[iText-questions] Extracted images are upside-down

[John van de Pol]

Hi all,



I searched the iText mailinglist fort his problem.

I found several, but none of the provided solutions work for me.



I am making a program for a friend of mine wich must extract images from a
pdf.

All the images are upside down, they are NOT rotated!!



Here's the pdf:
www.jpproducties.nl/Documents/order 200047.pdf
<http://www.jpproducties.nl/Documents/order%20200047.pdf>



Here's the extracted image from the first page:

www.jpproducties.nl/Documents/test_1_0.png



Here's my codesnippet.

The class has 2 methods.

1 without _outputFilePrefix and _outputFolder, this one is the one i intend
to use.

The other method can be used to write the images to file.

Both methods give the images upside down.



public void RenderImage(ImageRenderInfo renderInfo)

{

try

{

PdfImageObject image = renderInfo.GetImage();

if (image != null)

{

if (_outputFilePrefix.Length == 0 ||
_outputFolder.Length == 0)

{

var drawingImage = image.GetDrawingImage();

_retList.Add(drawingImage);

}

else

{

var imageFileName = String.Format("{0}_{1}_{2}.{3}",
_outputFilePrefix, _currentPage, _imageCount, image.GetFileType());

var imagePath =
System.IO.Path.Combine(_outputFolder, imageFileName);

if (_overwriteExistingFiles ||
!File.Exists(imagePath))

{

var imageRawBytes = image.GetImageAsBytes();

File.WriteAllBytes(imagePath, imageRawBytes);

}

// Subtle: Always increment even if file is not
written. This ensures consistency should only some

// of a PDF file's images actually exist.

_imageCount++;

}

}

}

catch (Exception)

{

}

}



Thank in advance for your help.



Best Regards,

JohnvandePol

[mkl]

Post by John van de Pol
I am making a program for a friend of mine wich must extract images from a
pdf.
All the images are upside down, they are NOT rotated!!

The reason simply is that the images ARE upside-down in the page resources
and are then flipped back up by the transformation matrix active when the
image is drawn.

The image data you store are from the page resources, no transformations
applied. If you want to know if some extraordinary transformation is applied
to it afterwards, you also have to check the renderInfo.GetImageCTM - the
current transformation matrix at the time the image is drawn.

E.g. in your case the top image is drawn using the instructions

604.29 0 0 -851.16 0 839 cm
/I0 Do

I.e. it is stretched to 604.29 units horizontally and -851.16 units
vertically, and that negative value for the y coordinate implies mirroring
the image resource upside-down.

To get an image exactly as rendered, you have to apply the equivalent
transformation to the image data you have retrieved using image processing
code.

Regards, Michael



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