private static bool optimizeImage(PdfPaintedImage painted, PdfDocument pdf)
{
PdfImage image = painted.Image;
// inline images can not be recompressed unless you move them to resources
// using PdfCanvas.MoveInlineImagesToResources
if (image.IsInline)
{
return(false);
}
// mask images are not good candidates for recompression
if (image.IsMask || image.Width < 8 || image.Height < 8)
{
return(false);
}
// get size of the painted image
int width = Math.Max(1, (int)painted.Bounds.Width);
int height = Math.Max(1, (int)painted.Bounds.Height);
if (width >= image.Width || height >= image.Height)
{
if (image.HasMask)
{
return(false);
}
if (image.ComponentCount == 1 && image.BitsPerComponent == 1 &&
image.Compression != PdfImageCompression.Group4Fax)
{
image.RecompressWithGroup4Fax();
}
else if (image.BitsPerComponent == 8 &&
image.ComponentCount >= 3 &&
image.Compression != PdfImageCompression.Jpeg &&
image.Compression != PdfImageCompression.Jpeg2000)
{
image.RecompressWithJpeg2000(10);
// or image.RecompressWithJpeg();
}
return(true);
}
// try to replace large masked images
if (image.HasMask)
{
if (image.Width < 300 || image.Height < 300)
{
return(false);
}
using (var stream = new MemoryStream())
{
PdfPage tempPage = pdf.AddPage();
tempPage.Canvas.DrawImage(image, 0, 0, width, height, 0);
PdfPaintedImage tempPaintedImage = tempPage.GetPaintedImages()[0];
tempPaintedImage.SaveAsPainted(stream);
pdf.RemovePage(pdf.PageCount - 1);
image.ReplaceWith(stream);
return(true);
}
}
if (image.Compression == PdfImageCompression.Group4Fax ||
image.Compression == PdfImageCompression.Group3Fax)
{
// Fax documents usually looks better if integer-ratio scaling is used
// Fractional-ratio scaling introduces more artifacts
int ratio = Math.Min(image.Width / width, image.Height / height);
// decrease the ratio when it is too high
if (ratio > 6)
{
ratio -= 5;
}
else if (ratio > 3)
{
ratio -= 2;
}
image.ResizeTo(image.Width / ratio, image.Height / ratio, PdfImageCompression.Group4Fax);
}
else if (image.ComponentCount >= 3 && image.BitsPerComponent == 8)
{
image.ResizeTo(width, height, PdfImageCompression.Jpeg, 90);
}
else
{
image.ResizeTo(width, height, PdfImageCompression.Flate, 9);
}
return(true);
}