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Really cool article. I'm left with just one question: Why are the 16-bit RAW values so limited in their dynamic range? Wouldn't sensor manufacturers want to
by 3JPLW 7y ago
Really cool article. I'm left with just one question:
Why are the 16-bit RAW values so limited in their dynamic range? Wouldn't sensor manufacturers want to have their pixels able to return values that range the whole way from 0x0000 to 0xffff?
- fake-name 7y agoVery few (if any) digital cameras have 16-bit ADCs. Most cameras use 12 or 14 bit ADCs, so they only use 2^12 or 2^14 of the available values. Generally, the RAW files aren't actually 16 bit, but rather a packed structure of the native ADC size. In this case, they're using 16-bit intermediate bitmaps. They're not 16 bit from the RAW. ------ Fujifilm actually has a few cameras with a sensor that can be put in 16-bit mode, but IIRC it's not enabled in software.
- buildbot 7y agoEssentially only very high end digital backs from hasselblad/phase one have 16 bit ADCs, but people disagree if it’s even required, the last two bits are basically noise.
- kurthr 7y agoIf the noise is actually white, that may not be a bad thing for filtering.
- kartickv 7y agoHow is that?
- kortex 7y agoAdditive white gaussian noise is quite well studied and pretty easy to remove with processing. So even if those last few bits are "just noise", if that noise is well-behaved, on the whole image you still have more information. There's also the effect of pixel well depth. I forget the exact interplay, but I believe this usually ends up being the limiting factor before ADC resolution.
- kartickv 7y agoThanks. Regarding pixel well depth, I suppose we can have a sensor with greater pixel size and low pixel count, like a 3840 x 2160 sensor in a full-frame camcorder. Since this would be sold as a video-oriented camera, lack of higher resolution will be a problem problem than in a still-oriented camera.
- fake-name 7y agoYou can remove white noise with oversampling, but you can't usually oversample unless you're shooting a still-life scene and can take multiple exposures. Otherwise, you can't strongly delineate between actual scene artifacts and noise.
- sjwright 7y agoAnd if you oversample multiple exposures, you get more “bits” through the averaging process—if the quantization noise is overwhelmed by random noise.
- tigershark 7y agoI don’t really think that it’s white noise, it’s mostly thermal noise and “reading the sensor” noise (forgot the real name) that have very different shape from white noise. If they were so easily filtered we’d have far superior denoise effectiveness during raw processing.
- dr_zoidberg 7y ago> “reading the sensor” noise "dark current"?
- deleted 7y ago[deleted]
- pletnes 7y agoScientific cameras with 16 bit ADCs will usually, in my limited experience, have active cooling, eg a peltier element and some fans. Otherwise, 12 bit is probably enough.
- mycall 7y agoDalsa has 16-bit too
- 3JPLW 7y agoOh of course, thank you. I even knew that my camera has a 12 bit DAC, but somehow the way it was presented as 16 bit "literal" values made me forget that fact.
- CarVac 7y agoNot really. You want to store the negative values from noise to prevent bias when denoising. And even at base ISO, noise is well above the 14-bit LSB quantization level.