PDFlib Text Extraction Toolkit (TET) Manual

7.4 Restrictions and Caveats
Image color fidelity. TET does not degrade image quality when extracting images:
> Raster images are never downsampled.
> The color space of an image will be retained in the output. TET never applies any
CMYK-to-RGB or similar color conversion.
> The number of color components will always be unchanged. For example, RGB images
will not be changed to grayscale if they contain only gray colors.
Image workarounds. In some situations the color appearance of the extracted image
may be different from the visual appearance of the PDF page. While the image shape is
preserved, the colors may appear different because of the following reasons:
> Image masks are be applied.
> Colorized grayscale images are extracted without the color, but as grayscale images.
> Since DeviceN color is not supported in TIFF, images with the DeviceN colorspace are
extracted as grayscale, RGB, or CMYK images for N=1, 3, and 4, respectively. For N>4
CMYK TIFF images with one or more alpha channels are generated.
> Images with Separation colorspace are extracted as grayscale images. The spot color
used to colorize the image will be lost.
> Images with Indexed ICCBased colorspace: the ICC profile will be ignored.
Unexpected results when extracting images. In some cases the shape of extracted images
may appear different from the PDF page:
> Images may appear mirrored horizontally (upside down) or vertically. This is caused
by the fact that TET extracts the original pixel data of the image, without respect to
any transformation which may have been applied to the image on the PDF page.
> Since image masks are ignored, masking effects will not be reflected in the extracted
image.
Unsupported image types. The following types of PDF images can not be extracted, i.e.
TET_write_image_file( ) will return -1 in these cases:
> PDF inline images
> Images with JBIG2 compression
> Images with Indexed Lab colorspace.
7.4 Restrictions and Caveats 87