1. Here's why

Lumion 8.3 and newer: You do not need to read this article as it does not apply to newer versions of Lumion.

Lumion 8.0 and older: The MaterialID output image is rendered at a lower resolution on Print and Poster renderings in Lumion 8.0 and older versions.

This is due to a technical constraint as Print and Poster images are rendered in a different way in older versions of Lumion.

2. Workaround

2.1: If MaterialID output images in Print or Poster resolution are important in your project and you are using Lumion 8.0, we recommend rendering the MaterialID output image in Ultra HD (3840x2160) output resolution via the Image sequence tab.

This is the same resolution as Print resolution in Photo Mode. Please note that the Ultra HD output resolution requires a graphics card with 6GB memory (or more).

Render Clip (or Render Movie) -> Image Sequence tab -> Frame Range -> Range

2.2: If MaterialID output images are vital for editing a Poster resolution image in your project and you can't upgrade to Lumion 8.3 or newer, consider enlarging the Ultra HD MaterialID output image:

Knowledge Base: How do you render images at a higher resolution than Poster renderings?