Knocking out 'grunge effect' to have transparency surrounging coloured image

[JMS86]

Hi all, I have a problem that I guess (and hope) will be an easy fix for those in the know.

I currently have a comicy coloured background and would like to knock out a grunge effect border around it so that when printed on any colour shirt the coloured effect is the edge, and there is no white border around the outside. At the moment this looks pretty odd on darker coloured shirts as the white border stands out too much.

I primarily use indesign and was hoping to be able to simply drag and drop the grunge effect into indesign to knock out from the main image, but it converts it to an eps because of the amount of detail. I also tried importing the green and yellow background into Illustrator and knocking out using the pathfinder tool in but have not had any luck.

Am I doing something wrong and trying to overcomplicate it or am I simply asking too much? I could call it into Photoshop but I much prefer using the vector designs as they are sharper.

Any help is appreciated.

TL;DR: I want to make the white part of the attached transparent.

[Monika Gause]

You could check out opacity masks.

In Window > Transparency

This is the Illustrator forum, so you want to do this in Illustrator, not InDesign, right?

[Jacob Bugge]

JMS,

In addition to what Monika said, you may wish to soften the transition to the shirt colour by using a smooth (or many step) Blend for the opacity mask between a black outer path that encompasses the whole artwork/grunge effect and a white inner path at the boundary of the area where you wish to have the full grunge effect; such a B/W Blend will make the artwork/grunge effect fade into nothing outwards. This works with both Clip and Invert Mask unticked.