For data passes we make use of LPE modifiers, nothruput;noinfinitecheck;noclamp;unoccluded; you can find these at the bottom of the LPE page, for the purposes of this document you should pay most attention to the part of the LPE that begins with the camera (C) as it is used to define the path collected. The rest is included for completeness.

• unoccluded – returns unoccluded or unshadowed result. If not included, your result will include shadowing and may not be useful as a matte as the shape of the object and shadowing will be evident
• noclamp – returns unclamped result.
• nothruput – does not apply thruput (thruput is the accumulative albedo of the objects hit by rays). If omitted, the masks will be attenuated. For example, a color of 1,0,0 is pure red but may be 0.5,0,0 after a reflection or refraction, the actual result is based on the light path and material response(s)
• overwrite – instead of outputting the accumulated result, overwrite it. One example of using this is for the albedo output where we do not want an accumulated result. If left out your result may contain values different than expected. In this example the color 1,0,0 may return 6,0,0 etc. and bleed onto neighboring pixels
• noinfinitecheck – do not do any infinite check.

lpe:nothruput;noinfinitecheck;noclamp;unoccluded;overwrite;CU4L