I need help - I can help - How can i know if an image is drawn rotated

Print Page | Close Window

How can i know if an image is drawn rotated

Printed From: Debenu Quick PDF Library - PDF SDK Community Forum
Category: For Users of the Library
Forum Name: I need help - I can help
Forum Description: Problems and solutions while programming with the Debenu Quick PDF Library and Debenu PDF Viewer SDK
URL: http://www.quickpdf.org/forum/forum_posts.asp?TID=2010
Printed Date: 06 May 25 at 11:32AM
Software Version: Web Wiz Forums 11.01 - http://www.webwizforums.com

Topic: How can i know if an image is drawn rotated

Posted By: bart_bender
Subject: How can i know if an image is drawn rotated
Date Posted: 25 Oct 11 at 11:06AM

Hello.

I'm trying duplicate a PDF image with a OCR layer.
When extract the image from the document, this is rotated 90º (i see this in the width and height properties)

How can i know if an image is drawn rotated in the original file for to use the FitImage method with rotation property?

Thanks in advance
Best Regards

Replies:

Posted By: Ingo
Date Posted: 25 Oct 11 at 8:52PM

Hi Bart!

QuickPDF offers functions to set these properties but not to get these values.
You can do it by your own.
Read the real content of your pdf-document into a stream and search for "rotate".
In my sample i've found the following pdf-code:
<<
/Type /Page
/Parent 5 0 R
/MediaBox [0 0 592.3 839]
/Resources <<
/Font <<
/F1 6 0 R /F2 7 0 R /F3 8 0 R >>
/XObject <<
/I1 9 0 R /I2 10 0 R /I3 11 0 R /I4 12 0 R /I5 13 0 R >>
/ProcSet 2 0 R >>
/Contents 3 0 R
/Rotate 90
>>
endobj
9 0 obj <<

... a 90 degrees rotation ;-)
The direct pdf-content is readable.
Try to open a pdf with Notepad and search for "rotate".
Normally you'll find a "/Rotate 0" ...

Cheers, Ingo

Posted By: AndrewC
Date Posted: 26 Oct 11 at 3:09AM

QP.PageRotation() returns the current orientation for the currently selected page.

Andrew.

Posted By: nothin
Date Posted: 07 Mar 12 at 11:21PM

Andrew,

Can you give an example of how you would use the PageRotation() function in a PDF file?

Can this be used in an FDF file? Can it be used to find what the page rotation is in whatever document the FDF file is imported into?

Thanks.

Posted By: Ingo
Date Posted: 07 Mar 12 at 11:29PM

Hi Nothin!

You can try any sample here or from the official support pages.

After LoadFromFile you should try PageCount and then a loop

with SelectPage.

Inside the loop you can use PageRotation.

No, you can't use it with FDF.

Cheers and welcome here,

Ingo

Posted By: edvoigt
Date Posted: 10 Mar 12 at 3:25PM

Hi,

You have to distinguish two kinds of rotation.

First is the rotation of a page. It takes the full content of a page. To determine it, there is PageRotation in QPL. It's result is what you find inside the "headdata" of an page-object in a PDF. But it is no solution for you.

How much an image is rotated is a fully other question. At now for this there is no QPL-function to get the needed info.

So we build our own PDF with a rotated image in it.

QP.SetMeasurementUnits(1); // unit mm
QP.SetPageDimensions(210, 297); // A4
QP.SetOrigin(0); // Bottomleft
QP.AddImageFromFile('blueFolder.bmp', 0);
QP.DrawRotatedImage(105,105, 100,50, 90); // rotate around the pagecenter 90°
QP.SaveToFile('rotatedimage.pdf');

Now we look inside:
There are some objects inside. We are interested only in
obj 2 - the page object, consisting at most of
obj 7 - our image under the name /QuickPDFImb9288b05
obj 5 - the PDF-operations, which build the pagecontent

So we see in obj 5
q
0 1 -1 0 297.6378 297.6378 cm
283.4646 0 0 141.7323 0 0 cm
/QuickPDFImb9288b05 Do
Q

The answer to your question is inside the both cm-operators. They contain data to be concatenated with transformation matrix and are the key. In the PDF-Specs (chapter 4.2.3) from Adobe you find a explanation of this matrix. From this you may find who describes a rotation. This may only such cm's are, where the first four values are of the kind c s -s c. That's because they are sinus und cosinus-values of an angle which is used for clounterclockwise rotation. There we find a sinus of 1.0 (90°) and its cosinus with 0.

But it is a little bit more difficult, because in one operation is more than only rotation possible. In one matrix may be rotation, scaling, skewing and translation. So it depends on the producer of the PDF, how he constructs his cm-operators and how difficult to get the angle-info back.

At the end you have to mix your knowledge about the angle under which the image is drawn and a possible pagerotation, which may be important too.

Cheers,
Werner