EyeonTips:Manual/Fusion 6/pImageEmitter

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Want more particles per pixel, but want more control over the interpolated values? Leave the Density at 1.0, but put a Scale after the input image. You can then control the density as well as set the filter type. --Chad 14:14, 18 November 2009 (EST)

pImageEmitter's Center

The number of particles depends on the input image's size. To emit a grid with a fixed number of particles in each axis, you need to calculate the X and Y density like this:

XDensity = [desired number of columns] / [image width]
YDensity = [desired number of rows] / [image height]

If the distance between each particle should instead be equal (e.g. aligned in squares), use the same number for both X and Y density.

In both cases, you will notice that the grid isn't centered properly around the emitter's center. There's always one row and one column missing. If you need the plane centered (for example exactly in front of the camera) you can modify the pivot values on the first tab (not on the transform tab) to half the distance between each row or column:

Pivot.X = 1 / (2 * [number of columns])
Pivot.Y = 1 / (2 * [number of rows]) / [image aspect]

(If you have used the same value for X and Y density, you also have to use the same value for X and Y pivot).

This screenshot demonstrates the calculations you need to perform. It doesn't have to be expressions, but they demonstrate the formulas better than the final numbers.