Black background in raster image becomes dark gray

[aella]

I'm importing raster images (high resolution tiff images) with a black background in Illustrator. The import was done with the Place command.

Everything looks fine on screen, but once I print the document, the background ends up dark gray instead of pure black in all the images except one. It's not a printer problem, since I get the same thing when creating a pdf file.

I've checked that the background is really black in my original images (yup, RGB (0,0,0) CYMK (0,0,0,100%) all the way)

Any idea what causes this, or tips for a work-around?

 

[aella]

Oups, wrong... The RGB is indeed 0,0,0, but Photoshop converts that to (53,62,51,100%) CMYK no matter what values I use. But the good image (the one that prints ok) and the others have exactly the same color.