Why does the Canon 450D record 14-bit RAW instead of a higher bit depth?
Asked 12/26/2015
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The Canon 450D’s RAW files are listed as 14-bit. Since RAW data is stored in a container format and could theoretically use larger integer sizes, why doesn’t the camera use something much higher, like 16-bit, 24-bit, or even 64-bit, to capture more tonal values or dynamic range? I’m not asking whether the difference would be visible, but whether a higher bit depth could capture a much wider brightness range or more highlight/shadow detail. Is the 14-bit limit due to file format, buffer size, or the sensor itself?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
10y ago
2 Answers
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The 14 bit depth is the limit of the physical sensors capabilities, it isn't just that the engineers decided to throw away useful data.
An increasing number of bits available in a sensor reflects an increasingly larger complexity of circuitry and precision needed to resolve those progressively finer and finer details. Complexity and precision don't come for free.
While a 64 bit ADC could be hooked up to today's imaging sensors, the bottom 50 bits would be just noise, which is of no use to anyone. Attempts to improve the Signal to noise ratio would dramatically increase the cost of the sensors, plus getting 64 bits of useful data is likely not even possible with today's semiconductor capabilities. If you had a military-scale budget, you may be able to achieve 24 bits, but even that would be pushing it.
Originally by user7977. Source · Licensed CC BY-SA 4.0
user7977
10y ago
0
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The 14-bit limit is mainly set by the sensor and its analog-to-digital conversion, not by the RAW container format.
A camera sensor is an analog device with a finite signal-to-noise ratio. The ADC measures each photosite and assigns it a digital value. If you increase bit depth far beyond the sensor’s real precision, you do not gain meaningful image data — you mostly just record finer steps of noise.
So using 16, 24, or 64 bits would not magically create more dynamic range. More bits only help if the sensor can actually deliver that much clean, distinguishable information. On cameras like the 450D, 14 bits is already around the useful precision the hardware can provide.
In other words:
- higher bit depth does not automatically mean higher dynamic range
- the practical limit is sensor accuracy and noise
- extra bits beyond that would mostly store meaningless noise and make files larger
So the camera isn’t “throwing away” lots of useful data; 14-bit RAW is about the realistic amount of information the sensor can produce.
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