With naive point-based rendering, stars in the centre of the screen will be too bright (left). To correct this, the projected size of the stars has to be incorporated in the luminance computation (centre). For perspectively correct glaring, the glare must not be computed in screen space, because else the stars will look flat in immersive scenarios (right, observe the now correct ellipsoidal glare around bright stars). For these images, 50 million stars from the Gaia catalogue were rendered by our proposed software rasterizer. About 22 million sars were inside the frustum. Rendering the right view took about 8 ms at 4K resolution on an RTX 4070 Super.
Abstract
Many applications need to display realistic stars. However, rendering stars with their correct luminance is surprisingly difficult: Usually, stars are so far away from the observer, that they appear smaller than a single pixel. As one can not visualize objects smaller than a pixel, one has to either distribute a star’s luminance over an entire pixel or draw some kind of proxy geometry for the star. We also have to consider that pixels at the edge of the screen cover a smaller portion of the observer’s field of view than pixels in the centre. Hence, single-pixel stars at the edge of the screen have to be drawn proportionally brighter than those in the centre. This is especially important for virtual-reality or dome renderings, where the field of view is large. In this paper, we compare different rendering techniques for stars and show how to compute their luminance based on the solid angle covered by their geometric proxies. This includes point-based stars, and various types of camera-aligned billboards. In addition, we present a software rasterizer which outperforms these classic rendering techniques in almost all cases. Furthermore, we show how a perception-based glare filter can be used to efficiently distribute a star's luminance to neighbouring pixels. Our implementation is part of the open-source space-visualization software CosmoScout VR.
Publication
Schneegans, S., Kreskowski, A., Gerndt, A.
Smaller than Pixels: Rendering Millions of Stars in Real-Time
To be presented at the 2025 Eurographics conference (Short-Paper Track), London, England.
[preprint, video, code on GitHub]