YNumberOfMCUs;
private int scanComponentCount; /// <summary>
/// The number of component scans
/// </summary>
private int componentScanCount;
/// <summary> /// <summary>
/// The <see cref="ComponentData"/> buffer /// The <see cref="ComputationData"/> buffer
/// </summary> /// </summary>
private ComponentData Data; private ComputationData Data;
/// <summary> /// <summary>
/// Pointers to elements of <see cref="Data"/> /// Pointers to elements of <see cref="Data"/>
/// </summary> /// </summary>
private ComponentPointers Pointers; private DataPointers Pointers;
/// <summary> /// <summary>
/// Initializes the default instance after creation /// Initializes the default instance after creation.
/// </summary> /// </summary>
/// <param name="p"></param> /// <param name="p">Pointer to <see cref="JpegScanDecoder"/> on the stack</param>
/// <param name="decoder"></param> /// <param name="decoder">The <see cref="JpegDecoderCore"/> instance</param>
/// <param name="remaining"></param> /// <param name="remaining">The remaining bytes in the segment block.</param>
public static void Init(JpegScanDecoder* p, JpegDecoderCore decoder, int remaining) public static void Init(JpegScanDecoder* p, JpegDecoderCore decoder, int remaining)
{ {
p->Data = ComponentData.Create(); p->Data = ComputationData.Create();
p->Pointers = new ComponentPointers(&p->Data); p->Pointers = new DataPointers(&p->Data);
p->InitImpl(decoder, remaining); p->InitImpl(decoder, remaining);
} }
/// <summary> /// <summary>
/// Reads the blocks from the <see cref="JpegDecoderCore"/>-s stream, and processes them into the corresponding <see cref="JpegPixelArea"/> instances. /// Reads the blocks from the <see cref="JpegDecoderCore"/>-s stream, and processes them into the corresponding <see cref="JpegPixelArea"/> instances.
/// </summary> /// </summary>
/// <param name="decoder"></param> /// <param name="decoder">The <see cref="JpegDecoderCore"/> instance</param>
public void ProcessBlocks(JpegDecoderCore decoder) public void ProcessBlocks(JpegDecoderCore decoder)
{ {
int blockCount = 0; int blockCount = 0;
@ -210,7 +234,7 @@ namespace ImageSharp.Formats.Jpg
{ {
for (int mx = 0; mx < this.XNumberOfMCUs; mx++) for (int mx = 0; mx < this.XNumberOfMCUs; mx++)
{ {
for (int i = 0; i < this.scanComponentCount; i++) for (int i = 0; i < this.componentScanCount; i++)
{ {
int compIndex = this.Pointers.Scan[i].Index; int compIndex = this.Pointers.Scan[i].Index;
int hi = decoder.ComponentArray[compIndex].HorizontalFactor; int hi = decoder.ComponentArray[compIndex].HorizontalFactor;
@ -240,7 +264,7 @@ namespace ImageSharp.Formats.Jpg
// The non-interleaved scans will process only 6 Y blocks: // The non-interleaved scans will process only 6 Y blocks:
// 0 1 2 // 0 1 2
// 3 4 5 // 3 4 5
if (this.scanComponentCount != 1) if (this.componentScanCount != 1)
{ {
this.bx = (hi * mx) + (j % hi); this.bx = (hi * mx) + (j % hi);
this.by = (vi * my) + (j / hi); this.by = (vi * my) + (j / hi);
@ -332,9 +356,9 @@ namespace ImageSharp.Formats.Jpg
} }
decoder.ReadFull(decoder.Temp, 0, remaining); decoder.ReadFull(decoder.Temp, 0, remaining);
this.scanComponentCount = decoder.Temp[0]; this.componentScanCount = decoder.Temp[0];
int scanComponentCountX2 = 2 * this.scanComponentCount; int scanComponentCountX2 = 2 * this.componentScanCount;
if (remaining != 4 + scanComponentCountX2) if (remaining != 4 + scanComponentCountX2)
{ {
throw new ImageFormatException("SOS length inconsistent with number of components"); throw new ImageFormatException("SOS length inconsistent with number of components");
@ -342,10 +366,11 @@ namespace ImageSharp.Formats.Jpg
int totalHv = 0; int totalHv = 0;
for (int i = 0; i < this.scanComponentCount; i++) for (int i = 0; i < this.componentScanCount; i++)
{ {
this.ProcessScanImpl(decoder, i, ref this.Pointers.Scan[i], ref totalHv); this.ProcessScanImpl(decoder, i, ref this.Pointers.Scan[i], ref totalHv);
} }
// Section B.2.3 states that if there is more than one component then the // Section B.2.3 states that if there is more than one component then the
// total H*V values in a scan must be <= 10. // total H*V values in a scan must be <= 10.
