[HN Gopher] SoDaCam: Software-Defined Cameras via Single-Photon ...
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       SoDaCam: Software-Defined Cameras via Single-Photon Imaging
        
       Author : PaulHoule
       Score  : 41 points
       Date   : 2023-09-10 14:58 UTC (8 hours ago)
        
 (HTM) web link (arxiv.org)
 (TXT) w3m dump (arxiv.org)
        
       | rgovostes wrote:
       | Better page: https://wisionlab.com/project/sodacam/
        
         | ooterness wrote:
         | This project is amazing. There's a video about halfway down the
         | project that gives a good summary.
         | 
         | They demo dynamic adjustment of frame rate, i.e., by choosing
         | the time internal for summation of each output pixel. But for
         | me, the really interesting part is when they start summation
         | over more complex trajectories. For example, they know a
         | falling object in the video has a certain initial velocity and
         | acceleration, so they can completely remove motion blur.
         | 
         | It would not surprise me if next-gen ultra-high-speed cameras
         | start using this tech.
        
       | wcerfgba wrote:
       | My understanding is, CCDs accumulate charge in response to
       | photons, whereas these diodes don't, is that correct?
       | 
       | If so, what are the current limits of these diodes which stop us
       | from manufacturing cameras with these diode arrays instead of
       | CCDs?
        
         | DoctorOetker wrote:
         | What is your real question?
         | 
         | CCD is a technology, a strategy or approach to a specific
         | problem if you wish.
         | 
         | diodes are semiconductors, with a positive and negatively doped
         | region (optionally an intrinsic region in between).
         | 
         | A CCD also relies on a diode semiconductor bandgap to liberate
         | charge carriers when a photon exceeding the bandgap energy
         | strikes.
         | 
         | What is your actual question?
         | 
         | Is it "Why don't we use SPAD's in our cell phones and web
         | cams?" ? Thats like "I don't know what it is, but I want it
         | too".
         | 
         | You can't use these in brightly lit scenes, the lighting needs
         | to dim enough in order to register electrical pulses due to
         | individual photons. Instead of a single electron-hole pair,
         | SPAD's are reverse biased beyond "breakdown voltage" such that
         | the released charge carrier will in turn release others (the
         | "A"valanche in SPAD). The breakdown voltage and reverse bias
         | (together with a dark current) means the sensor will heat up.
         | So it would need significant cooling and energy consumption
         | (higher currents per photon at higher breakdown voltage) at
         | normal daytime light intensities. The sheer rate of photons
         | would not allow individual photon pulses to be discriminated as
         | their pulses would overlap... The reason it's not in your phone
         | is because it would be expensive, power hungry (decreasing
         | battery life) and require cooling.
        
           | mnode wrote:
           | This explanation isn't consistent with my understanding. The
           | key reasons are that SPADs have lower quantum efficiency than
           | conventional CCDs and typical SPAD arrays have fewer pixels.
           | Both are improving, but still not competitive for most use
           | cases. Heating is an issue for data transfer, but as the
           | video shows this can be addressed by on-chip processing.
        
           | Y_Y wrote:
           | What is this answer? I'm very familiar with the devices in
           | question but I can't understand why you gave this response.
           | 
           | CCDs count photons (in large numbers), SPADs work hard to
           | register single photons. You can make a camera based on
           | either one, depending on your requirements.
        
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