CCITT-Images with colorspace different from PDIndexed are created using PDCCitt.java/getRGBImage:
The value Transparency.OPAQUE (=1) is provided for the parameter "transparentIndex" - this creates an image, in which the white color is treated as transparent.
This bug is especially annoying for some OCR-documents I had to work with (using PageDrawer). They consist of rendered text (as result of the OCR), that has the original content as image rendered on top, fully covering the text. When the white background is rendered as transparent, the rendered page gets messed up, because both texts can be seen,
Replace the value Transparency.OPAQUE with -1, so that no color is transparent.