/// <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 || this.bitDepth < 8)
{
NoneFilter.Encode(rawScanline, result);
return(result);
}
// This order, while different to the enumerated order is more likely to produce a smaller sum
// early on which shaves a couple of milliseconds off the processing time.
UpFilter.Encode(rawScanline, previousScanline, this.up);
int currentSum = this.CalculateTotalVariation(this.up, int.MaxValue);
int lowestSum = currentSum;
result = this.up;
PaethFilter.Encode(rawScanline, previousScanline, this.paeth, this.bytesPerPixel);
currentSum = this.CalculateTotalVariation(this.paeth, currentSum);
if (currentSum < lowestSum)
{
lowestSum = currentSum;
result = this.paeth;
}
SubFilter.Encode(rawScanline, this.sub, this.bytesPerPixel);
currentSum = this.CalculateTotalVariation(this.sub, int.MaxValue);
if (currentSum < lowestSum)
{
lowestSum = currentSum;
result = this.sub;
}
AverageFilter.Encode(rawScanline, previousScanline, this.average, this.bytesPerPixel);
currentSum = this.CalculateTotalVariation(this.average, currentSum);
if (currentSum < lowestSum)
{
result = this.average;
}
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>
/// <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);
}
/// <summary>
/// Decodes the raw interlaced pixel data row by row
/// <see href="https://github.com/juehv/DentalImageViewer/blob/8a1a4424b15d6cc453b5de3f273daf3ff5e3a90d/DentalImageViewer/lib/jiu-0.14.3/net/sourceforge/jiu/codecs/PNGCodec.java"/>
/// </summary>
/// <typeparam name="TColor">The pixel format.</typeparam>
/// <param name="compressedStream">The compressed pixel data stream.</param>
/// <param name="pixels">The image pixel accessor.</param>
private void DecodeInterlacedPixelData <TColor>(Stream compressedStream, PixelAccessor <TColor> pixels)
where TColor : struct, IPixel <TColor>
{
byte[] previousScanline = ArrayPool <byte> .Shared.Rent(this.bytesPerScanline);
byte[] scanline = ArrayPool <byte> .Shared.Rent(this.bytesPerScanline);
try
{
for (int pass = 0; pass < 7; pass++)
{
// Zero out the scanlines, because the bytes that are rented from the arraypool may not be zero.
Array.Clear(scanline, 0, this.bytesPerScanline);
Array.Clear(previousScanline, 0, this.bytesPerScanline);
int y = Adam7FirstRow[pass];
int numColumns = this.ComputeColumnsAdam7(pass);
if (numColumns == 0)
{
// This pass contains no data; skip to next pass
continue;
}
int bytesPerInterlaceScanline = this.CalculateScanlineLength(numColumns) + 1;
while (y < this.header.Height)
{
compressedStream.Read(scanline, 0, bytesPerInterlaceScanline);
FilterType filterType = (FilterType)scanline[0];
switch (filterType)
{
case FilterType.None:
NoneFilter.Decode(scanline);
break;
case FilterType.Sub:
SubFilter.Decode(scanline, bytesPerInterlaceScanline, this.bytesPerPixel);
break;
case FilterType.Up:
UpFilter.Decode(scanline, previousScanline, bytesPerInterlaceScanline);
break;
case FilterType.Average:
AverageFilter.Decode(scanline, previousScanline, bytesPerInterlaceScanline, this.bytesPerPixel);
break;
case FilterType.Paeth:
PaethFilter.Decode(scanline, previousScanline, bytesPerInterlaceScanline, this.bytesPerPixel);
break;
default:
throw new ImageFormatException("Unknown filter type.");
}
this.ProcessInterlacedDefilteredScanline(scanline, y, pixels, Adam7FirstColumn[pass], Adam7ColumnIncrement[pass]);
Swap(ref scanline, ref previousScanline);
y += Adam7RowIncrement[pass];
}
}
}
finally
{
ArrayPool <byte> .Shared.Return(previousScanline);
ArrayPool <byte> .Shared.Return(scanline);
}
}
/// <summary>
/// Decodes the raw pixel data row by row
/// </summary>
/// <typeparam name="TColor">The pixel format.</typeparam>
/// <param name="compressedStream">The compressed pixel data stream.</param>
/// <param name="pixels">The image pixel accessor.</param>
private void DecodePixelData <TColor>(Stream compressedStream, PixelAccessor <TColor> pixels)
where TColor : struct, IPixel <TColor>
{
byte[] previousScanline = ArrayPool <byte> .Shared.Rent(this.bytesPerScanline);
byte[] scanline = ArrayPool <byte> .Shared.Rent(this.bytesPerScanline);
// Zero out the scanlines, because the bytes that are rented from the arraypool may not be zero.
