Rendering FAQ

Maxwell Emitters behave according to real-world parameters. Therefore, it is necessary to:

• First of all, check the scale of your scene (which you can do by importing your MXS file into Maxwell Studio). As Maxwell Render is a light simulator, scene scale is very important - you cannot illuminate a 2 km2 area with a 60 Watt light bulb.
• Check the normals of your emitter objects. You can try reversing them with the "Reverse" normals button in the Object Parameters panel, and then rendering again.
• Check your camera settings, particularly the f-Stop, Shutter speed and ISO parameters. If there is not enough light coming into the camera, the image will be black.
• Make sure that the Emitter power is defined correctly. (Don't forget efficacy for watt-based emitters.

There are several things you can do to optimize a scene, mostly related to emitters:

• Make sure your emitting surfaces are as low-poly as possible. Usually, a single-sided polygon will be sufficient.
• If possible, do not completely enclose your emitters inside a dielectric object.
• Make sure your emitter is not intersecting other geometry.
• Very important: do not include very white or fully saturated materials in your scene. For example, a completely white (255, 255, 255) material will take a very long time to clear and will also make the contrast in the image disappear. Also avoid completely saturated colors such as pure red (255, 0, 0). Pure white or pure saturated materials do not exist in real life so it's better to decrease the saturation a bit. For a white wall, around RGB 220 or less is sufficient.
• For interior renders where window glass reflections are necessary, use the Architectural Glass Solution (AGS) for the windows instead of real glass. This will create the reflections but will not produce any caustics, thus speeding up the rendering. - Perhaps you simply need more time for rendering, depending on your machine specs. 

You can use the Pack & Go feature found in most of the plugins and also from Maxwell Studio. In Studio, open your MXS file (Maxwell scene file). Go to File>Pack & Go and choose an output folder. Studio will copy the MXS file and any other files needed to render the scene (textures, IOR, IES, HDR files etc) to the folder. You can then just copy this folder to another computer and render. The paths to the textures specified in the MXS file will still point to paths relevant to the old computer, but because with Pack & Go the textures are copied to the same folder where the MXS file is, Maxwell will also look in this folder when searching for textures so the render will start normally.

This is related to the camera sensor aspect ratio, that surely differs from the render aspect ratio.

As a real camera, Maxwell needs both aspect ratios to be equal. Check the section about Camera Sensor size and Render resolution in this page for a further explanation.

That's a very deep topic that depends on many factors. The most important factors are the required viewing distance and the printing device specifications (dots per inch). Of course the final resolution must fulfill your printing device specifications, that obviously vary from billboard to magazine print.
But keep in mind that rendering larger does not always equate to display more details, since you bake the maximum amount of detail already into the scene when you modeled and textured it. Unlike reality, where you will see increasingly more detail the closer you get, a 3D scene will in fact get worse and worse after a certain point. In case you have no other indication, you can remind that the majority of renderings used in billboards archviz projects are around 4k to 6k pixels. Higher than that, an hypothetic 15k render would not show more detail (due the modeling and texturing limitation mentioned above) while the rendering process and memory needed would even not be affordable.

There are of course some situations, mainly on visualization of hard surface objects like technical pieces or jewelry, that could eventually benefit from rendering larger than 4k-6k since they consists on an accurate rendition of edges and corners, and other media that demand more resolution than billboards.