How to dither an image

How to dither an image

         To edit an image with Dithering method you can specify `ThresholdDithering` or `FloydSteinbergDithering` options. The `ThresholdDitherig` is a simple and fast dithering method, and the `FloydSteinbergDithering` is a more complex method that takes into account nearest neighbors' pixels' intensity values. And as a second parameter, you can indicate the color palette in bits for use for dithering. More bits mean a higher quality of the resulting image, but at the same time a larger image size:

using Aspose.Imaging;
using Aspose.Imaging.FileFormats.Bmp;
using Aspose.Imaging.FileFormats.Dicom;
using Aspose.Imaging.FileFormats.Emf;
using Aspose.Imaging.FileFormats.Jpeg;
using Aspose.Imaging.FileFormats.Jpeg2000;
using Aspose.Imaging.FileFormats.Png;
using Aspose.Imaging.FileFormats.Psd;
using Aspose.Imaging.FileFormats.Tiff.Enums;
using Aspose.Imaging.ImageFilters.FilterOptions;
using Aspose.Imaging.ImageOptions;
using Aspose.Imaging.Masking;
using Aspose.Imaging.Masking.Options;
using Aspose.Imaging.Masking.Result;
using Aspose.Imaging.Sources;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;

string templatesFolder = @"c:\Users\USER\Downloads";

ThresholdDithering();

void FloydSteinbergDithering()
{
    FilterImages(image =>
    {
        //https://apireference.aspose.com/imaging/net/aspose.imaging/ditheringmethod
        image.Dither(DitheringMethod.FloydSteinbergDithering, 4);
    }, "floydsteinbergdithering");
}

void ThresholdDithering()
{
    FilterImages(image =>
    {
        //https://apireference.aspose.com/imaging/net/aspose.imaging/ditheringmethod
        image.Dither(DitheringMethod.ThresholdDithering, 4);
    }, "thresholddithering");
}

void FilterImages(Action<RasterImage> doFilter, string filterName)
{
    List<string> rasterFormats = new List<string>() { "jpg", "png", "bmp", "apng", "dicom",
            "jp2", "j2k", "tga", "webp", "tif", "gif", "ico" };
    List<string> vectorFormats = new List<string>() { "svg", "otg", "odg", "eps", "wmf", "emf", "wmz", "emz", "cmx", "cdr" };

    List<string> allFormats = new List<string>(rasterFormats);
    allFormats.AddRange(vectorFormats);

    allFormats.ForEach(
        formatExt =>
        {
            var inputFile = Path.Combine(templatesFolder, $"template.{formatExt}");
            bool isVectorFormat = vectorFormats.IndexOf(formatExt) > -1;

            //Need to rasterize vector formats before background remove
            if (isVectorFormat)
            {
                inputFile = RasterizeVectorImage(formatExt, inputFile);
            }

            var outputFile = Path.Combine(templatesFolder, $"{filterName}_{formatExt}.png");

            Console.WriteLine($"Processing {formatExt}");

            using (var image = (RasterImage)Image.Load(inputFile))
            {                        
                doFilter(image);

                //If image is multipage save each page to png to demonstrate results
                if (image is IMultipageImage multiPage && multiPage.PageCount > 1)
                {
                    for (var pageIndex = 0; pageIndex < multiPage.PageCount; pageIndex++)
                    {
                        string fileName = $"{filterName}_page{pageIndex}_{formatExt}.png";
                        multiPage.Pages[pageIndex].Save(templatesFolder + fileName, new PngOptions());
                        File.Delete(templatesFolder + fileName);
                    }
                }
                else
                {
                    image.Save(outputFile, new PngOptions());
                    File.Delete(outputFile);
                }
            }

            //Remove rasterized vector image
            if (isVectorFormat)
            {
                File.Delete(inputFile);
            }
        }
        );
}

string RasterizeVectorImage(string formatExt, string inputFile)
{
    string outputFile = Path.Combine(templatesFolder, $"rasterized.{formatExt}.png");
    using (var image = Image.Load(inputFile))
    {                
        image.Save(outputFile, new PngOptions());
    }

    return outputFile;
}