Change colors of black-and-white TIFF after converting from PDF

In this article, we will demonstrate how to change the color palette after converting a PDF document to 1bpp TIFF in C#.

In the following code sample, we render a PDF to a 1bpp TIFF. Then create a bitmap from the TIFF, create a new color palette, edit the entries of this palette and assign this new palette to the bitmap.

static void Main(string[] args)
{
    Document document = new Document(new FileStream(@"..\..\input.pdf", FileMode.Open));

    // Convert the PDF Document to TIFF file
    ConvertToTiffOptions tiffOptions = new ConvertToTiffOptions(300.0, TiffCompression.CcittG3);

    string tempPath = @"..\..\tmp.tiff";
    using (FileStream drawImage = new FileStream(tempPath,
        FileMode.OpenOrCreate, FileAccess.Write))
    {
        document.Pages[0].ConvertToTiff(drawImage, tiffOptions);
    }

    string tiffPath = @"..\..\newImage.bmp";
    using (Bitmap tiff = new Bitmap(tempPath))
    {
        // Create a new colorpalette
        System.Drawing.Imaging.ColorPalette palette = Create1bbPalette();

        // Set the palette to other colors
        palette.Entries[0] = System.Drawing.Color.FromArgb(0, 0, 64, 128);
        palette.Entries[1] = System.Drawing.Color.FromArgb(0, 223, 233, 245);

        // Set the palette of the bitmap to the new palette 
        // Palette entries must be changed before assign the palette to the bitmap
        tiff.Palette = palette;

        // Save the new image with the new colorpalette
        tiff.Save(tiffPath, System.Drawing.Imaging.ImageFormat.Bmp);
    }

    File.Delete(tempPath);
}

static protected System.Drawing.Imaging.ColorPalette Create1bbPalette()
{
    Bitmap bitmap =
        new Bitmap(1, 1, System.Drawing.Imaging.PixelFormat.Format1bppIndexed);
    System.Drawing.Imaging.ColorPalette palette = bitmap.Palette;
    bitmap.Dispose();
    return palette;
}