Browsing PDF page content. Problem with color spac

问题:

I am writing a program that would validate PDF file. I am using iText java library to get content of a file, but I have some problems with parsing it. I need to get info about color space and DPI of each image. How can I get info about position and dimensions of image in PDF? I tried to browse each XObject of PDF but I stuck, I cannot find any information about width and height of file in PDF. Are there any other libraries which can help me? Thank You for all answers and tips.

回答1:

The image object in the PDF file stores only the Width and the Height of the image in pixels. In order to know the position and size of the image on the page, in PDF points, you have to execute the page content stream, to create a virtual rendering. The image is painted on the page using the 'Do' operator and its position and size are given by the current transformation matrix that is in place when the 'Do' operator is executed.
The DPI for a specific drawing instance is computed as 72*imageSizeInPixels/imageSizeInPoints, imageSizeInPoints being computed as described above.