PDFsharp & MigraDoc Foundation

Hi,

I am trying to compress PDF files using PDF sharp 1.5.

I am able to find both DCTDecode and FlateCode. As per my understanding these are JPG/JPEG and PNG streams respectively. I am able to compress DCTDecode images. But I am unable to compress FlateDecode streams.

I tried 2 Approaches to compress FlateDecode. 1) Use FlateDecode compression c# code 2) Replace FlateDecode with DTCDecode
In approach 1 I am getting the compressed PDF generated but the PNG image is getting distorted
In approach 2, I am getting the PDF corrupted

Interestingly I am able to successfully extract both types of images from PDF's

Please find both functions pasted below. It will be great if any experts can point out the mistake I am doing here.

==========================================================
Approach 1 Compression
==========================================================
private static void CompressPngImage(ref PdfDictionary image, ref int count)
{
int width = image.Elements.GetInteger(PdfImage.Keys.Width);
int height = image.Elements.GetInteger(PdfImage.Keys.Height);

var canUnfilter = image.Stream.TryUnfilter();
byte[] decodedBytes;

if (canUnfilter)
{
decodedBytes = image.Stream.Value;
}
else
{
PdfSharp.Pdf.Filters.FlateDecode flate = new PdfSharp.Pdf.Filters.FlateDecode();
decodedBytes = flate.Decode(image.Stream.Value);
}

int bitsPerComponent = 0;
while (decodedBytes.Length - ((width * height) * bitsPerComponent / != 0)
{
bitsPerComponent++;
}

System.Drawing.Imaging.PixelFormat pixelFormat;
switch (bitsPerComponent)
{
case 1:
pixelFormat = System.Drawing.Imaging.PixelFormat.Format1bppIndexed;
break;
case 8:
pixelFormat = System.Drawing.Imaging.PixelFormat.Format8bppIndexed;
break;
case 16:
pixelFormat = System.Drawing.Imaging.PixelFormat.Format16bppArgb1555;
break;
case 24:
pixelFormat = System.Drawing.Imaging.PixelFormat.Format24bppRgb;
break;
case 32:
pixelFormat = System.Drawing.Imaging.PixelFormat.Format32bppArgb;
break;
case 64:
pixelFormat = System.Drawing.Imaging.PixelFormat.Format64bppArgb;
break;
default:
throw new Exception("Unknown pixel format " + bitsPerComponent);
}

decodedBytes = decodedBytes.Reverse().ToArray();

Bitmap bmp = new Bitmap(width, height, pixelFormat);
BitmapData bmpData = bmp.LockBits(new Rectangle(0, 0, bmp.Width, bmp.Height), ImageLockMode.WriteOnly, bmp.PixelFormat);
int length = (int)Math.Ceiling(width * (bitsPerComponent / 8.0));
for (int i = 0; i < height; i++)
{
int offset = i * length;
int scanOffset = i * bmpData.Stride;
Marshal.Copy(decodedBytes, offset, new IntPtr(bmpData.Scan0.ToInt64() + scanOffset), length);
}
bmp.UnlockBits(bmpData);
bmp.RotateFlip(RotateFlipType.Rotate180FlipNone);
var TempPNGStream1 = new MemoryStream();

var TempPNGStream = new MemoryStream();

bmp.Save(TempPNGStream, ImageFormat.Png);

byte[] ImageBytes = ImageMagic.QualityEncode(TempPNGStream, ImageFormat.Png).ToArray();

ImageBytes=ImageMagic.QualityEncode(TempPNGStream, ImageFormat.Png).ToArray();
TempPNGStream.Write(ImageBytes, 0, ImageBytes.Length);

Bitmap bmp1 = new Bitmap(TempPNGStream);

BitmapData bmpData1 = bmp1.LockBits(new Rectangle(0, 0, width, height), ImageLockMode.WriteOnly, bmp1.PixelFormat);

byte[] data = new byte[Math.Abs(bmpData.Stride * bmpData.Height)];//applied bmpData instead of bmpData1
Marshal.Copy(bmpData1.Scan0, data, 0, data.Length);

decodedBytes = data;//.Reverse().ToArray();

PdfSharp.Pdf.Filters.FlateDecode flate1 = new PdfSharp.Pdf.Filters.FlateDecode();

image.Stream.Value = decodedBytes;// flate1.Decode(decodedBytes);

TempPNGStream1.Write(decodedBytes, 0, decodedBytes.Length);

bmp.Save(TempPNGStream1, ImageFormat.Jpeg);
bmp.Save("D:\\CustomCompression\\Uploaded through API\\RE9fQURfMTU2Nl8yNDRfMjAwMQ==/"+String.Format("Image{0}.png", count++), System.Drawing.Imaging.ImageFormat.Png);

