Why do my phone's night-sky photos vary from shot to shot with the same manual settings?
Asked 1/18/2016
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2 answers
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I tried photographing Orion with my phone in manual mode to make a time-lapse. I used the same settings for each shot (ISO 1600, 1 second shutter) and took a series at 1-second intervals. Even though the conditions seemed unchanged, the images were not consistent: in the first frame I could see two bright stars in Orion, but in later frames they were much weaker or missing. Why can star photos vary so much between shots when the settings stay the same? Is it related to the phone sensor or image processing?
Originally by user48058. Source · Licensed CC BY-SA 4.0
user48058
10y ago
2 Answers
1
Stars are point sources of light. This makes it especially difficult for a Bayer masked sensor to generate consistent results as the sky moves slightly between each exposure. The raw data obtained on a Bayer masked sensor must be interpolated by comparing and averaging the amount of light striking adjacent pixels as well as nearby pixels sensitive to the same color. But when a point source of light, such as that from a distant star, strikes the sensor it may fall on only one or two pixel wells. The demosaicing algorithms used by many camera makers will often see these extremely small and isolated light sources as shot noise and remove them in an attempt to denoise the image.
Originally by user15871. Source · Licensed CC BY-SA 4.0
user15871
10y ago
0
Generated from our catalog & community — verify before relying on it.
Yes—this can happen even with identical settings, and it usually isn’t because the sensor is changing between shots.
Two main reasons were mentioned:
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Stars are tiny point sources. On a phone sensor, a star may land on only one or two pixels. Most phone cameras use a Bayer color filter and then demosaic/denoise the image. Very small isolated bright pixels can be mistaken for noise and reduced or removed, so a star may appear in one frame and not the next as it shifts slightly across pixels.
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Atmospheric “twinkling”. Turbulence in the air changes how starlight is refracted from moment to moment, making stars brighten, dim, or briefly disappear.
Because of this, star shots can vary noticeably frame to frame even under the same exposure settings. To improve consistency, use longer exposures if possible, or combine multiple shorter frames (stacking/averaging) rather than relying on single images from a phone.
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AI10y ago
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