The order to consume the header flags was clearly laid out in the Webp RIFF container specification, but getting the bits was tricky. Since even taking little-endian into account and reversing the bit values in the byte, which then aligning the indices to the spec, it still failed. Turns out it was the bit shifting math is using little-endian mode. Therefore, the flags are read in reverse order.
Blade Runner.webp animated
using System; using System.Net; using System.Collections.Generic; using System.IO; using System.Drawing; using System.Linq; using System.Diagnostics; public class Program { //https://stackoverflow.com/questions/111345/getting-image-dimensions-without-reading-the-entire-file/60667939#60667939 //DecodeWebP reads only lossless :( //My version improves DecodeWebP to read all webp formats, lossy, lossless and extended! //https://metadataconsulting.blogspot.com/2020/09/CSharp-dotNET-How-to-get-Animation-Alpha-EXIF-ICC-flags-from-header-of-WebP-image-file-partially-loaded-file.html internal static class ImageHelper { const string errorMessage = "Could not recognise image format."; private static Dictionary<byte[], Func<BinaryReader, Size>> imageFormatDecoders = new Dictionary<byte[], Func<BinaryReader, Size>>() { { new byte[] { 0x42, 0x4D }, DecodeBitmap }, { new byte[] { 0x47, 0x49, 0x46, 0x38, 0x37, 0x61 }, DecodeGif }, { new byte[] { 0x47, 0x49, 0x46, 0x38, 0x39, 0x61 }, DecodeGif }, { new byte[] { 0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A }, DecodePng }, { new byte[] { 0xff, 0xd8 }, DecodeJfif }, { new byte[] { 0x52, 0x49, 0x46, 0x46 }, DecodeWebP }, }; /// <summary> /// Gets the dimensions of an image. /// </summary> /// <param name="path">The path of the image to get the dimensions of.</param> /// <returns>The dimensions of the specified image.</returns> /// <exception cref="ArgumentException">The image was of an unrecognised format.</exception> public static Size GetDimensions(BinaryReader binaryReader) { int maxMagicBytesLength = imageFormatDecoders.Keys.OrderByDescending(x => x.Length).First().Length; byte[] magicBytes = new byte[maxMagicBytesLength]; for (int i = 0; i < maxMagicBytesLength; i += 1) { magicBytes[i] = binaryReader.ReadByte(); foreach (var kvPair in imageFormatDecoders) { if (StartsWith(magicBytes, kvPair.Key)) { Console.WriteLine(kvPair.Value.Method); return kvPair.Value(binaryReader); } } } throw new ArgumentException(errorMessage, "binaryReader"); } /// <summary> /// Gets the dimensions of an image. /// </summary> /// <param name="path">The path of the image to get the dimensions of.</param> /// <returns>The dimensions of the specified image.</returns> /// <exception cref="ArgumentException">The image was of an unrecognized format.</exception> public static Size GetDimensions(string path) { using (BinaryReader binaryReader = new BinaryReader(File.OpenRead(path))) { try { return GetDimensions(binaryReader); } catch (ArgumentException e) { if (e.Message.StartsWith(errorMessage)) { throw new ArgumentException(errorMessage, "path", e); } else { throw e; } } } } /// <summary> /// Gets the dimensions of an image. /// </summary> /// <param name="path">The path of the image to get the dimensions of.</param> /// <returns>The dimensions of the specified image.</returns> /// <exception cref="ArgumentException">The image was of an unrecognized format.