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Saturday, September 19, 2020
Friday, September 18, 2020
C# .NET How to get image dimensions from header of webP for all formats; lossy, lossless, extended - partially load image
Get image dimensions from header of WebP for all formats; lossy, lossless and extended and is fast.
Code for reading the header of WebP formats is not commonly available in C# .NET, so I had to go to the WebP Container Specification to build out the code. The code reads the 1st 30 bytes of a webp file only. This is fast, but could be faster, stay tuned.
Geneva Drive.webp
Handles animated webp formats as specified by "VP8X" type.
Source Code
using System; using System.Net; using System.Collections.Generic; using System.IO; using System.Drawing; using System.Linq; using System.Diagnostics; public class Program { //Org https://www.codeproject.com/Articles/35978/Reading-Image-Headers-to-Get-Width-and-Height //Mod https://stackoverflow.com/questions/111345/getting-image-dimensions-without-reading-the-entire-file/60667939#60667939 // DecodeWebP reads only lossless :( //My version improved DecodeWebP method to read all webp formats; lossy, lossless and extended. 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)) { 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 riff = binaryReader.ReadBytes(4); //already offset 4 bytes to read R I F F uint size = binaryReader.ReadUInt32() + 8; // Size - start at offset 4, length+8! https://en.wikipedia.org/wiki/WebP - actual not on disk size var webp = binaryReader.ReadBytes(4); // start 8 offset - https://en.wikipedia.org/wiki/WebP if (webp[0] != 87 && webp[1] != 69 && webp[2] != 66 && webp[3] != 80) //must match W E B P return new Size(0, 0); //or use binaryReader.ReadBytes(8); to avoid skip above var type = binaryReader.ReadBytes(4); // start 12 offset - VP8[ ] determination string VP8Type = System.Text.Encoding.UTF8.GetString(type); Console.WriteLine("VP8Type=\""+VP8Type+"\" of size "+ size.ToString("#,##0")+" bytes."); int x = 0; int y = 0; if (VP8Type == "VP8X") //Extra format - https://developers.google.com/speed/webp/docs/riff_container#extended_file_format { //skip 32 bits or 8 bytes for Alpha, Exif, XMP flags... in VP8X header binaryReader.ReadBytes(8); 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) return 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 this //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 || $b2 != 0x2a-> 42 if (frameTag[0] != 157 || frameTag[1] != 1 || frameTag[2] != 42) return new Size(0, 0); //invalid webp file //reads 2 bytes which is 16-bits, but we want only 14 bits, shrink x = binaryReader.ReadUInt16() & 0x3fff; //$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://file-examples-com.github.io/uploads/2020/03/file_example_WEBP_1500kB.webp"; //1.5 Mb string webpfile = GetFileNameFromURL(webpURL); Size webpSize = new Size(); WebClient wc = new WebClient(); using (MemoryStream stream = new MemoryStream(wc.DownloadData(webpURL))) //this would normally be a path, but can't do that here { sw.Start(); webpSize = ImageHelper.GetDimensions(stream); sw.Stop(); } Console.WriteLine("WebP file \"{0}\" has dimensions [{1}w X {2}h] in {3}ms.", webpfile, webpSize.Width, webpSize.Height, sw.ElapsedMilliseconds); } }
Blade Runner.webp
Wednesday, September 9, 2020
C# .NET - How to get a string between two strings, minimal spanning, fast
Here's an implementation to get a string between two strings fast, which meets most expectations what this function should return. It finds the sub-string found "after" the 1st string "before" the next 2nd string. The sticky question is where does before 2nd string exactly start?
Technically, this minimal spanning meaning the string returned is the minimal length found string between the 1st string end and the beginning of the 2nd string.
Below we compare the 2nd string starting immediately after leaving no space after 1st, versus, 2nd string starting immediately after 1st but starting +1 character or next character after. We want at least one character to return, not empty string. Right.
Immediate after is how most examples are commonly implemented, but it may not be what you want, see comparison image below. Quick note, r stands for rule, see code.
With index immediately after "Exact in charts", getting string between strings "a" to "a" for input "aaaa" is empty! Technically correct.
With index immediately after "+1 in charts", getting string between strings "a" to "a" for input "aaaa" is "a". Intuitively you would want this.
Whilst the "+1" seems good, there are repercussions, in some cases might not be want you expect. Best to see it for you own eyes, in comparison chart image below.
