Detecting rotated/inverted images with PDFBox

Question

I've got some PDFs which have images that are rotated and inverted. Sample of the image:

The page object itself has no rotation instructions but it appears they may be using the cm operator in the content stream to perform the transformation for the rendered PDF:

...snip...
q
  0.05 0 0 -0.05 0 768 cm
  q
    0 0 11880 15360 re
    W*
    n
    /GS0 gs
    1 J
    [ ] 0 d
    2 w
    0 0 0 RG
    /GS0 gs
    1 1 1 rg
    /GS0 gs
    1 1 1 rg
    /GS0 gs
    1 J
    [ ] 0 d
    2 w
    0 0 0 RG
    q
      11865 0 0 15360 0 -3 cm
      /Image1 Do
    Q
...snip...    

Am I on the right track here?

We're already using PDFStreamEngine to analyze images so I thought maybe using the current graphics state would have these available:

protected class DrawObjectCounter extends OperatorProcessor {
   @Override
   public void process(Operator operator, List<COSBase> operands) throws IOException {
       System.out.println(getGraphicsState().getCurrentTransformationMatrix());
       ...snip...
   }
...snip...   

The output is always:

[1.0,0.0,0.0,1.0,0.0,0.0]

Do I need to keep track of the CM operators with another OperatorProcessor or am I just not looking in the right place?

Answer 1

I had a problem in the construction of my PDFStreamEngine. I needed to register operators to perform the matrix modifications:

public PdfImageStreamEngine() {
    // pdfbox operators
    addOperator(new Save());
    addOperator(new Concatenate());
    addOperator(new Restore());
    // custom operators
    addOperator(new DrawObjectCounter());
    addOperator(new BeginInlineImageCounter());
    addOperator(new LineToCounter());
}

Once I registered the proper operator processors, the getCurrentTransformationMatrix had the correct value.