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Examining advanced graphics in automotive instrument clusters

02 Oct 2012  | Michael Staudenmaier

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Center add-on display: An "Add-on display" is the most common use-case that is currently becoming standard even in low-end cars. The cluster display still has the mechanical needles but features an additional display that is usually located in the center between the gauges. Entry level uses ~4 inch QVGA or WQVGA displays.

The display is used to present additional information like current fuel consumption, temperature or similar nice to have info. Optionally information from the infotainment system is presented here.

In upper-mid to high-end cars larger add-on displays are common. This allows the display to be used for camera images like e.g. night vision, rear-view camera or even a bird-view park-assist image.

Due to the electromechanical instruments the partitioning of the cluster is fixed and cannot be adapted to the situation.

Two displays with central gauge: A compromise still based on a traditional electromechanical needle but offering extended graphical capabilities is a cluster with two displays on both sides of a central mechanical gauge.

It offers significantly more flexibility in displaying information but still has the fixed setup with a fixed electromechanical needle. Screen resolutions common for this use-case are up to SVGA per display.

Fully configurable cluster: For fully configurable clusters large displays with resolution of up to 1280x480 pixels are used today with even higher resolutions planned in future. Those displays are still a significant cost factor which currently limits its application to high-end cars. As there is no mechanical needle available current implementations spend quite some effort to render photorealistic analog needles.

Figure 1: Jaguar (2011) instrument cluster.

Since the cluster content is fully software defined it can be flexibly adapted to the situation. This allows efficient integration of additional situation-dependent information like night vision into the cluster by resizing or moving content that is not that relevant in the current situation.

Head-up display: Head-up displays are projecting the graphic information on the windscreen. The fundamental advantage of those displays is that the information is presented in the normal field of view of the driver looking onto the street. Usually the head-up display is projected in a way that the virtual distance of the graphic is several meters in front of the car which doesn't even require refocusing the eyes when changing from the world outside to the head-up display information.

While head-up displays used to have a rather low resolution and limited color depth, if not even monochrome, this changed fundamentally in the recent past. Meanwhile even for head-up displays rather complex graphic content and a resolution up to WVGA at true color resolution is required.

The content of head-up displays has to be pre-warped to compensate the distortion introduced by the curved windscreen. Today pre-warping is in most cases implemented using a curved mirror which compensates the distortion introduced by the windscreen.

A cost efficient and more flexible solution is electronic warping. There the pre-warping is done on the graphic data using the graphic accelerator or dedicated hardware. Electronic dewarping introduces the flexibility to change the de-warping function on the fly. This enables e.g. to adapt the position of the head-up display depending on the size and position of the driver.

Head-up displays are usually used in combination with a TFT display in the instrument cluster.

Figure 2: BMW 5 Series head-up dsplay.

The use-cases are very different depending on their complexity. This is caused by several factors.

Screen size: the big variation of screen size leads to a significant difference in the number of pixels that have to be generated. In solutions currently in development or on the market 75kPixel up to more than 1MPixels have to be handled for a frame.

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