The following are recommendations on obtaining the best performance from physical target images. Image Targets should be rigid, not flexible, with matte surface, but no gloss. Small targets are good for user manipulation. Be creative when choosing targets; make them appropriate, relevant, and fun.
A hard material such as card stock, plastic, or paper fixed to a non-flexible surface is better than a simple printed piece of paper. The reason is that the flexibility of the printed piece of paper can make it difficult for the object to stay in focus. However, paper targets are easily reproducible and widely available, so do not completely discount them as valid targets.
Be aware that even if you provide detailed instructions for the printing size and the paper quality, most users will revert to the default of their printer, which is usually A4 or US letter. To avoid these printing problems, you should provide targets that are books, marketing materials, packaging, or posters.
For tabletop, near-field, product shelf, and similar scenarios, a physical printed Image Target should be at least 5 inches, or 12 centimeters, in width and of reasonable height for a good AR experience. The recommended size varies based on the actual target rating and the distance to the physical Image Target.
In general, the larger the distance between the camera and the target, the bigger your target should be. As an estimate, consider that a 20-30 cm wide target should be detectable up to about 2-3 meters distance, which is about 10 times the target size. However, be aware that this value is an empirical indication and the actual size/distance ratio may vary significantly based on other factors.
The quality of the tracking that uses the Vuforia Engine can degrade significantly when the printed targets are not flat. When designing the physical printouts, game boards, play pieces, etc, ensure that the targets do not bend, coil up, and are not creased or wrinkled. A simple trick is to use thick paper when printing, for example, 200-220 g/m². A more elegant solution is to get the printout mounted onto foam core board, from 1/8 in. to 3/16 in., or from 3 to 5 mm.
Product packages tend to be good targets, since they are manufactured from cardboard or other thick materials. Magazine pages lay flat and can work well, but daily newspaper is printed on thinner paper and must be carefully tested before being used.
Printouts from modern laser printers can be very glossy. Under ambient lighting conditions, the glossy surface is not a problem. However, under certain angles, light sources (a lamp, window, or sun, for example) can create a glossy reflection that covers up potentially large parts of the original texture of the printout. A glossy reflection can create tracking and detection issues, similar to partially occluding the target. See the following image as an example of a glossy reflection that can cause problems.
Multi Target Considerations
Since Multi Targets are spatially combined Image Targets, they must fulfill the physical properties of Image Targets. In addition, it is important to guarantee that the shape of the Multi-Target remains intact. Thicker paper and sharp edges on the fold are recommended; sides should not bulge.