What in-camera factors affect visible noise in low-light flash photos?
Asked 6/19/2012
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When shooting low light with bounced flash, I often raise ISO and open the aperture to keep some ambient light in the frame. Using a Canon 5D Mark III in Aperture Priority, I noticed that some images at roughly the same settings (for example around f/7.1 and ISO 5000) show very little visible noise, while others show much more.
If ISO and aperture are similar, what factors make noise look better or worse in-camera? Does shutter speed affect noise? Does the amount of light in the scene affect how much noise is visible? Are there any other capture-time factors that help reduce noise, aside from post-processing?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
14y ago
2 Answers
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The amount of light "affects" noise because high ISO noise is most obvious in dark areas of the photo (shadows). If you have a photo with plenty of light in it the noise will not "appear". This is one factor, but not the only one.
Longer shutter speeds usually increases a certain form of noise (called salt & pepper noise or spikes) due to photodiode leakage currents.
Also the ISO affects the amount of noise besides the well known rule of "higher ISO = higher noise". Beyond the real (base) values of ISO (100, 200, 400 etc.) the inbetween values are obtained by pushing/pulling digitally the image hence in ISO 125 (and multiples) you'll see more noise (digital push) while in 160 (and multiples) you'll see less noise than the pushed ISO (ie. 160 ISO has less noise than 125 ISO) because it is a digitall pull. Of course this quasi-'noise reduction' is obtained at the cost of dynamic range.
Another thing (related to exposure time) is sensor's temperature. At higher temperatures the image can be noisier and sometimes can appear 'hot pixels', especially in long/bulb exposures and/or in warm zones/seasons.
Originally by user952. Source · Licensed CC BY-SA 4.0
user952
14y ago
0
Generated from our catalog & community — verify before relying on it.
Yes—visible noise depends strongly on exposure, not just the ISO number.
- More light generally means less visible noise. Noise shows up most in dark areas and shadows, so frames with brighter tones or better exposure will look cleaner.
- Shutter speed can matter indirectly because it changes how much ambient light is recorded. A longer exposure can improve signal-to-noise if the scene is static. Very long exposures can also add sensor-related noise such as hot pixels / “salt and pepper” specks.
- ISO still matters, but exposure is key: underexposed images that are lifted later will show more noise than well-exposed ones.
- Some cameras also behave differently at certain ISO steps. On many cameras, full-stop “real” ISO values are cleaner than some intermediate settings, and certain pulled settings can appear slightly cleaner than pushed ones.
So the main capture-time ways to reduce visible noise are: give the sensor more light, avoid underexposure (especially in shadows), use as long a shutter speed as your subject allows, and choose cleaner ISO settings where possible.
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