PDFlib Text Extraction Toolkit (TET) Manual

7.2 Image Geometry
Using TET_get_image_info( ) you can retrieve geometric information for a placed image.
The following values are available for each image in the TET_image_info structure (see
Figure 7.1):
> The x and y fields are the coordinates of the image reference point. The reference
point is usually the lower left corner of the image. However, coordinate system
transformations on the page may result in a different reference point. For example,
the image may be mirrored horizontally with the result that the reference point becomes
the upper left corner of the image.
> The width and height fields correspond to the physical dimensions of the placed image
on the page. They are provided in points (i.e. 1/72 inch).
> The angle alpha describes the direction of the pixel rows. This angle will be in the
range -180˚ < alpha ³ +180˚. The angle alpha rotates the image at its reference point.
For upright images alpha will be 0˚.
> The angle beta describes the direction of the pixel columns, relative to the perpendicular
of alpha. This angle will be in the range -180˚ < beta ³ +180˚, but different
from • 90˚. The angle beta skews the image, and beta=180˚ mirrors the image at the x
axis. For upright images beta will be in the range -90˚ < beta < +90˚. If abs(beta) >90˚
the image is mirrored at the baseline.
> The imageid field contains the pCOS ID of the image. It can be used to retrieve detailed
image information with pCOS functions and the actual image pixel data with
TET_write_image_file( ) or TET_get_image_data( ).
As a result of image transformations, the orientation of the extracted images may appear
wrong since the extracted image data is based on the image object in the PDF. Any
rotation or mirror transformations applied to the placed image on the PDF page will not
be applied to the pixel data, but the original pixel data will be extracted.
Image resolution. In order to calculate the image resolution in dpi (dots per inch) you
must divide the image width in pixels by the image width in points and multiply by 72:
while (tet.get_image_info(page) == 1) {
String imagePath = "images[" + tet.imageid + "]";
int width = (int) tet.pcos_get_number(doc, imagePath + "/Width");
int height = (int) tet.pcos_get_number(doc, imagePath + "/Height");
double xDpi = 72 * width / tet.width;
height
Fig. 7.1
Image geometry
(x, y)
alpha
width
7.2 Image Geometry 83