Array.Clear(scanline, 0, this.bytesPerScanline);
Array.Clear(previousScanline, 0, this.bytesPerScanline);
try
{
for (int y = 0; y < this.header.Height; y++)
{
compressedStream.Read(scanline, 0, this.bytesPerScanline);
FilterType filterType = (FilterType)scanline[0];
switch (filterType)
{
case FilterType.None:
NoneFilter.Decode(scanline);
break;
case FilterType.Sub:
SubFilter.Decode(scanline, this.bytesPerScanline, this.bytesPerPixel);
break;
case FilterType.Up:
UpFilter.Decode(scanline, previousScanline, this.bytesPerScanline);
break;
case FilterType.Average:
AverageFilter.Decode(scanline, previousScanline, this.bytesPerScanline, this.bytesPerPixel);
break;
case FilterType.Paeth:
PaethFilter.Decode(scanline, previousScanline, this.bytesPerScanline, this.bytesPerPixel);
break;
default:
throw new ImageFormatException("Unknown filter type.");
}
this.ProcessDefilteredScanline(scanline, y, pixels);
Swap(ref scanline, ref previousScanline);
}
}
finally
{
ArrayPool <byte> .Shared.Return(previousScanline);
ArrayPool <byte> .Shared.Return(scanline);
}
}
/// <summary>
/// Decodes the raw interlaced pixel data row by row
/// <see href="https://github.com/juehv/DentalImageViewer/blob/8a1a4424b15d6cc453b5de3f273daf3ff5e3a90d/DentalImageViewer/lib/jiu-0.14.3/net/sourceforge/jiu/codecs/PNGCodec.java"/>
/// </summary>
/// <typeparam name="TPixel">The pixel format.</typeparam>
/// <param name="compressedStream">The compressed pixel data stream.</param>
/// <param name="image">The current image.</param>
private void DecodeInterlacedPixelData <TPixel>(Stream compressedStream, Image <TPixel> image)
where TPixel : struct, IPixel <TPixel>
{
while (true)
{
int numColumns = this.ComputeColumnsAdam7(this.pass);
if (numColumns == 0)
{
this.pass++;
// This pass contains no data; skip to next pass
continue;
}
int bytesPerInterlaceScanline = this.CalculateScanlineLength(numColumns) + 1;
while (this.currentRow < this.header.Height)
{
int bytesRead = compressedStream.Read(this.scanline.Array, this.currentRowBytesRead, bytesPerInterlaceScanline - this.currentRowBytesRead);
this.currentRowBytesRead += bytesRead;
if (this.currentRowBytesRead < bytesPerInterlaceScanline)
{
return;
}
this.currentRowBytesRead = 0;
Span <byte> scanSpan = this.scanline.Slice(0, bytesPerInterlaceScanline);
Span <byte> prevSpan = this.previousScanline.Slice(0, bytesPerInterlaceScanline);
var filterType = (FilterType)scanSpan[0];
switch (filterType)
{
case FilterType.None:
break;
case FilterType.Sub:
SubFilter.Decode(scanSpan, this.bytesPerPixel);
break;
case FilterType.Up:
UpFilter.Decode(scanSpan, prevSpan);
break;
case FilterType.Average:
AverageFilter.Decode(scanSpan, prevSpan, this.bytesPerPixel);
break;
case FilterType.Paeth:
PaethFilter.Decode(scanSpan, prevSpan, this.bytesPerPixel);
break;
default:
throw new ImageFormatException("Unknown filter type.");
}
Span <TPixel> rowSpan = image.GetRowSpan(this.currentRow);
this.ProcessInterlacedDefilteredScanline(this.scanline.Array, rowSpan, Adam7FirstColumn[this.pass], Adam7ColumnIncrement[this.pass]);
Swap(ref this.scanline, ref this.previousScanline);
this.currentRow += Adam7RowIncrement[this.pass];
}
this.pass++;
this.previousScanline.Clear();
if (this.pass < 7)
{
this.currentRow = Adam7FirstRow[this.pass];
}
else
{
this.pass = 0;
break;
}
}
}