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GifEncoder: Not using the default quantizer if an input frame is alre…
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…ady indexed
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@koszeggy
koszeggy committed Dec 30, 2021
1 parent 63dfcd9 commit 7a1b9c3
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Showing 4 changed files with 71 additions and 36 deletions.
1 change: 1 addition & 0 deletions KGySoft.Drawing/Drawing/Imaging/Palette.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -241,6 +241,7 @@ private static Color32[] Grayscale4Palette
internal bool HasAlpha { get; }
internal bool HasMultiLevelAlpha { get; }
internal int TransparentIndex { get; }
internal bool HasTransparent => TransparentIndex >= 0;

#endregion

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89 changes: 53 additions & 36 deletions KGySoft.Drawing/Drawing/Imaging/_Encoders/GifEncoder.FramesEnumerator.cs
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Expand Up @@ -17,7 +17,6 @@

using System;
using System.Collections.Generic;
using System.Diagnostics.CodeAnalysis;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
Expand Down Expand Up @@ -162,7 +161,7 @@ internal SuppressSubTaskProgressContext(IAsyncContext asyncContext)
#region Properties

#region Internal Properties

internal IReadableBitmapData? Frame => current.BitmapData;
internal Point Location => current.Location;
internal int Delay => current.Delay;
Expand All @@ -172,28 +171,15 @@ internal SuppressSubTaskProgressContext(IAsyncContext asyncContext)

#region Private Properties

private bool QuantizerSupportsTransparency
private byte AlphaThreshold
{
get
{
if (quantizerProperties.Initialized)
return quantizerProperties.SupportsTransparency;

quantizerProperties.Initialized = true;

// the default Wu quantizer supports transparency
if (config.Quantizer == null)
{
quantizerProperties.SupportsTransparency = true;
quantizerProperties.AlphaThreshold = 128;
return true;
}
if (!quantizerProperties.Initialized)
CanMakeFrameTransparent(null);

// we have to test the quantizer with a single pixel
using IQuantizingSession session = quantizer.Initialize(new SolidBitmapData(new Size(1, 1), default));
quantizerProperties.SupportsTransparency = session.GetQuantizedColor(default).A == 0;
quantizerProperties.AlphaThreshold = quantizerProperties.SupportsTransparency ? session.AlphaThreshold : (byte)0;
return quantizerProperties.SupportsTransparency;
Debug.Assert(quantizerProperties.SupportsTransparency, "Not expected to be called if transparency is not supported");
return quantizerProperties.AlphaThreshold;
}
}

Expand Down Expand Up @@ -264,7 +250,7 @@ static void ProcessRowArgbWithTolerance(IReadWriteBitmapDataRow rowPrev, IReadWr
#endregion

Debug.Assert(previousFrame.GetSize() == deltaFrame.GetSize());
Debug.Assert(deltaFrame.HasAlpha());
Debug.Assert(deltaFrame.SupportsTransparency());

int transparentIndex = deltaFrame.Palette?.TransparentIndex ?? -1;

Expand Down Expand Up @@ -315,7 +301,8 @@ static void ProcessRowArgbWithTolerance(IReadWriteBitmapDataRow rowPrev, IReadWr
private static bool HasNewTransparentPixel(IReadableBitmapData currentFrame, IReadableBitmapData nextFrame, byte alphaThreshold, out Rectangle region)
{
Debug.Assert(currentFrame.GetSize() == nextFrame.GetSize());
Debug.Assert(nextFrame.HasAlpha());
Debug.Assert(nextFrame.SupportsTransparency());
Debug.Assert(alphaThreshold > 0);
region = new Rectangle(Point.Empty, currentFrame.GetSize());

IReadableBitmapDataRow rowCurrent = currentFrame.FirstRow;
Expand Down Expand Up @@ -432,7 +419,7 @@ public void Dispose()

// Using a global palette only if we know that the quantizer uses always the same colors or when the first frame
// can have transparency. If the first frame is not transparent, then some decoders (like GDI+) use a solid color when clearing frames.
Palette? globalPalette = config.Quantizer is PredefinedColorsQuantizer || firstFrame.Palette!.HasAlpha ? firstFrame.Palette : null;
Palette? globalPalette = config.Quantizer is PredefinedColorsQuantizer || firstFrame.Palette!.HasTransparent ? firstFrame.Palette : null;

return new GifEncoder(stream, logicalScreenSize)
{
Expand Down Expand Up @@ -512,13 +499,43 @@ internal void ReportProgress()

