How to Characterize the Effects of Windshield Glass

Industry demands and customer expectations for visual quality and performance have increased in accordance with the widespread use of head-up display (HUD) systems in automobiles. HUD systems have come a long way in visual UI and sophistication, from their origin in World War II aircraft to the first automotive HUD from General Motors in 1988.

More than 30 manufacturers of automobiles around the globe now offer HUDs as a standard feature or option. HUDs can be found in a range of luxury vehicles such as Mercedes-Benz, BMW, Rolls-Royce and Jaguar, along with many SUV and mid-range models from companies such as Volvo, Hyundai, Mazda, Genesis, Chevrolet, Audi and Toyota.

The first commercial automotive HUD was in the 1988 Oldsmobile Cutlass Supreme.

The first commercial automotive HUD was in the 1988 Oldsmobile Cutlass Supreme. (Image: © General Motors)

HUD Systems: The Role of the Windshield

Most after-market HUD systems available today – as well as some of the early HUD systems – work by incorporating their own small screen separate from the windshield, into which information projections can be displayed.

Systems that operate in this manner are called combiner HUDs. Other HUD systems operate by projecting “static” images, like navigation data or speed, onto a limited section of the windshield. In both cases, the windshield does not play a significant role, so it does not have significant effects on the visual appearance of the HUD projection.

A typical 2D HUD projection (left) displays information without reference to the external environment; the HUDWAY Drive after-market HUD system (right) with its own display panel.

A typical 2D HUD projection (left) displays information without reference to the external environment; the HUDWAY Drive after-market HUD system (right) with its own display panel. (Right Image © HUDWAY)

HUDs of the future will, by comparison, rely on advanced augmented reality (AR) technology. AR systems such as these will utilize sensors and cameras to project 3D images that appear as though integrated with the environment outside the vehicle. This may be shown by, for example, placing navigational arrows so they present to the driver as though they appear in the correct traffic lane.

AR HUDs such as this will need to use a significant area of the car’s windshield as their display canvas.

This logically means that the surface of the windshield will have a significant impact on the visual quality of the HUD projection as a result. Defects like distortion, ghosting, or magnification of the virtual image can all result from the structure or coatings of the windshield itself.

Automotive HUD systems can present drivers with key information such as speed and navigation data, the location of other vehicles and objects, and lane guides, without requiring them to take their eyes off the road. Shown here is an AR-style HUD where 3D projected images are integrated with the environment outside the vehicle

Automotive HUD systems can present drivers with key information such as speed and navigation data, the location of other vehicles and objects, and lane guides, without requiring them to take their eyes off the road. Shown here is an AR-style HUD where 3D projected images are integrated with the environment outside the vehicle. Image Credit: Radiant Vision Systems

Automakers are already setting strict quality parameters for their windshield manufacturers. Traditional inspection equipment like machine vision cameras and software cannot meet the demand as visual inspection requirements become more complex. Both now and into the future, manufacturers need more powerful inspection tools to ensure they can continue to deliver HUD quality.

Windshield HUD Systems: Measurement Criteria

Typically, windshield testing uses imaging systems for visual inspection and, setting it apart from the qualities of the HUD projection system, isolates the properties of the windshield glass.

Automotive glass manufacturers are provided with vital information about the glass form, layer properties, and wedge angle characteristics through this process of windshield testing and inspection, allowing manufacturers to modify their process and tackle any issues in production and quality control. 

Examples of ghosting (left) and distortion (right), two types of defects commonly introduced by the windshield in HUD displays, which must be corrected to ensure both regulatory compliance and safe vehicle operation

Examples of ghosting (left) and distortion (right), two types of defects commonly introduced by the windshield in HUD displays, which must be corrected to ensure both regulatory compliance and safe vehicle operation. Image Credit: Radiant Vision Systems

As exemplified by Radiant’s ProMetric® Y-series Imaging Colorimeter or I-series Imaging Colorimeter, an effective method to test windshield HUDs is to use an imaging system. A test pattern (such as a dot grid) is projected onto a windshield, and the imager measures the projection to identify and quantify defects when used with the TT-HUD™ module of Radiant’s TrueTest™ Software.

To ensure compliance with both OEM specifications and industry requirements, such as those specified by the Society of Automotive Engineers (SAE J1757-2), multiple image qualities can be evaluated simultaneously.

Radiant’s HUD testing solution compares a test image (first row) to the projected image from a HUD (second row) to identify defects such as distortion and ghosting. Multiple image qualities are evaluated in a single image, providing fast, effective HUD quality inspection

Radiant’s HUD testing solution compares a test image (first row) to the projected image from a HUD (second row) to identify defects such as distortion and ghosting. Multiple image qualities are evaluated in a single image, providing fast, effective HUD quality inspection. Image Credit: Radiant Vision Systems

 

To learn more, read an interview with Radiant Vision Systems Automotive Business Leader, Matt Scholz, via AZoOpics: “Head-Up Displays: System Benefits from 2D to AR.

This information has been sourced, reviewed and adapted from materials provided by Radiant Vision Systems.

For more information on this source, please visit Radiant Vision Systems.

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