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Refactor parsing VP8X header

pull/1552/head
Brian Popow 6 years ago
parent
91fe575fb1
commit
aaa9e07416
3 changed files with 93 additions and 66 deletions
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  1. 150
      src/ImageSharp/Formats/WebP/WebPDecoderCore.cs
  2. 6
      src/ImageSharp/Formats/WebP/WebPLossyDecoder.cs
  3. 3
      tests/ImageSharp.Benchmarks/Codecs/DecodeWebp.cs

150
src/ImageSharp/Formats/WebP/WebPDecoderCore.cs
View File

@ -14,7 +14,7 @@ using SixLabors.ImageSharp.PixelFormats;
namespace SixLabors.ImageSharp.Formats.WebP
{
/// <summary>
/// Performs the bitmap decoding operation.
/// Performs the webp decoding operation.
/// </summary>
internal sealed class WebPDecoderCore
{
@ -140,6 +140,10 @@ namespace SixLabors.ImageSharp.Formats.WebP
return chunkSize;
}
/// <summary>
/// Reads information present in the image header, about the image content and how to decode the image.
/// </summary>
/// <returns>Information about the webp image.</returns>
private WebPImageInfo ReadVp8Info()
{
this.Metadata = new ImageMetadata();
@ -173,29 +177,39 @@ namespace SixLabors.ImageSharp.Formats.WebP
/// <returns>Information about this webp image.</returns>
private WebPImageInfo ReadVp8XHeader()
{
var features = new WebPFeatures();
uint chunkSize = this.ReadChunkSize();
// The first byte contains information about the image features used.
// The first two bit of it are reserved and should be 0. TODO: should an exception be thrown if its not the case, or just ignore it?
byte imageFeatures = (byte)this.currentStream.ReadByte();
// The first two bit of it are reserved and should be 0.
if (imageFeatures >> 6 != 0)
{
WebPThrowHelper.ThrowImageFormatException("first two bits of the VP8X header are expected to be zero");
}
// If bit 3 is set, a ICC Profile Chunk should be present.
bool isIccPresent = (imageFeatures & (1 << 5)) != 0;
features.IccProfile = (imageFeatures & (1 << 5)) != 0;
// If bit 4 is set, any of the frames of the image contain transparency information ("alpha" chunk).
bool isAlphaPresent = (imageFeatures & (1 << 4)) != 0;
features.Alpha = (imageFeatures & (1 << 4)) != 0;
// If bit 5 is set, a EXIF metadata should be present.
bool isExifPresent = (imageFeatures & (1 << 3)) != 0;
features.ExifProfile = (imageFeatures & (1 << 3)) != 0;
// If bit 6 is set, XMP metadata should be present.
bool isXmpPresent = (imageFeatures & (1 << 2)) != 0;
features.XmpMetaData = (imageFeatures & (1 << 2)) != 0;
// If bit 7 is set, animation should be present.
bool isAnimationPresent = (imageFeatures & (1 << 1)) != 0;
features.Animation = (imageFeatures & (1 << 1)) != 0;
// 3 reserved bytes should follow which are supposed to be zero.
this.currentStream.Read(this.buffer, 0, 3);
if (this.buffer[0] != 0 || this.buffer[1] != 0 | this.buffer[2] != 0)
{
WebPThrowHelper.ThrowImageFormatException("reserved bytes should be zero");
}
// 3 bytes for the width.
this.currentStream.Read(this.buffer, 0, 3);
@ -208,76 +222,25 @@ namespace SixLabors.ImageSharp.Formats.WebP
uint height = (uint)BinaryPrimitives.ReadInt32LittleEndian(this.buffer) + 1;
// Optional chunks ICCP, ALPH and ANIM can follow here.
WebPChunkType chunkType;
if (isIccPresent)
WebPChunkType chunkType = this.ReadChunkType();
while (IsOptionalVp8XChunk(chunkType))
{
this.ParseOptionalExtendedChunks(chunkType, features);
chunkType = this.ReadChunkType();
if (chunkType is WebPChunkType.Iccp)
{
uint iccpChunkSize = this.ReadChunkSize();
if (!this.IgnoreMetadata)
{
var iccpData = new byte[iccpChunkSize];
this.currentStream.Read(iccpData, 0, (int)iccpChunkSize);
var profile = new IccProfile(iccpData);
if (profile.CheckIsValid())
{
this.Metadata.IccProfile = profile;
}
}
else
{
this.currentStream.Skip((int)iccpChunkSize);
}
}
}
if (isAnimationPresent)
if (features.Animation)
{
this.webpMetadata.Animated = true;
// TODO: Animations are not yet supported.
return new WebPImageInfo()
{
Width = width,
Height = height,
Features = new WebPFeatures()
{
Animation = true
}
Features = features
};
}
byte[] alphaData = null;
byte alphaChunkHeader = 0;
if (isAlphaPresent)
{
chunkType = this.ReadChunkType();
if (chunkType != WebPChunkType.Alpha)
{
WebPThrowHelper.ThrowImageFormatException($"unexpected chunk type {chunkType}, expected ALPH chunk is missing");
}
uint alphaChunkSize = this.ReadChunkSize();
alphaChunkHeader = (byte)this.currentStream.ReadByte();
alphaData = new byte[alphaChunkSize - 1];
this.currentStream.Read(alphaData, 0, alphaData.Length);
}
var features = new WebPFeatures()
{
Animation = isAnimationPresent,
Alpha = isAlphaPresent,
AlphaData = alphaData,
AlphaChunkHeader = alphaChunkHeader,
ExifProfile = isExifPresent,
IccProfile = isIccPresent,
XmpMetaData = isXmpPresent
};
// A VP8 or VP8L chunk should follow here.
chunkType = this.ReadChunkType();
// TOOD: check if VP8 or VP8L info about the dimensions match VP8X info
// TODO: check if VP8 or VP8L info about the dimensions match VP8X info
switch (chunkType)
{
case WebPChunkType.Vp8:
@ -446,6 +409,47 @@ namespace SixLabors.ImageSharp.Formats.WebP
};
}
/// <summary>
/// Parses optional VP8X chunks, which can be ICCP, ANIM or ALPH chunks.
/// </summary>
/// <param name="chunkType">The chunk type.</param>
/// <param name="features">The webp image features.</param>
private void ParseOptionalExtendedChunks(WebPChunkType chunkType, WebPFeatures features)
{
switch (chunkType)
{
case WebPChunkType.Iccp:
uint iccpChunkSize = this.ReadChunkSize();
if (!this.IgnoreMetadata)
{
var iccpData = new byte[iccpChunkSize];
this.currentStream.Read(iccpData, 0, (int)iccpChunkSize);
var profile = new IccProfile(iccpData);
if (profile.CheckIsValid())
{
this.Metadata.IccProfile = profile;
}
}
else
{
this.currentStream.Skip((int)iccpChunkSize);
}
break;
case WebPChunkType.Animation:
this.webpMetadata.Animated = true;
break;
case WebPChunkType.Alpha:
uint alphaChunkSize = this.ReadChunkSize();
features.AlphaChunkHeader = (byte)this.currentStream.ReadByte();
features.AlphaData = new byte[alphaChunkSize - 1];
this.currentStream.Read(features.AlphaData, 0, features.AlphaData.Length);
break;
}
}
/// <summary>
/// Parses optional metadata chunks. There SHOULD be at most one chunk of each type ('EXIF' and 'XMP ').
/// If there are more such chunks, readers MAY ignore all except the first one.
@ -512,5 +516,21 @@ namespace SixLabors.ImageSharp.Formats.WebP
throw new ImageFormatException("Invalid WebP data.");
}
/// <summary>
/// Determines if the chunk type is an optional VP8X chunk.
/// </summary>
/// <param name="chunkType">The chunk type.</param>
/// <returns>True, if its an optional chunk type.</returns>
private static bool IsOptionalVp8XChunk(WebPChunkType chunkType)
{
return chunkType switch
{
WebPChunkType.Alpha => true,
WebPChunkType.Animation => true,
WebPChunkType.Iccp => true,
_ => false
};
}
}
}