</exception> public static Size GetDimensions(MemoryStream ms) { using (BinaryReader binaryReader = new BinaryReader(ms)) { try { return GetDimensions(binaryReader); } catch (ArgumentException e) { if (e.Message.StartsWith(errorMessage)) { throw new ArgumentException(errorMessage, "path", e); } else { throw e; } } } } private static bool StartsWith(byte[] thisBytes, byte[] thatBytes) { for (int i = 0; i < thatBytes.Length; i += 1) { if (thisBytes[i] != thatBytes[i]) { return false; } } return true; } private static short ReadLittleEndianInt16(BinaryReader binaryReader) { byte[] bytes = new byte[sizeof(short)]; for (int i = 0; i < sizeof(short); i += 1) { bytes[sizeof(short) - 1 - i] = binaryReader.ReadByte(); } return BitConverter.ToInt16(bytes, 0); } private static int ReadLittleEndianInt32(BinaryReader binaryReader) { byte[] bytes = new byte[sizeof(int)]; for (int i = 0; i < sizeof(int); i += 1) { bytes[sizeof(int) - 1 - i] = binaryReader.ReadByte(); } return BitConverter.ToInt32(bytes, 0); } private static Size DecodeBitmap(BinaryReader binaryReader) { binaryReader.ReadBytes(16); int width = binaryReader.ReadInt32(); int height = binaryReader.ReadInt32(); return new Size(width, height); } private static Size DecodeGif(BinaryReader binaryReader) { int width = binaryReader.ReadInt16(); int height = binaryReader.ReadInt16(); return new Size(width, height); } private static Size DecodePng(BinaryReader binaryReader) { binaryReader.ReadBytes(8); int width = ReadLittleEndianInt32(binaryReader); int height = ReadLittleEndianInt32(binaryReader); return new Size(width, height); } private static Size DecodeJfif(BinaryReader binaryReader) { while (binaryReader.ReadByte() == 0xff) { byte marker = binaryReader.ReadByte(); short chunkLength = ReadLittleEndianInt16(binaryReader); if (marker == 0xc0 || marker == 0xc2) // c2: progressive { binaryReader.ReadByte(); int height = ReadLittleEndianInt16(binaryReader); int width = ReadLittleEndianInt16(binaryReader); return new Size(width, height); } if (chunkLength < 0) { ushort uchunkLength = (ushort)chunkLength; binaryReader.ReadBytes(uchunkLength - 2); } else { binaryReader.ReadBytes(chunkLength - 2); } } throw new ArgumentException(errorMessage); } //Other libs did not do it //https://github.com/JosePineiro/WebP-wrapper/blob/master/WebPTest/WebPWrapper.cs //https://github.com/JimBobSquarePants/ImageProcessor/blob/6092da59e9aa4975e564002ef3c782a8f6bf3384/src/Plugins/ImageProcessor/ImageProcessor.Plugins.WebP/Imaging/Formats/WebPFormat.cs //fast private static Size DecodeWebP(BinaryReader binaryReader) { //https://developers.google.com/speed/webp/docs/riff_container //var riffseg = binaryReader.ReadBytes(4); //already offset 4 bytes //var sizebytes = binaryReader.ReadBytes(4); // Size var size = binaryReader.ReadUInt32(); // Size - start at offset 4 var webp = binaryReader.ReadBytes(4); // start 8 offset var type = binaryReader.ReadBytes(4); // start 12 offset - VP8[ ] determination string VP8Type = System.Text.Encoding.UTF8.GetString(type); Console.WriteLine("VP8Type=\""+VP8Type+"\""); int x = 0; int y = 0; if (VP8Type == "VP8X") //Extra format - https://developers.google.com/speed/webp/docs/riff_container#extended_file_format { binaryReader.ReadBytes(4); //skip 4 bytes byte Flags = binaryReader.ReadByte(); //read 1 byte for all header bit bFlags //////////////////////////////////////////// ///////// LITTLE INDIAN MATH! REVERSE ORDER - https://developers.google.com/speed/webp/docs/riff_container#extended_file_format //////////////////////////////////////////// int bitPos = 0; //bit position //var bitR1C = (((Flags>> bitPos) & 1) != 0); //Originally attempt at order bool bitR3C = (((Flags>> bitPos) & 1) != 0); bitPos = 1; //var bitR2C = (((Flags>> bitPos) & 1) != 0); //Originally attempt at order var bitAniC = (((Flags>> bitPos) & 1) != 0); Console.WriteLine("has Animantion ? {0}", bitAniC); bitPos = 2; //var bitICCC = (((Flags>> bitPos) & 1) != 0); //Originally attempt at order var bitXMPC = (((Flags>> bitPos) & 1) != 0); Console.WriteLine("has XMP ? {0}", bitXMPC); bitPos = 3; //var bitAlphaC = (Flags>> bitPos) & 1; //Originally attempt at order bool bitExifC = (((Flags>> bitPos) & 1) != 0); Console.WriteLine("has EXIF ? {0}", bitExifC); bitPos = 4; //var bitExifC = (((Flags>> bitPos) & 1) != 0); //Originally attempt at order var bitAlphaC = (((Flags>> bitPos) & 1) != 0); Console.WriteLine("has Alpha ? {0}", bitAlphaC); bitPos = 5; //var bitXMPC = (((Flags>> bitPos) & 1) != 0);//Originally attempt at order var bitICCC = (((Flags>> bitPos) & 1) != 0); Console.WriteLine("has ICC ? {0}", bitAniC); bitPos = 6; //var bitAniC = (((Flags>> bitPos) & 1) != 0); //Originally attempt at order var bitR2C = (((Flags>> bitPos) & 1) != 0); bitPos = 7; //var bitR3C = (Flags>> bitPos) & 1; //Originally attempt at order var bitR1C = (((Flags>> bitPos) & 1) != 0); binaryReader.ReadBytes(3); byte[] w = binaryReader.ReadBytes(3); //24bits for width x = 1 + (w[2] << 16 | w[1] << 8 | w[0]); //little endian byte[] h = binaryReader.ReadBytes(3); //24bits for height y = 1 + (h[2] << 16 | h[1] << 8 | h[0]); return new Size(x, y); } else if (VP8Type == "VP8L") //Lossless - https://developers.google.com/speed/webp/docs/webp_lossless_bitstream_specification#2_riff_header { binaryReader.ReadBytes(4); //size byte[] sig = binaryReader.ReadBytes(1); //0x2f->47 1 byte signature if (sig[0] != 47) new Size(0, 0); byte[] wh = binaryReader.ReadBytes(4); //width and height in 1 read x = 1 + (((wh[1] & 0x3F) << 8) | wh[0]); //{1 + ((($b1 & 0x3F) << 8) | $b0)} - https://blog.tcl.tk/38137 y = 1 + (((wh[3] & 0xF) << 10) | (wh[2] << 2) | ((wh[1] & 0xC0) >> 6)); //{1 + ((($b3 & 0xF) << 10) | ($b2 << 2) | (($b1 & 0xC0) >> 6))}] return new Size(x, y); } else if (VP8Type == "VP8 ") //Lossy - https://tools.ietf.org/html/rfc6386#section-9.1 { //Lossy - https://tools.ietf.org/html/rfc6386#section-9.1 hard to decipher //pc->Width = swap2(*(unsigned short*)(c+3))&0x3fff; 0x3fff -> 16383 decimal swap2 - big or little indian depending on machine //pc->Height = swap2(*(unsigned short*)(c+5))&0x3fff; //https://blog.tcl.tk/38137 - much better binaryReader.ReadBytes(7); //move to offset 23 or 0x17, 23-12+4=7 - open webp lossy file https://developers.google.com/speed/webp/gallery1 byte[] frameTag = binaryReader.ReadBytes(3); //$b0 != 0x9d->157 || $b1 != 0x01>1 || $b2 != 0x2a-> 42 if (frameTag[0] != 157 && frameTag[0] != 1 && frameTag[0] != 42) return new Size(0, 0); //invalid webp file //reads 2-bytes which is 16-bits, but we want only 14bits, so and it to 14 bits x = binaryReader.ReadUInt16() & 0x3fff; //$width & 0x3fff -> & 0b00_11111111111111 c#7.0 above only y = binaryReader.ReadUInt16() & 0x3fff; //$height & 0x3fff return new Size(x, y); } return new Size(0, 0); } } public static string GetFileNameFromURL(string hrefLink) //hack { string[] parts = hrefLink.Split('/'); string fileName = string.Empty; if (parts.Length > 0) fileName = parts[parts.Length - 1]; else fileName = hrefLink; return fileName; } public static void Main() { Stopwatch sw = new Stopwatch(); //string webpURL = "https://www.gstatic.com/webp/gallery/1.sm.webp";//Lossy //string webpURL = "https://www.gstatic.com/webp/gallery3/2_webp_ll.webp";//Lossless string webpURL = "https://www.gstatic.com/webp/gallery3/1_webp_a.webp";//Extended with alpha channel //string webpURL = "https://mathiasbynens.be/demo/animated-webp-supported.webp"; //animated //string webpURL = "http://blog.mindworkshop.com/image/webp003.webp"; //animal //string webpURL = "https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjRmBcoRBUAhJlnH3FIJz0EMHsKl_4FFG2d9r_E2_9B8rGQwu3axAUbghJfKvEcWKxB6GmGQDwQIGQmxv4ugOHYCEtDDC3ZGNHPj7Z6nRBU2GzOk0mpraApv6Vq6C2bOXSF4r_wPI4rz6w/w640-h287/BladeRunner.webp"; //string webpURL = "https://res.cloudinary.com/demo/image/upload/fl_awebp/cell_animation.webp"; string webpfile = GetFileNameFromURL(webpURL); Size webpSize = new Size(); WebClient wc = new WebClient(); using (MemoryStream stream = new MemoryStream(wc.DownloadData(webpURL))) { sw.Start(); webpSize = ImageHelper.GetDimensions(stream); sw.Stop(); } Console.WriteLine("File \"{0}\" has dimensions [{1}w X {2}h] in {3} ms.", webpfile, webpSize.Width, webpSize.Height, sw.ElapsedMilliseconds); } }
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