Particle Playground: trouble with wall and particle image

Question

Hello Friends,
I'm fairly new to all of the fancy stuff in After Effects, particularly particles, but I've had a lot of success so far, and just one problem that I can't seem to figure out. Perhaps someone here can help me.
I'm trying to create a clip of a cartoon bride and groom being pelted by rice. I've got the image of the cartoon bride and groom, and it looks great. I then created a new solid layer and applied the Particle Playground effect, and positioned the cannon so the particles come in from offscreen (around the 10 o'clock position). I tried creating masks on the side of the bride and groom's heads (drawn with the pen tool) for the rice to bounce off of, and that part seemed to work, too. At this point, I have the default red squares as particles, and they're bouncing off of the masks just like I want them to, but they don't look anything like rice. I change the color to white, and it looks a lot better, but still not as much like rice as I'd like.
Now, I figure out how to use a layer map to create particles from an image. I use a new shape layer and use the shape tools to create a single grain of rice (a white elongated ellipse with a black stroke). I then set the layer map controls to my rice grain layer, and adjust the scale properties of the rice grain until I have particles that look perfect. Hundreds of grains of rice, all the right size and shape, and they all look great but they're all oriented in the same direction, so I've got to make them move in a more random way. My next step is to animate the rice grain layer to rotate three times in one direction, then back three rotations over the course of three seconds. I then set the parameters to create the particles from a random starting point in the three-second layer. Success! The rice looks like rice! It's the right size, shape, and rotates with the right degree of randomness!
But the boundary mask isn't working anymore. The cannon is shooting the rice particles everywhere but where the mask is, so I get none of the desired bounce and interaction. There's an empty swath where no particles are being generated, so there are particles above and below the wall mask, but none moving directly toward it as I want. It's as if the mask is keeping the cannon from creating particles.
I tried moving the mask away from it's original position, and it affects the creation of the particles, but not in a way that makes sense to me. I tried decreasing the diameter of the cannon, and it behaves almost as if the mask is right next to the cannon, not where it appears in the comp.
Does anyone have any ideas about this? It seems like I'm really close...

Answer 1

Technically, in a proper Image Sequence, all images are the same size/aspect ratio.
What you'll need to do is make on set (vertical or horizontal) a new size, to fit inside the other. The Particle Emitter will matte it's images to one or the other, which ever comes first.