All That Noise!

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flyinglentris Contributing Member • Posts: 748
All That Noise!

It's quite amazing the numerous vistas of technical exploration and research that digital photography offers. Most recently, I was digging into some topics regarding Astronomy Photography and came across some interesting glints on noise.

Folks doing Astronomy Photography indulge in some noise control practices that the average photographer would find to say the least, peculiar. For example, it is not likely that the average photographer would try to calibrate their camera noise by taking dark frames, biased frames or flat frames. Nor would the average photographer even know what these techniques entail. Some might not even understand what every camera owes to noise, dark noise, read noise and ambient noise. There's that word 'dark' again. May the force be with us all and the dark side shall not rule the galaxy.

Dark noise is generated by every camera sensor during camera exposure time. It is a thermal generated noise resulting from sensor activity during photo-electric capture of photons. The longer the exposure the more thermal noise. Burst shots? Similar.

Read noise is generated during the Analog to Digital Conversion (and amplification or gain) of the photosites analog charge to digital form for recording in camera memory. It is also thermal in nature and is always present.

Ambient noise is not generated by the camera sensor and is not thermal in nature. It originates from lighting conditions, light pollution, haze, lens flare and aberrations, vignetting and other external sources of image degradation.

The percentage of noise induced charge potential relative to the actual photo-site photon charge collected is the Signal to Noise Ratio (SNR). This is what we all want to improve.

Camera vendors generally compensate inherent sensor noise levels and provide firmware solutions for ISO (gain/amplification) noise reduction. We all generally know and accept that.

For those who attach their cameras to telescopes, enter the dark frame, the biased frame and the flat frame. Deep space photography requires particular attention to eliminating noise and so Astronomy Photographers pay a much keener attention to noise levels than do we who shoot more earth-bound images. Astro-photographers take extra images to calibrate noise.

I'm only scratching the Astronomy Photography surface myself, so forgive any clues of ignorance.

Dark Frames are taken by actually covering the end of the telescope or capping the camera and taking a dark image that will be used to adjust for noise.

Bias Frames are taken with zero exposure time and record noise characteristics of the specific camera to adjust for noise.

Flat Frames are taken using the exposure setup intended for a shot and are used to achieve an even field illumination and eliminate vignetting. Multiple flat frame shots may be required to properly calibrate.

And to top all that off, Astronomy Photographers can choose to use specialty cameras specifically purposed for Astronomy Photography. These cameras incorporate cooled sensors to ameliorate sensor thermal noise. For you Canon shooters who have seen the introduction of Canon's new EOS Ra camera, you might well wonder if it incorporates a cooled sensor and whether that might be valuable for non-Astronomy Photography.

Just thought I'd share as this perspective of Astronomy Photographers on camera noise is somewhat different that what others might be familiar with.

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"If you are among those who believe that it has all been done already and nothing new can be achieved, you've murdered your own artistry before ever letting it live. You abort it in its fetal state. There is much that has yet to be spoken in art and composition and it grows with the passage of time. Evolving technologies, world environments and ideologies all drive change in thoughts, passion and expression. There is no way that it can all ever be done already. And therein lies the venue for the creative artist, a venue that is as diverse as the universe is unmapped and unexplored." - Quote from FlyingLentris
flyinglentris in LLOMA

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