#region Private Methods

private bool CanMakeFrameTransparent(IReadableBitmapData? bitmapData)
{
if (!config.AllowDeltaFrames)
return false;

// there is no explicit quantizer: depends on current frame because palette of already indexed frames are preserved
if (config.Quantizer == null && bitmapData != null)
{
// non indexed frames will be quantized by default Wu quantizer that supports transparency
return !bitmapData.PixelFormat.IsIndexed() || bitmapData.SupportsTransparency();
}

if (quantizerProperties.Initialized)
return quantizerProperties.SupportsTransparency;

quantizerProperties.Initialized = true;

// the default Wu quantizer supports transparency
if (config.Quantizer == null)
{
quantizerProperties.SupportsTransparency = true;
quantizerProperties.AlphaThreshold = 128;
return true;
}

// we have to test the quantizer with a single pixel
using IQuantizingSession session = quantizer.Initialize(new SolidBitmapData(new Size(1, 1), default));
quantizerProperties.SupportsTransparency = session.GetQuantizedColor(default).A == 0;
quantizerProperties.AlphaThreshold = quantizerProperties.SupportsTransparency ? session.AlphaThreshold : (byte)0;
return quantizerProperties.SupportsTransparency;
}

/// <summary>
/// It consumes <see cref="nextPreparedFrame"/> set by <see cref="MoveNextPreparedFrame"/>, and sets <see cref="nextGeneratedFrame"/>.
/// Tries to generate the next frame, but it does not set <see cref="Frame"/>
/// (it is done by <see cref="MoveNext"/>) so it can look one frame forward.
/// </summary>
[SuppressMessage("Microsoft.Maintainability", "CA1502: Avoid excessive complexity",
Justification = "It would be OK without the frequent asyncContext.IsCancellationRequested checks, it's not worth the refactoring")]
private bool MoveNextGeneratedFrame()
{
Debug.Assert(nextGeneratedFrame.BitmapData == null, "MoveNextGeneratedFrame was called without processing last result by MoveNext");
Expand All @@ -535,11 +552,11 @@ private bool MoveNextGeneratedFrame()
IReadWriteBitmapData preprocessedFrame = preparedFrame.BitmapData;

// 1.) Generating delta image if needed
if (config.AllowDeltaFrames && !deltaBuffer.IsCleared && deltaBuffer.BitmapData != null && QuantizerSupportsTransparency)
if (deltaBuffer.BitmapData != null && !deltaBuffer.IsCleared && CanMakeFrameTransparent(preprocessedFrame))
{
Debug.Assert(preparedFrame.BitmapData.HasAlpha(), "Frame is not prepared correctly for delta image");
Debug.Assert(preprocessedFrame.SupportsTransparency(), "Frame is not prepared correctly for delta image");
Debug.Assert(!preparedFrame.IsQuantized, "Prepared image must not be quantized yet if delta image is created");
ClearUnchangedPixels(asyncContext, deltaBuffer.BitmapData, preprocessedFrame, config.DeltaTolerance, quantizerProperties.AlphaThreshold);
ClearUnchangedPixels(asyncContext, deltaBuffer.BitmapData, preprocessedFrame, config.DeltaTolerance, AlphaThreshold);
}

// 2.) Quantizing if needed (when source is not indexed, quantizer is specified or indexed source uses multiple transparent indices)
Expand All @@ -558,7 +575,7 @@ private bool MoveNextGeneratedFrame()

// 3.) Trim border (important: after quantizing so possible partially transparent pixels have their final state)
var contentArea = new Rectangle(Point.Empty, logicalScreenSize);
if (!config.EncodeTransparentBorders && quantizedFrame.HasAlpha())
if (!config.EncodeTransparentBorders && quantizedFrame.SupportsTransparency())
{
// Determining the actual content without the transparent border.
// If delta is allowed and clearing is needed, then this area will be expanded later
Expand All @@ -569,7 +586,7 @@ private bool MoveNextGeneratedFrame()
var disposeMethod = GifGraphicDisposalMethod.DoNotDispose;

