/// <summary>
/// Applies all PNG filters to the given scanline and returns the filtered scanline that is deemed
/// to be most compressible, using lowest total variation as proxy for compressibility.
/// </summary>
/// <param name="rawScanline">The raw scanline</param>
/// <param name="previousScanline">The previous scanline</param>
/// <param name="result">The filtered scanline result.</param>
/// <returns>The <see cref="T:byte[]"/></returns>
private byte[] GetOptimalFilteredScanline(byte[] rawScanline, byte[] previousScanline, byte[] result)
{
// Palette images don't compress well with adaptive filtering.
if (this.PngColorType == PngColorType.Palette)
{
NoneFilter.Encode(rawScanline, result);
return(result);
}
SubFilter.Encode(rawScanline, this.sub, this.bytesPerPixel);
int currentTotalVariation = this.CalculateTotalVariation(this.sub);
int lowestTotalVariation = currentTotalVariation;
result = this.sub;
UpFilter.Encode(rawScanline, previousScanline, this.up);
currentTotalVariation = this.CalculateTotalVariation(this.up);
if (currentTotalVariation < lowestTotalVariation)
{
lowestTotalVariation = currentTotalVariation;
result = this.up;
}
AverageFilter.Encode(rawScanline, previousScanline, this.average, this.bytesPerPixel);
currentTotalVariation = this.CalculateTotalVariation(this.average);
if (currentTotalVariation < lowestTotalVariation)
{
lowestTotalVariation = currentTotalVariation;
result = this.average;
}
PaethFilter.Encode(rawScanline, previousScanline, this.paeth, this.bytesPerPixel);
currentTotalVariation = this.CalculateTotalVariation(this.paeth);
if (currentTotalVariation < lowestTotalVariation)
{
result = this.paeth;
}
return(result);
}
/// <summary>
/// Applies all PNG filters to the given scanline and returns the filtered scanline that is deemed
/// to be most compressible, using lowest total variation as proxy for compressibility.
/// </summary>
/// <param name="rawScanline">The raw scanline</param>
/// <param name="previousScanline">The previous scanline</param>
/// <param name="result">The filtered scanline result</param>
/// <param name="bytesPerScanline">The number of bytes per scanline</param>
private void GetOptimalFilteredScanline(byte[] rawScanline, byte[] previousScanline, byte[] result, int bytesPerScanline)
{
// Palette images don't compress well with adaptive filtering.
if (this.PngColorType == PngColorType.Palette)
{
NoneFilter.Encode(rawScanline, result, bytesPerScanline);
return;
}
Tuple <byte[], int>[] candidates = new Tuple <byte[], int> [4];
byte[] sub = SubFilter.Encode(rawScanline, this.bytesPerPixel, bytesPerScanline);
candidates[0] = new Tuple <byte[], int>(sub, this.CalculateTotalVariation(sub));
byte[] up = UpFilter.Encode(rawScanline, previousScanline, result, bytesPerScanline);
candidates[1] = new Tuple <byte[], int>(up, this.CalculateTotalVariation(up));
byte[] average = AverageFilter.Encode(rawScanline, previousScanline, result, this.bytesPerPixel, bytesPerScanline);
candidates[2] = new Tuple <byte[], int>(average, this.CalculateTotalVariation(average));
byte[] paeth = PaethFilter.Encode(rawScanline, previousScanline, result, this.bytesPerPixel, bytesPerScanline);
candidates[3] = new Tuple <byte[], int>(paeth, this.CalculateTotalVariation(paeth));
int lowestTotalVariation = int.MaxValue;
int lowestTotalVariationIndex = 0;
for (int i = 0; i < candidates.Length; i++)
{
if (candidates[i].Item2 < lowestTotalVariation)
{
lowestTotalVariationIndex = i;
lowestTotalVariation = candidates[i].Item2;
}
}
// ReSharper disable once RedundantAssignment
result = candidates[lowestTotalVariationIndex].Item1;
}
/// <summary>
/// Applies all PNG filters to the given scanline and returns the filtered scanline that is deemed
/// to be most compressible, using lowest total variation as proxy for compressibility.
/// </summary>
/// <param name="rawScanline">The raw scanline</param>
/// <param name="previousScanline">The previous scanline</param>
/// <param name="byteCount">The number of bytes per pixel</param>
/// <returns>The <see cref="T:byte[]"/></returns>
private byte[] GetOptimalFilteredScanline(byte[] rawScanline, byte[] previousScanline, int byteCount)
{
List <Tuple <byte[], int> > candidates = new List <Tuple <byte[], int> >();
if (this.PngColorType == PngColorType.Palette)
{
byte[] none = NoneFilter.Encode(rawScanline);
candidates.Add(new Tuple <byte[], int>(none, this.CalculateTotalVariation(none)));
}
else
{
byte[] sub = SubFilter.Encode(rawScanline, byteCount);
candidates.Add(new Tuple <byte[], int>(sub, this.CalculateTotalVariation(sub)));
byte[] up = UpFilter.Encode(rawScanline, previousScanline);
candidates.Add(new Tuple <byte[], int>(up, this.CalculateTotalVariation(up)));
byte[] average = AverageFilter.Encode(rawScanline, previousScanline, byteCount);
candidates.Add(new Tuple <byte[], int>(average, this.CalculateTotalVariation(average)));
byte[] paeth = PaethFilter.Encode(rawScanline, previousScanline, byteCount);
candidates.Add(new Tuple <byte[], int>(paeth, this.CalculateTotalVariation(paeth)));
}
int lowestTotalVariation = int.MaxValue;
int lowestTotalVariationIndex = 0;
for (int i = 0; i < candidates.Count; i++)
{
if (candidates[i].Item2 < lowestTotalVariation)
{
lowestTotalVariationIndex = i;
lowestTotalVariation = candidates[i].Item2;
}
}
return(candidates[lowestTotalVariationIndex].Item1);
}
