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Dw 30 optimize extract alpha data and prepare byte array #125

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Merged
djrecipe merged 2 commits into from
Feb 21, 2025
Merged

Dw 30 optimize extract alpha data and prepare byte array #125

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1a69191
[DW-30] optimize ExtractAlphaData use array and index to increase speed
ikkyuland Feb 20, 2025
3872ae2
[DW-30] optimize PrepareByteArray use BlockCopy for faster copy
ikkyuland Feb 20, 2025
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54 changes: 37 additions & 17 deletions IronSoftware.Drawing/IronSoftware.Drawing.Common/AnyBitmap.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -828,20 +828,25 @@ public byte[] ExtractAlphaData()
{
if (BitsPerPixel == 32)
{
var alpha = new List<byte>(Image.Width * Image.Height);
var alpha = new byte[Image.Width * Image.Height];
int alphaIndex = 0;
using var rgbaImage = Image is Image<SixLabors.ImageSharp.PixelFormats.Rgba32> image
? image
: Image.CloneAs<SixLabors.ImageSharp.PixelFormats.Rgba32>();
rgbaImage.ProcessPixelRows(accessor =>
{
for (int y = 0; y < accessor.Height; y++)
{
Span<SixLabors.ImageSharp.PixelFormats.Rgba32> pixelRow = accessor.GetRowSpan(y);

for (int x = 0; x < pixelRow.Length; x++)
// Get the row as a span of Rgba32.
Span<Rgba32> pixelRow = accessor.GetRowSpan(y);
// Interpret the row as a span of bytes.
Span<byte> rowBytes = MemoryMarshal.AsBytes(pixelRow);

// Each pixel is 4 bytes: R, G, B, A.
// The alpha channel is the fourth byte (index 3, 7, 11, ...).
for (int i = 3; i < rowBytes.Length; i += 4)
{
SixLabors.ImageSharp.PixelFormats.Rgba32 pixel = pixelRow[x];
alpha.Add(pixel.A);
alpha[alphaIndex++] = rowBytes[i];
}
}
});
Expand Down Expand Up @@ -2332,20 +2337,35 @@ private bool IsThumbnail(Tiff tiff)

private ReadOnlySpan<byte> PrepareByteArray(Image<Rgba32> bmp, int[] raster, int width, int height)
{
byte[] bits = new byte[GetStride(bmp) * height];
int stride = GetStride(bmp);
byte[] bits = new byte[stride * height];

for (int y = 0; y < height; y++)
// If no extra padding exists, copy entire rows at once.
if (stride == width * 4 && true)
{
int rasterOffset = y * width;
int bitsOffset = (height - y - 1) * GetStride(bmp);

for (int x = 0; x < width; x++)
int bytesPerRow = stride;
for (int y = 0; y < height; y++)
{
int srcByteIndex = y * bytesPerRow;
int destByteIndex = (height - y - 1) * bytesPerRow;
Buffer.BlockCopy(raster, srcByteIndex, bits, destByteIndex, bytesPerRow);
}
}
else
{
// Fallback to per-pixel processing if stride includes padding.
for (int y = 0; y < height; y++)
{
int rgba = raster[rasterOffset++];
bits[bitsOffset++] = (byte)(rgba & 0xff); // R
bits[bitsOffset++] = (byte)((rgba >> 8) & 0xff); // G
bits[bitsOffset++] = (byte)((rgba >> 16) & 0xff); // B
bits[bitsOffset++] = (byte)((rgba >> 24) & 0xff); // A
int rasterOffset = y * width;
int bitsOffset = (height - y - 1) * stride;
for (int x = 0; x < width; x++)
{
int rgba = raster[rasterOffset++];
bits[bitsOffset++] = (byte)(rgba & 0xff); // R
bits[bitsOffset++] = (byte)((rgba >> 8) & 0xff); // G
bits[bitsOffset++] = (byte)((rgba >> 16) & 0xff); // B
bits[bitsOffset++] = (byte)((rgba >> 24) & 0xff); // A
}
}
}

Expand Down