From f8256e3d8d3ace23e3aa6c687a643fb7a461a69e Mon Sep 17 00:00:00 2001 From: James Jackson-South Date: Fri, 6 Jul 2018 17:40:09 +1000 Subject: [PATCH] Properly handle png resolution. --- .../Jpeg/PdfJsPort/PdfJsJpegDecoderCore.cs | 2 +- src/ImageSharp/Formats/Png/PngConstants.cs | 6 +++ src/ImageSharp/Formats/Png/PngDecoderCore.cs | 35 ++++++++++++--- src/ImageSharp/Formats/Png/PngEncoderCore.cs | 44 +++++++++++++++---- 4 files changed, 73 insertions(+), 14 deletions(-) diff --git a/src/ImageSharp/Formats/Jpeg/PdfJsPort/PdfJsJpegDecoderCore.cs b/src/ImageSharp/Formats/Jpeg/PdfJsPort/PdfJsJpegDecoderCore.cs index be2af7a3a7..8e2db4e8e9 100644 --- a/src/ImageSharp/Formats/Jpeg/PdfJsPort/PdfJsJpegDecoderCore.cs +++ b/src/ImageSharp/Formats/Jpeg/PdfJsPort/PdfJsJpegDecoderCore.cs @@ -425,7 +425,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.PdfJsPort : 0; byte units = this.MetaData.ExifProfile.TryGetValue(ExifTag.ResolutionUnit, out ExifValue resolutionTag) - ? (byte)(((ushort)resolutionTag.Value) - 1) // EXIF is 1,2,3 + ? (byte)(((ushort)resolutionTag.Value) - 1) // ExifTag.ResolutionUnit values are 1, 2, 3 : byte.MinValue; if (horizontalValue > 0 && verticalValue > 0) diff --git a/src/ImageSharp/Formats/Png/PngConstants.cs b/src/ImageSharp/Formats/Png/PngConstants.cs index ff25e26b7a..df0e16a17b 100644 --- a/src/ImageSharp/Formats/Png/PngConstants.cs +++ b/src/ImageSharp/Formats/Png/PngConstants.cs @@ -41,5 +41,11 @@ namespace SixLabors.ImageSharp.Formats.Png /// The header bytes as a big endian coded ulong. /// public const ulong HeaderValue = 0x89504E470D0A1A0AUL; + + /// + /// The number of inches in a meter. Used for converting PPM to PPI in . + /// One inch is equal to exactly 0.0254 meters. + /// + public const double InchesInMeter = 1 / 0.0254D; } } \ No newline at end of file diff --git a/src/ImageSharp/Formats/Png/PngDecoderCore.cs b/src/ImageSharp/Formats/Png/PngDecoderCore.cs index 04d4f057ce..f95b9970ad 100644 --- a/src/ImageSharp/Formats/Png/PngDecoderCore.cs +++ b/src/ImageSharp/Formats/Png/PngDecoderCore.cs @@ -233,7 +233,7 @@ namespace SixLabors.ImageSharp.Formats.Png this.ValidateHeader(); break; case PngChunkType.Physical: - this.ReadPhysicalChunk(metadata, chunk.Data.Array); + this.ReadPhysicalChunk(metadata, chunk.Data.GetSpan()); break; case PngChunkType.Data: if (image == null) @@ -307,7 +307,7 @@ namespace SixLabors.ImageSharp.Formats.Png this.ValidateHeader(); break; case PngChunkType.Physical: - this.ReadPhysicalChunk(metadata, chunk.Data.Array); + this.ReadPhysicalChunk(metadata, chunk.Data.GetSpan()); break; case PngChunkType.Data: this.SkipChunkDataAndCrc(chunk); @@ -396,9 +396,34 @@ namespace SixLabors.ImageSharp.Formats.Png /// The data containing physical data. private void ReadPhysicalChunk(ImageMetaData metadata, ReadOnlySpan data) { - // 39.3700787 = inches in a meter. - metadata.HorizontalResolution = BinaryPrimitives.ReadInt32BigEndian(data.Slice(0, 4)) / 39.3700787d; - metadata.VerticalResolution = BinaryPrimitives.ReadInt32BigEndian(data.Slice(4, 4)) / 39.3700787d; + // The pHYs chunk specifies the intended pixel size or aspect ratio for display of the image. It contains: + // Pixels per unit, X axis: 4 bytes (unsigned integer) + // Pixels per unit, Y axis: 4 bytes (unsigned integer) + // Unit specifier: 1 byte + // + // The following values are legal for the unit specifier: + // 0: unit is unknown + // 1: unit is the meter + // + // When the unit specifier is 0, the pHYs chunk defines pixel aspect ratio only; the actual size of the pixels remains unspecified. + // Conversion note: one inch is equal to exactly 0.0254 meters. + int hResolution = BinaryPrimitives.ReadInt32BigEndian(data.Slice(0, 4)); + int vResolution = BinaryPrimitives.ReadInt32BigEndian(data.Slice(4, 4)); + byte unit = data[8]; + + if (unit == byte.MinValue) + { + metadata.HorizontalResolution = hResolution; + metadata.VerticalResolution = vResolution; + metadata.ResolutionUnits = ResolutionUnits.AspectRatio; + return; + } + + // Use PPI for its commonality. + const double inchesInMeter = PngConstants.InchesInMeter; + metadata.HorizontalResolution = hResolution / inchesInMeter; + metadata.VerticalResolution = vResolution / inchesInMeter; + metadata.ResolutionUnits = ResolutionUnits.PixelsPerInch; } /// diff --git a/src/ImageSharp/Formats/Png/PngEncoderCore.cs b/src/ImageSharp/Formats/Png/PngEncoderCore.cs index 69f04979cf..6aef2a4d9e 100644 --- a/src/ImageSharp/Formats/Png/PngEncoderCore.cs +++ b/src/ImageSharp/Formats/Png/PngEncoderCore.cs @@ -8,6 +8,7 @@ using System.Linq; using SixLabors.ImageSharp.Advanced; using SixLabors.ImageSharp.Formats.Png.Filters; using SixLabors.ImageSharp.Formats.Png.Zlib; +using SixLabors.ImageSharp.MetaData; using SixLabors.ImageSharp.PixelFormats; using SixLabors.ImageSharp.Processing.Processors.Quantization; using SixLabors.Memory; @@ -598,19 +599,46 @@ namespace SixLabors.ImageSharp.Formats.Png private void WritePhysicalChunk(Stream stream, Image image) where TPixel : struct, IPixel { - if (image.MetaData.HorizontalResolution > 0 && image.MetaData.VerticalResolution > 0) + // The pHYs chunk specifies the intended pixel size or aspect ratio for display of the image. It contains: + // Pixels per unit, X axis: 4 bytes (unsigned integer) + // Pixels per unit, Y axis: 4 bytes (unsigned integer) + // Unit specifier: 1 byte + // + // The following values are legal for the unit specifier: + // 0: unit is unknown + // 1: unit is the meter + // + // When the unit specifier is 0, the pHYs chunk defines pixel aspect ratio only; the actual size of the pixels remains unspecified. + // Conversion note: one inch is equal to exactly 0.0254 meters. + ImageMetaData meta = image.MetaData; + Span hResolution = this.chunkDataBuffer.AsSpan(0, 4); + Span vResolution = this.chunkDataBuffer.AsSpan(4, 4); + switch (meta.ResolutionUnits) { - // 39.3700787 = inches in a meter. - int dpmX = (int)Math.Round(image.MetaData.HorizontalResolution * 39.3700787D); - int dpmY = (int)Math.Round(image.MetaData.VerticalResolution * 39.3700787D); + case ResolutionUnits.AspectRatio: - BinaryPrimitives.WriteInt32BigEndian(this.chunkDataBuffer.AsSpan(0, 4), dpmX); - BinaryPrimitives.WriteInt32BigEndian(this.chunkDataBuffer.AsSpan(4, 4), dpmY); + this.chunkDataBuffer[8] = 0; + BinaryPrimitives.WriteInt32BigEndian(hResolution, (int)Math.Round(meta.HorizontalResolution)); + BinaryPrimitives.WriteInt32BigEndian(vResolution, (int)Math.Round(meta.HorizontalResolution)); + break; + + case ResolutionUnits.PixelsPerCentimeter: - this.chunkDataBuffer[8] = 1; + this.chunkDataBuffer[8] = 1; + const int CmInMeter = 100; + BinaryPrimitives.WriteInt32BigEndian(hResolution, (int)Math.Round(meta.HorizontalResolution * CmInMeter)); + BinaryPrimitives.WriteInt32BigEndian(vResolution, (int)Math.Round(meta.HorizontalResolution * CmInMeter)); + break; - this.WriteChunk(stream, PngChunkType.Physical, this.chunkDataBuffer, 0, 9); + default: + + this.chunkDataBuffer[8] = 1; + BinaryPrimitives.WriteInt32BigEndian(hResolution, (int)Math.Round(meta.HorizontalResolution * PngConstants.InchesInMeter)); + BinaryPrimitives.WriteInt32BigEndian(vResolution, (int)Math.Round(meta.HorizontalResolution * PngConstants.InchesInMeter)); + break; } + + this.WriteChunk(stream, PngChunkType.Physical, this.chunkDataBuffer, 0, 9); } ///