if (decoder.ComponentCount > 1 && totalHv > 10) if (decoder.ComponentCount > 1 && totalHv > 10)
@ -368,7 +393,7 @@ namespace ImageSharp.Formats.Jpg
throw new ImageFormatException("Bad spectral selection bounds"); throw new ImageFormatException("Bad spectral selection bounds");
} }
if (this.zigStart != 0 && this.scanComponentCount != 1) if (this.zigStart != 0 && this.componentScanCount != 1)
{ {
throw new ImageFormatException("Progressive AC coefficients for more than one component"); throw new ImageFormatException("Progressive AC coefficients for more than one component");
} }
@ -387,7 +412,7 @@ namespace ImageSharp.Formats.Jpg
if (decoder.IsProgressive) if (decoder.IsProgressive)
{ {
for (int i = 0; i < this.scanComponentCount; i++) for (int i = 0; i < this.componentScanCount; i++)
{ {
int compIndex = this.Pointers.Scan[i].Index; int compIndex = this.Pointers.Scan[i].Index;
if (decoder.ProgCoeffs[compIndex] == null) if (decoder.ProgCoeffs[compIndex] == null)
@ -401,6 +426,117 @@ namespace ImageSharp.Formats.Jpg
} }
} }
/// <summary>
/// Process the current block at (<see cref="bx"/>, <see cref="by"/>)
/// </summary>
/// <param name="decoder">The decoder</param>
/// <param name="i">The index of the scan</param>
/// <param name="compIndex">The component index</param>
/// <param name="hi">Horizontal sampling factor at the given component index</param>
private void ProcessBlockImpl(JpegDecoderCore decoder, int i, int compIndex, int hi)
{
var b = this.Pointers.Block;
//var dc = this.Pointers.Dc;
int huffmannIdx = (AcTableIndex * HuffmanTree.ThRowSize) + this.Pointers.Scan[i].AcTableSelector;
if (this.ah != 0)
{
this.Refine(decoder, ref decoder.HuffmanTrees[huffmannIdx], 1 << this.al);
}
else
{
int zig = this.zigStart;
if (zig == 0)
{
zig++;
// Decode the DC coefficient, as specified in section F.2.2.1.
byte value =
decoder.DecodeHuffman(
ref decoder.HuffmanTrees[(DcTableIndex * HuffmanTree.ThRowSize) + this.Pointers.Scan[i].DcTableSelector]);
if (value > 16)
{
throw new ImageFormatException("Excessive DC component");
}
int deltaDC = decoder.Bits.ReceiveExtend(value, decoder);
this.Pointers.Dc[compIndex] += deltaDC;
// b[0] = dc[compIndex] << al;
Block8x8F.SetScalarAt(b, 0, this.Pointers.Dc[compIndex] << al);
}
if (zig <= this.zigEnd && decoder.EobRun > 0)
{
decoder.EobRun--;
}
else
{
// Decode the AC coefficients, as specified in section F.2.2.2.
for (; zig <= this.zigEnd; zig++)
{
byte value = decoder.DecodeHuffman(ref decoder.HuffmanTrees[huffmannIdx]);
byte val0 = (byte)(value >> 4);
byte val1 = (byte)(value & 0x0f);
if (val1 != 0)
{
zig += val0;
if (zig > this.zigEnd)
{
break;
}
int ac = decoder.Bits.ReceiveExtend(val1, decoder);
// b[Unzig[zig]] = ac << al;
Block8x8F.SetScalarAt(b, this.Pointers.Unzig[zig], ac << this.al);
}
else
{
if (val0 != 0x0f)
{
decoder.EobRun = (ushort)(1 << val0);
if (val0 != 0)
{
decoder.EobRun |= (ushort)decoder.DecodeBits(val0);
}
decoder.EobRun--;
break;
}
zig += 0x0f;
}
}
}
}
if (decoder.IsProgressive)
{
if (this.zigEnd != Block8x8F.ScalarCount - 1 || this.al != 0)
{
// We haven't completely decoded this 8x8 block. Save the coefficients.
// this.ProgCoeffs[compIndex][((@by * XNumberOfMCUs) * hi) + bx] = b.Clone();
decoder.ProgCoeffs[compIndex][((this.by * this.XNumberOfMCUs) * hi) + this.bx] = *b;
// At this point, we could execute the rest of the loop body to dequantize and
// perform the inverse DCT, to save early stages of a progressive image to the
// *image.YCbCr buffers (the whole point of progressive encoding), but in Go,
// the jpeg.Decode function does not return until the entire image is decoded,
// so we "continue" here to avoid wasted computation.
return;
}
}
// Dequantize, perform the inverse DCT and store the block to the image.
Block8x8F.UnZig(b, this.Pointers.QuantiazationTable, this.Pointers.Unzig);
DCT.TransformIDCT(ref *b, ref *this.Pointers.Temp1, ref *this.Pointers.Temp2);
var destChannel = decoder.GetDestinationChannel(compIndex);
var destArea = destChannel.GetOffsetedSubAreaForBlock(this.bx, this.by);
destArea.LoadColorsFrom(this.Pointers.Temp1, this.Pointers.Temp2);
}
private void ProcessScanImpl(JpegDecoderCore decoder, int i, ref Scan currentScan, ref int totalHv) private void ProcessScanImpl(JpegDecoderCore decoder, int i, ref Scan currentScan, ref int totalHv)
{ {
// Component selector. // Component selector.
