roadie/RoadieLibrary/Imaging/ImageHasher.cs

using SixLabors.ImageSharp;
using SixLabors.ImageSharp.Advanced;
using SixLabors.ImageSharp.PixelFormats;
using SixLabors.ImageSharp.Processing;
using System;
using System.IO;

namespace Roadie.Library.Imaging
{
    /// <summary>
    /// Contains a variety of methods useful in generating image hashes for image comparison
    /// and recognition.
    ///
    /// Credit for the AverageHash implementation to David Oftedal of the University of Oslo.
    /// </summary>
    public static class ImageHasher
    {
        #region Private constants and utility methods

        /// <summary>
        /// Bitcounts array used for BitCount method (used in Similarity comparisons).
        /// Don't try to read this or understand it, I certainly don't. Credit goes to
        /// David Oftedal of the University of Oslo, Norway for this.
        /// http://folk.uio.no/davidjo/computing.php
        /// </summary>
        private static byte[] bitCounts = {
            0,1,1,2,1,2,2,3,1,2,2,3,2,3,3,4,1,2,2,3,2,3,3,4,2,3,3,4,3,4,4,5,1,2,2,3,2,3,3,4,
            2,3,3,4,3,4,4,5,2,3,3,4,3,4,4,5,3,4,4,5,4,5,5,6,1,2,2,3,2,3,3,4,2,3,3,4,3,4,4,5,
            2,3,3,4,3,4,4,5,3,4,4,5,4,5,5,6,2,3,3,4,3,4,4,5,3,4,4,5,4,5,5,6,3,4,4,5,4,5,5,6,
            4,5,5,6,5,6,6,7,1,2,2,3,2,3,3,4,2,3,3,4,3,4,4,5,2,3,3,4,3,4,4,5,3,4,4,5,4,5,5,6,
            2,3,3,4,3,4,4,5,3,4,4,5,4,5,5,6,3,4,4,5,4,5,5,6,4,5,5,6,5,6,6,7,2,3,3,4,3,4,4,5,
            3,4,4,5,4,5,5,6,3,4,4,5,4,5,5,6,4,5,5,6,5,6,6,7,3,4,4,5,4,5,5,6,4,5,5,6,5,6,6,7,
            4,5,5,6,5,6,6,7,5,6,6,7,6,7,7,8
        };

        /// <summary>
        /// Counts bits (duh). Utility function for similarity.
        /// I wouldn't try to understand this. I just copy-pasta'd it
        /// from Oftedal's implementation. It works.
        /// </summary>
        /// <param name="num">The hash we are counting.</param>
        /// <returns>The total bit count.</returns>
        private static uint BitCount(ulong num)
        {
            uint count = 0;
            for (; num > 0; num >>= 8)
            {
                count += bitCounts[(num & 0xff)];
            }

            return count;
        }

        #endregion Private constants and utility methods

        #region Public interface methods

        /// <summary>
        /// Generate a hash for the image to be able to find like/matching images.
        /// </summary>
        /// <param name="bytes">Image bytes</param>
        /// <returns>Hash of Image</returns>
        public static ulong AverageHash(byte[] bytes)
        {
            using (Image<Rgba32> image = Image.Load(bytes))
            {
                image.Mutate(ctx => ctx.Resize(8, 8).Grayscale());
                using (var ms = new MemoryStream())
                {
                    byte[] grayscale = new byte[64];
                    uint averageValue = 0;
                    for (int y = 0; y < 8; y++)
                    {
                        Span<Rgba32> pixelRowSpan = image.GetPixelRowSpan(y);
                        for (int x = 0; x < 8; x++)
                        {
                            uint pixel = (uint)pixelRowSpan[x].PackedValue;
                            uint gray = (pixel & 0x00ff0000) >> 16;
                            gray += (pixel & 0x0000ff00) >> 8;
                            gray += (pixel & 0x000000ff);
                            gray /= 12;
                            grayscale[x + (y * 8)] = (byte)gray;
                            averageValue += gray;
                        }
                    }
                    averageValue /= 64;
                    ulong hash = 0;
                    for (int i = 0; i < 64; i++)
                    {
                        if (grayscale[i] >= averageValue)
                        {
                            hash |= (1UL << (63 - i));
                        }
                    }
                    return hash;
                }
            }
        }

        /// <summary>
        /// Computes the average hash of the image content in the given file.
        /// </summary>
        /// <param name="path">Path to the input file.</param>
        /// <returns>The hash of the input file's image content.</returns>
        public static ulong AverageHash(String path)
        {
            return AverageHash(File.ReadAllBytes(path));
        }

        public static bool ImagesAreSame(string path1, string path2)
        {
            return Similarity(path1, path2) == 100;
        }

        public static bool ImagesAreSame(byte[] image1, byte[] image2)
        {
            return Similarity(image1, image2) == 100;
        }

        /// <summary>
        /// Returns a percentage-based similarity value between the two given hashes. The higher
        /// the percentage, the closer the hashes are to being identical.
        /// </summary>
        /// <param name="hash1">The first hash.</param>
        /// <param name="hash2">The second hash.</param>
        /// <returns>The similarity percentage.</returns>
        public static double Similarity(ulong hash1, ulong hash2)
        {
            return ((64 - BitCount(hash1 ^ hash2)) * 100) / 64.0;
        }

        /// <summary>
        /// Returns a percentage-based similarity value between the image content of the two given
        /// files. The higher the percentage, the closer the image contents are to being identical.
        /// </summary>
        /// <param name="image1">The first image file.</param>
        /// <param name="image2">The second image file.</param>
        /// <returns>The similarity percentage.</returns>
        public static double Similarity(String path1, String path2)
        {
            ulong hash1 = AverageHash(path1);
            ulong hash2 = AverageHash(path2);
            return Similarity(hash1, hash2);
        }

        /// <summary>
        /// Returns a percentage-based similarity value between the image content of the two given
        /// files. The higher the percentage, the closer the image contents are to being identical.
        /// </summary>
        /// <param name="image1">The first image bytes.</param>
        /// <param name="image2">The second image bytes.</param>
        /// <returns>The similarity percentage.</returns>
        public static double Similarity(byte[] image1, byte[] image2)
        {
            ulong hash1 = AverageHash(image1);
            ulong hash2 = AverageHash(image2);
            return Similarity(hash1, hash2);
        }

        #endregion Public interface methods
    }
}