Code snippet showing how to create an equirectangular cloud image from University of Wisconsin-Madison Space Science and Engineering Center web mercator tiles, see https://ithoughthecamewithyou.com/post/improving-the-accuracy-of-the-new-catfood-earth-clouds-layer for more information

clouds.cs

string cloudsDownloadPath = HostingEnvironment.MapPath(CloudsDownloadName);
string cloudsTransformedPath = HostingEnvironment.MapPath(CloudsTransformedName);
string cloudsWarpedPath = HostingEnvironment.MapPath(CloudsWarpedName);
string cloudsFinalPath = HostingEnvironment.MapPath(AxdCloudsHandler.CloudsPath);
string gdalFolder = HostingEnvironment.MapPath(GdalFolder);
string gdalTranslatePath = HostingEnvironment.MapPath(GdalTranslate);
string gdalWarpPath = HostingEnvironment.MapPath(GdalWarp);

// download the most recent tiles
using (Bitmap cloudImage = new Bitmap(CloudsTileDimension * CloudsTileCount, CloudsTileDimension * CloudsTileCount, PixelFormat.Format32bppArgb))
{
    using (Graphics g = Graphics.FromImage(cloudImage))
    {
        g.CompositingMode = CompositingMode.SourceCopy;
        g.CompositingQuality = CompositingQuality.HighQuality;
        g.InterpolationMode = InterpolationMode.HighQualityBicubic;
        g.SmoothingMode = SmoothingMode.HighQuality;
        g.PixelOffsetMode = PixelOffsetMode.HighQuality;

        using (WebClient webClient = new WebClient())
        {
            for (int col = 0; col < CloudsTileCount; col++)
            {
                for (int row = 0; row < CloudsTileCount; row++)
                {
                    using (Stream tileStream = webClient.OpenRead($"http://realearth.ssec.wisc.edu/products/globalir/4/{col}/{row}.png"))
                    {
                        // for future expansion, might be better to project onto a cylinder...
                        using (Bitmap tile = new Bitmap(tileStream))
                        {
                            int x = col * CloudsTileDimension;
                            int y = row * CloudsTileDimension;
                            g.DrawImage(tile, x, y);
                        }
                    }
                }
            }
        }
    }

    cloudImage.Save(cloudsDownloadPath, ImageFormat.Png);
}

// add dimensions to image
ProcessStartInfo psiTranslate = new ProcessStartInfo();
psiTranslate.Arguments = $"-a_srs EPSG:3857 -a_ullr -20037508 20037508 20037508 -20037508 -r lanczos {cloudsDownloadPath} {cloudsTransformedPath}";
psiTranslate.CreateNoWindow = true;
psiTranslate.UseShellExecute = false;
psiTranslate.FileName = gdalTranslatePath;
psiTranslate.LoadUserProfile = false;
psiTranslate.WorkingDirectory = gdalFolder;
Process pTranslate = Process.Start(psiTranslate);
pTranslate.WaitForExit();

// warp image
ProcessStartInfo psiWarp = new ProcessStartInfo();
psiWarp.Arguments = $"-s_srs EPSG:3857 -t_srs EPSG:4326 -r lanczos -wo SOURCE_EXTRA=1000 -overwrite -te -180 -88.99999 180 88.99999 -te_srs EPSG:4326 {cloudsTransformedPath} {cloudsWarpedPath}";
psiWarp.CreateNoWindow = true;
psiWarp.UseShellExecute = false;
psiWarp.FileName = gdalWarpPath;
psiWarp.LoadUserProfile = false;
psiWarp.WorkingDirectory = gdalFolder;
Process pWarp = Process.Start(psiWarp);
pWarp.WaitForExit();

// drop lighter pixels and flip
using (Image warped = Image.FromFile(cloudsWarpedPath))
{
    using (Bitmap final = new Bitmap(CloudsFinalWidth, CloudsFinalHeight, PixelFormat.Format32bppArgb))
    {
        using (Graphics g = Graphics.FromImage(final))
        {
            g.CompositingMode = CompositingMode.SourceCopy;
            g.CompositingQuality = CompositingQuality.HighQuality;
            g.InterpolationMode = InterpolationMode.HighQualityBicubic;
            g.SmoothingMode = SmoothingMode.HighQuality;
            g.PixelOffsetMode = PixelOffsetMode.HighQuality;

            g.FillRectangle(Brushes.Black, 0, 0, CloudsFinalWidth, CloudsFinalHeight);

            g.DrawImage(warped,
                new Rectangle(0, 0, CloudsFinalWidth, CloudsFinalHeight),
                0, 0, warped.Width, warped.Height,
                GraphicsUnit.Pixel);

            // need to fill in missing area at top and bottom
            FlipClouds(final, g, true);
            FlipClouds(final, g, false);
        }

        for (int x = 0; x < final.Width; x++)
        {
            for (int y = 0; y < final.Height; y++)
            {
                Color c = final.GetPixel(x, y);
                final.SetPixel(x, y, Color.FromArgb(
                        (int)Math.Max(c.R - ((255.0 - c.R) * CloudsPixelFactor), 0),
                        (int)Math.Max(c.G - ((255.0 - c.G) * CloudsPixelFactor), 0),
                        (int)Math.Max(c.B - ((255.0 - c.B) * CloudsPixelFactor), 0)
                    ));
            }
        }

        lock (AxdCloudsHandler.CloudsUpdateLock)
        {
            final.Save(cloudsFinalPath, ImageFormat.Jpeg);
        }
    }
}

// delete intermediate 
if (File.Exists(cloudsWarpedPath)) { File.Delete(cloudsWarpedPath); }
if (File.Exists(cloudsTransformedPath)) { File.Delete(cloudsTransformedPath); }
if (File.Exists(cloudsDownloadPath)) { File.Delete(cloudsDownloadPath); }