// If frames can be transparent, then clearing might be needed after frames
if (QuantizerSupportsTransparency)
if (CanMakeFrameTransparent(null))
{
// if delta is allowed, then clearing only if a new transparent pixel appears in the next frame (that wasn't transparent before)
if (config.AllowDeltaFrames)
Expand All @@ -585,8 +602,8 @@ private bool MoveNextGeneratedFrame()
return false;
}

if (MoveNextPreparedFrame() && nextPreparedFrame.BitmapData!.HasAlpha() && HasNewTransparentPixel(
deltaBuffer.BitmapData, nextPreparedFrame.BitmapData!, quantizerProperties.AlphaThreshold, out Rectangle toClearRegion))
if (MoveNextPreparedFrame() && nextPreparedFrame.BitmapData!.SupportsTransparency() && HasNewTransparentPixel(
deltaBuffer.BitmapData, nextPreparedFrame.BitmapData!, AlphaThreshold, out Rectangle toClearRegion))
{
disposeMethod = GifGraphicDisposalMethod.RestoreToBackground;
contentArea = Rectangle.Union(contentArea, toClearRegion);
Expand Down Expand Up @@ -676,10 +693,10 @@ private bool MoveNextPreparedFrame()
// Delta frames can be used if allowed and the quantizer can use transparent colors.
// We cannot rely on renderBuffer.IsCleared here because a forward reading is used even to determine whether to clear
// so if we have a render buffer (it's not the first frame), then we must assume that delta image can be used.
bool canUseDelta = config.AllowDeltaFrames && QuantizerSupportsTransparency && deltaBuffer.BitmapData != null;
bool canUseDelta = deltaBuffer.BitmapData != null && CanMakeFrameTransparent(inputFrame);

PixelFormat preparedPixelFormat = !canUseDelta ? PixelFormat.Format8bppIndexed // can't use delta: we can already quantize
: inputFrame.HasAlpha() && inputFrame.PixelFormat.ToBitsPerPixel() <= 32 ? inputFrame.PixelFormat // we have transparency: we can use the original format
: inputFrame.SupportsTransparency() && inputFrame.PixelFormat.ToBitsPerPixel() <= 32 ? inputFrame.PixelFormat // we have transparency: we can use the original format
: PixelFormat.Format32bppArgb; // we have to add transparency (or have to reduce bpp)

// If cannot use delta image, then we can already quantize the frame.
Expand Down Expand Up @@ -713,12 +730,12 @@ private bool MoveNextPreparedFrame()
// We can use the calculated settings if the target pixel format supports alpha.
// If the target format is indexed, then using it only if we can re-use the source palette (when there is no quantizer)
// because we cannot create a new bitmap data with a palette that is created while quantizing
if (preparedPixelFormat.HasAlpha() || preparedQuantizer == null && inputFrame.Palette?.HasAlpha == true)
if (preparedPixelFormat.HasAlpha() || preparedQuantizer == null && inputFrame.Palette?.HasTransparent == true)
{
preparedFrame = BitmapDataFactory.CreateBitmapData(logicalScreenSize, preparedPixelFormat, inputFrame.Palette);

// if the source is indexed and transparent index is not 0, then we must clear the indexed image to be transparent
if (inputFrame.Palette?.TransparentIndex > 0)
if (inputFrame.Palette?.HasTransparent == true)
{
preparedFrame.DoClear(asyncContext, default);
if (asyncContext.IsCancellationRequested)
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6 changes: 6 additions & 0 deletions KGySoft.Drawing/Drawing/Imaging/_Extensions/BitmapDataExtensions.cs
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Expand Up @@ -62,6 +62,12 @@ internal static bool HasAlpha(this IBitmapData bitmapData)
return pixelFormat.HasAlpha() || pixelFormat.IsIndexed() && bitmapData.Palette?.HasAlpha == true;
}

internal static bool SupportsTransparency(this IBitmapData bitmapData)
{
PixelFormat pixelFormat = bitmapData.PixelFormat;
return pixelFormat.HasAlpha() || pixelFormat.IsIndexed() && bitmapData.Palette?.HasTransparent == true;
}

#endregion

#region Private Methods
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11 changes: 11 additions & 0 deletions KGySoft.Drawing/changelog.txt
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Expand Up @@ -5,6 +5,17 @@
+ New feature
===============================================================================

~~~~~~~~~
- v6.2.1:
~~~~~~~~~

- KGySoft.Drawing.Imaging namespace
===================================
- GifEncoder class:
- EncodeAnimation method: If quantizer is not set but the input image is already indexed, then not using the
default Wu quantizer on the input frame.


~~~~~~~~~
* v6.2.0:
~~~~~~~~~
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