To see full effects, run code below for "Exact" or Edit in .NET Fiddle
to try "+1" version.
using System;using System.Diagnostics; public static class Extensions { /// <summary> /// Get a substring between two anchor strings, minimal span /// </summary> /// <param name="s">source string</param> /// <param name="from">search from end of this string</param> /// <param name="to">to beginning of this string, searching backwards, from end to start of s</param> /// <returns>a substring between from and to, maximal span</returns> public static string GetFirstStringBetweenStringsMinSpanCleanup(this string s, string from, string to) { if (string.IsNullOrEmpty(s) || string.IsNullOrEmpty(from) || string.IsNullOrEmpty(to)) return string.Empty; int idxFrom = s.IndexOf(from); int idxStart = idxFrom + from.Length; //we filter "not found" -1, never race condtn if (idxFrom == -1 || idxStart >= s.Length - 1) return string.Empty; int idxEnd = s.IndexOf(to, idxStart); //Exact definition, but intuitively next line meets likely expectations -> YOU CHOOSE //int idxEnd = s.IndexOf(to, idxStart + 1); //Start next position after, leaving a space for 1 character to be returned if (idxEnd == -1 || idxEnd <= idxStart) return string.Empty; return s.Substring(idxStart, idxEnd - idxStart); } /// <summary> /// Get a substring between two anchor strings, MINIMAL SPAN /// </summary> /// <param name="s">source string</param> /// <param name="from">search from end of this string</param> /// <param name="to">to beginning of this string, searching backwards, from end to start of s</param> /// <returns>a substring between from and to, maximal span</returns> public static string GetFirstStringBetweenStringsMinSpan(this string s, string from, string to) { Console.Write("args from {0} to {1} = ", from, to); //debug //edge cases if (string.IsNullOrEmpty(s) || string.IsNullOrEmpty(from) || string.IsNullOrEmpty(to)) return string.Empty; //if (from.Length >= s.Length || to.Length >= s.Length) return string.Empty; //redundant, this Rule take care of below int idxFrom = s.IndexOf(from); int idxStart = idxFrom + from.Length; //we filter "not found" -1, never race condtn if (idxFrom == -1) return string.Empty; else if (idxStart >= s.Length - 1) //for testing combine to 1 line, we combining a idx with a length, and w/ lengths we normally subtract 1 { Console.WriteLine("r1. idxStart={0} >= (s.Length - 1)={1}", idxStart, s.Length - 1); return string.Empty; } int idxEnd = s.IndexOf(to, idxStart); //Exact definition, but intuitively next line meets likely expectations -> YOU CHOOSE //int idxEnd = s.IndexOf(to, idxStart + 1); //Start next position after, leaving a space for 1 character to be returned if (idxEnd == -1 ) return string.Empty; else if (idxEnd > s.Length - 1) //Rule 2 never gets used { Console.WriteLine("r2. idxEnd={0} > (s.Length - 1)={1}", idxEnd, s.Length - 1); return string.Empty; } else if (idxEnd <= idxStart) { Console.WriteLine("r3. idxEnd={0} <= idxStart={1}", idxEnd, idxStart); return string.Empty; } return s.Substring(idxStart, idxEnd - idxStart); } } public class Program { public static void Main() { string test = "abcd"; Console.WriteLine(test); Console.WriteLine("================="); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan(null, null)); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("", "")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan(test, test)); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("", test)); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan(test,"")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("a", "a")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("a", "b")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("a", "c")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("a", "d")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("a", "e")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("e", "e")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("ab", "a")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("ab", "b")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("ab", "c")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("ab", "d")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("ab", "a")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("ab", "b")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("ab", "c")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("ab", "d")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("abc", "a")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("abc", "b")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("abc", "c")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("abc", "d")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan(test, "a")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan(test, "b")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan(test, "c")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan(test, "d")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("a","abc")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("b", "abc")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("c", "abc")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("d", "abc")); Console.WriteLine(); test = "abcdabcd"; Console.WriteLine(test); Console.WriteLine("================="); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan(null, null)); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("", "")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan(test, test)); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("", test)); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan(test, "")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("a", "a")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("a", "b")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("a", "c")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("a", "d")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("a", "e")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("e", "e")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("ab", "a")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("ab", "b")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("ab", "c")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("ab", "d")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("ab", "a")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("ab", "b")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("ab", "c")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("ab", "d")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("abc", "a")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("abc", "b")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("abc", "c")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("abc", "d")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan(test, "a")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan(test, "b")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan(test, "c")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan(test, "d")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("a", "abc")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("b", "abc")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("c", "abc")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("d", "abc")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("abc", "d")); //pass Console.WriteLine(); test = "aaaa"; Console.WriteLine(test); Console.WriteLine("================="); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("a", "a")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("aa", "a")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("aaa", "a")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("aaaa", "a")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("a", "a")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("a", "aa")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("a", "aaa")); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("a", "aaaa")); Console.WriteLine(); test = "aaaaaaaaaaaaaaaaaaaaaaaaaaaabbbb"; Console.WriteLine(test); Console.WriteLine("================="); Console.WriteLine(test.GetFirstStringBetweenStringsMinSpan("bbbb", "aaaa")); string result = string.Empty; Stopwatch sw = new Stopwatch(); sw.Start(); result = test.GetFirstStringBetweenStringsMinSpan("aaaaaaa", "bb"); sw.Stop(); Console.WriteLine(result); Console.WriteLine(" in " + sw.ElapsedTicks + " ticks."); } }
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