 }

===========================================================================
Approach 2 Replace FlateDecode with DCTDecode
===========================================================================
private static void ReplacePngImageDictionaryWithJpg(ref PdfDictionary image, ref int count)
{
int width = image.Elements.GetInteger(PdfImage.Keys.Width);
int height = image.Elements.GetInteger(PdfImage.Keys.Height);

var canUnfilter = image.Stream.TryUnfilter();
byte[] decodedBytes;

if (canUnfilter)
{
decodedBytes = image.Stream.Value;
}
else
{
PdfSharp.Pdf.Filters.FlateDecode flate = new PdfSharp.Pdf.Filters.FlateDecode();
decodedBytes = flate.Decode(image.Stream.Value);
}

int bitsPerComponent = 0;
while (decodedBytes.Length - ((width * height) * bitsPerComponent / != 0)
{
bitsPerComponent++;
}

System.Drawing.Imaging.PixelFormat pixelFormat;
switch (bitsPerComponent)
{
case 1:
pixelFormat = System.Drawing.Imaging.PixelFormat.Format1bppIndexed;
break;
case 8:
pixelFormat = System.Drawing.Imaging.PixelFormat.Format8bppIndexed;
break;
case 16:
pixelFormat = System.Drawing.Imaging.PixelFormat.Format16bppArgb1555;
break;
case 24:
pixelFormat = System.Drawing.Imaging.PixelFormat.Format24bppRgb;
break;
case 32:
pixelFormat = System.Drawing.Imaging.PixelFormat.Format32bppArgb;
break;
case 64:
pixelFormat = System.Drawing.Imaging.PixelFormat.Format64bppArgb;
break;
default:
throw new Exception("Unknown pixel format " + bitsPerComponent);
}

decodedBytes = decodedBytes.Reverse().ToArray();

Bitmap bmp = new Bitmap(width, height, pixelFormat);
BitmapData bmpData = bmp.LockBits(new Rectangle(0, 0, bmp.Width, bmp.Height), ImageLockMode.WriteOnly, bmp.PixelFormat);
int length = (int)Math.Ceiling(width * (bitsPerComponent / 8.0));
for (int i = 0; i < height; i++)
{
int offset = i * length;
int scanOffset = i * bmpData.Stride;
Marshal.Copy(decodedBytes, offset, new IntPtr(bmpData.Scan0.ToInt64() + scanOffset), length);
}
bmp.UnlockBits(bmpData);
bmp.RotateFlip(RotateFlipType.Rotate180FlipNone);
var TempPNGStream1 = new MemoryStream();

var TempPNGStream = new MemoryStream();

bmp.Save("D:\\CustomCompression\\Uploaded through API\\RE9fQURfMTU2Nl8yNDRfMjAwMQ==/" + String.Format("Image{0}.png", count++), System.Drawing.Imaging.ImageFormat.Png);

bmp.Save("D:\\CustomCompression\\Uploaded through API\\RE9fQURfMTU2Nl8yNDRfMjAwMQ==/" + String.Format("Image{0}.jpg", count++), System.Drawing.Imaging.ImageFormat.Jpeg);

bmp.Save(TempPNGStream, ImageFormat.Jpeg);

string CurrentColorSpace = image.Elements.GetName("/ColorSpace");

image.Stream.Value = TempPNGStream.ToArray().ToArray();
image.Elements.SetValue("/Height", new PdfInteger(bmp.Height));
image.Elements.SetValue("/Width", new PdfInteger(bmp.Width));
image.Elements.SetValue("/Length", new PdfInteger(image.Stream.Value.Length));
image.Elements.SetValue("/ColorSpace", new PdfString(CurrentColorSpace));
image.Elements.SetValue("/Filter", new PdfString("/DCTDecode"));
image.Elements.SetValue("/Type", new PdfString("/XObject"));
image.Elements.SetValue("/Name", new PdfString("/Im0")); //new PdfString(String.Format("Image{0}.jpg", count++)));
image.Elements.Remove("/Interpolate");
image.Elements.Remove("/DecodeParams");

}

Thanks
Praveen

Hi!

You don't waste much time writing comments in your source code.
PDF files do not contain PNG images, they contain PDF images or JPEG images.
I'm afraid you cannot simply use the PNG encoder to get PDF images.

With JPEG images, make sure the properties of the image are set correctly.

_________________
Best regards
Thomas
(Freelance Software Developer with several years of MigraDoc/PDFsharp experience)

Thanks for the response.
With PNG, I mean FlateDeCode images, may be your approach is the correct one. JPEG images are perfectly getting compressed and PDF size is getting reduced. But when I try to compress and replace FlateDeCode images, (which I am able to extract and save locally as images) images in PDF are getting skewed or PDF itself is getting corrupted.

Thank you
Praveen
Praveen

Image rows in Windows BMP files are DWORD-aligned, but image rows in PDF format are BYTE-aligned. This may account for the skewing.

When adding images, you must reverse the extraction process exactly. Looks as if there are issues with your code adding the new images in PDF format.

_________________
Best regards
Thomas
(Freelance Software Developer with several years of MigraDoc/PDFsharp experience)

Thanks for the response. Let me check it and update.