@ -608,110 +744,5 @@ namespace ImageSharp.Formats.Jpg
return zig; return zig;
} }
private void ProcessBlockImpl(JpegDecoderCore decoder, int i, int compIndex, int hi)
{
var b = this.Pointers.Block;
//var dc = this.Pointers.Dc;
int huffmannIdx = (AcTableIndex * HuffmanTree.ThRowSize) + this.Pointers.Scan[i].AcTableSelector;
if (this.ah != 0)
{
this.Refine(decoder, ref decoder.HuffmanTrees[huffmannIdx], 1 << this.al);
}
else
{
int zig = this.zigStart;
if (zig == 0)
{
zig++;
// Decode the DC coefficient, as specified in section F.2.2.1.
byte value =
decoder.DecodeHuffman(
ref decoder.HuffmanTrees[(DcTableIndex * HuffmanTree.ThRowSize) + this.Pointers.Scan[i].DcTableSelector]);
if (value > 16)
{
throw new ImageFormatException("Excessive DC component");
}
int deltaDC = decoder.Bits.ReceiveExtend(value, decoder);
this.Pointers.Dc[compIndex] += deltaDC;
// b[0] = dc[compIndex] << al;
Block8x8F.SetScalarAt(b, 0, this.Pointers.Dc[compIndex] << al);
}
if (zig <= this.zigEnd && decoder.EobRun > 0)
{
decoder.EobRun--;
}
else
{
// Decode the AC coefficients, as specified in section F.2.2.2.
for (; zig <= this.zigEnd; zig++)
{
byte value = decoder.DecodeHuffman(ref decoder.HuffmanTrees[huffmannIdx]);
byte val0 = (byte)(value >> 4);
byte val1 = (byte)(value & 0x0f);
if (val1 != 0)
{
zig += val0;
if (zig > this.zigEnd)
{
break;
}
int ac = decoder.Bits.ReceiveExtend(val1, decoder);
// b[Unzig[zig]] = ac << al;
Block8x8F.SetScalarAt(b, this.Pointers.Unzig[zig], ac << this.al);
}
else
{
if (val0 != 0x0f)
{
decoder.EobRun = (ushort)(1 << val0);
if (val0 != 0)
{
decoder.EobRun |= (ushort)decoder.DecodeBits(val0);
}
decoder.EobRun--;
break;
}
zig += 0x0f;
}
}
}
}
if (decoder.IsProgressive)
{
if (this.zigEnd != Block8x8F.ScalarCount - 1 || this.al != 0)
{
// We haven't completely decoded this 8x8 block. Save the coefficients.
// this.ProgCoeffs[compIndex][((@by * XNumberOfMCUs) * hi) + bx] = b.Clone();
decoder.ProgCoeffs[compIndex][((this.by * this.XNumberOfMCUs) * hi) + this.bx] = *b;
// At this point, we could execute the rest of the loop body to dequantize and
// perform the inverse DCT, to save early stages of a progressive image to the
// *image.YCbCr buffers (the whole point of progressive encoding), but in Go,
// the jpeg.Decode function does not return until the entire image is decoded,
// so we "continue" here to avoid wasted computation.
return;
}
}
// Dequantize, perform the inverse DCT and store the block to the image.
Block8x8F.UnZig(b, this.Pointers.QuantiazationTable, this.Pointers.Unzig);
DCT.TransformIDCT(ref *b, ref *this.Pointers.Temp1, ref *this.Pointers.Temp2);
var destChannel = decoder.GetDestinationChannel(compIndex);
var destArea = destChannel.GetOffsetedSubAreaForBlock(this.bx, this.by);
destArea.LoadColorsFrom(this.Pointers.Temp1, this.Pointers.Temp2);
}
} }
} }

8
src/ImageSharp/Formats/Jpg/Components/Decoder/JpegScanDecoder.md
View File

@ -16,10 +16,10 @@ are members of the `JpegScanDecoder` struct
|JpegScanDecoder | |JpegScanDecoder |
|-------------------| |-------------------|
|Variables | |Variables |
|ComponentData | |ComputationData |
|ComponentPointers | |DataPointers |
- **ComponentData** holds the "large" data blocks needed for computations (Mostly `Block8x8F`-s) - **ComputationData** holds the "large" data blocks needed for computations (Mostly `Block8x8F`-s)
- **ComponentPointers** contains pointers to the memory regions of `ComponentData` so they can be easily passed around to pointer based utility methods of `Block8x8F` - **DataPointers** contains pointers to the memory regions of `ComponentData` so they can be easily passed around to pointer based utility methods of `Block8x8F`

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