Dave Wortley has shared Camera Map Ratio, a handy 3ds Max script that customizes Camera Map projections (including CameraMapPerPixel) with different aspect ratios. With this script, you’ll no longer need other plugins or shaders.
This tool uses camera scaling to compensate for the difference between the aspect ratio of the render and that of the projected texture.
“By default in standard 3dsmax the Camera Map Modifier has a projection aspect ratio the same as the camera/render resolution, this isn’t good if you need to project a portrait image on a landscape render. Whilst there are plugins/MCG/OSL solutions to this, my solution works on standard max, with no plugins needed to reload the scene. It even works on CameraMapPerPixel too,” writes Worthley in the script details.
The developer claims that the script can automatically detect a texture on an object from which the camera map is projected with the same channel ID. All users need to do is select a camera. If they need to change the render’s aspect ratio, it may be done by restarting the script to restore the projections.