6
src/ImageSharp/Formats/WebP/WebPLossyDecoder.cs
View File

@ -12,6 +12,12 @@ using SixLabors.ImageSharp.PixelFormats;
namespace SixLabors.ImageSharp.Formats.WebP
{
/// <summary>
/// Decoder for lossy webp images. This code is a port of libwebp, which can be found here: https://chromium.googlesource.com/webm/libwebp
/// </summary>
/// <remarks>
/// The lossy specification can be found here: https://tools.ietf.org/html/rfc6386
/// </remarks>
internal sealed class WebPLossyDecoder
{
/// <summary>

3
tests/ImageSharp.Benchmarks/Codecs/DecodeWebp.cs
View File

@ -18,9 +18,10 @@ namespace SixLabors.ImageSharp.Benchmarks.Codecs
private byte[] webpLosslessBytes;
private string TestImageLossyFullPath => Path.Combine(TestEnvironment.InputImagesDirectoryFullPath, this.TestImageLossy);
private string TestImageLosslessFullPath => Path.Combine(TestEnvironment.InputImagesDirectoryFullPath, this.TestImageLossless);
[Params(TestImages.WebP.Lossy.Bike)]
[Params(TestImages.WebP.Lossy.Alpha1)]
public string TestImageLossy { get; set; }
[Params(TestImages.WebP.Lossless.BikeThreeTransforms)]

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