BIT DEPTH & MEASURING DYNAMIC RANGE
Even if one's digital camera could capture a vast dynamic range, the precision at which light measurements are translated into digital values may limit usable dynamic range. The workhorse which translates these continuous measurements into discrete numerical values is called the analog to digital (A/D) converter. The accuracy of an A/D converter can be described in terms of bits of precision, similar to bit depth in digital images, although care should be taken that these concepts are not used interchangeably. The A/D converter is what creates values for the digital camera's RAW file format.
Bit Precision
of Analog/Digital Converter Contrast Ratio Dynamic Range
f-stops Density
8 256:1 8 2.4
10 1024:1 10 3.0
12 4096:1 12 3.6
14 16384:1 14 4.2
16 65536:1 16 4.8
Note: Above values are for A/D converter precision only, and should not be used to interpret results for 8 and 16-bit image files. Furthermore, values shown are a theoretical maximum, assuming noise is not limiting, and this applies only to linear A/D converters.
As an example, 10-bits of tonal precision translates into a possible brightness range of 0-1023 (since 210 = 1024 levels). Assuming that each A/D converter number is proportional to actual image brightness (meaning twice the pixel value represents twice the brightness), 10-bits of precision can only encode a contrast ratio of 1024:1.
Most digital cameras use a 10 to 14-bit A/D converter, and so their theoretical maximum dynamic range is 10-14 stops. However, this high bit depth only helps minimize image posterization since total dynamic range is usually limited by noise levels. Similar to how a high bit depth image does not necessarily mean that image contains more colors, if a digital camera has a high precision A/D converter it does not necessarily mean it can record a greater dynamic range. In effect, dynamic range can be thought of as the height of a staircase whereas bit depth can be thought of as the number of steps. In practice, the dynamic range of a digital camera does not even approach the A/D converter's theoretical maximum; 8-12 stops is generally all one can expect from the camera.
Even if one's digital camera could capture a vast dynamic range, the precision at which light measurements are translated into digital values may limit usable dynamic range. The workhorse which translates these continuous measurements into discrete numerical values is called the analog to digital (A/D) converter. The accuracy of an A/D converter can be described in terms of bits of precision, similar to bit depth in digital images, although care should be taken that these concepts are not used interchangeably. The A/D converter is what creates values for the digital camera's RAW file format.
Bit Precision
of Analog/Digital Converter Contrast Ratio Dynamic Range
f-stops Density
8 256:1 8 2.4
10 1024:1 10 3.0
12 4096:1 12 3.6
14 16384:1 14 4.2
16 65536:1 16 4.8
Note: Above values are for A/D converter precision only, and should not be used to interpret results for 8 and 16-bit image files. Furthermore, values shown are a theoretical maximum, assuming noise is not limiting, and this applies only to linear A/D converters.
As an example, 10-bits of tonal precision translates into a possible brightness range of 0-1023 (since 210 = 1024 levels). Assuming that each A/D converter number is proportional to actual image brightness (meaning twice the pixel value represents twice the brightness), 10-bits of precision can only encode a contrast ratio of 1024:1.
Most digital cameras use a 10 to 14-bit A/D converter, and so their theoretical maximum dynamic range is 10-14 stops. However, this high bit depth only helps minimize image posterization since total dynamic range is usually limited by noise levels. Similar to how a high bit depth image does not necessarily mean that image contains more colors, if a digital camera has a high precision A/D converter it does not necessarily mean it can record a greater dynamic range. In effect, dynamic range can be thought of as the height of a staircase whereas bit depth can be thought of as the number of steps. In practice, the dynamic range of a digital camera does not even approach the A/D converter's theoretical maximum; 8-12 stops is generally all one can expect from the camera.
This is what's had me confused on this forum. All definitions I see of ADCs say they have a fixed "theoritical" tonal DR value. But I keep being told that's not the case. Because the Sony sensor's DR is greater than the ADC's theoritical DR, it does not exhibit noise in shadow recovery....to get back to my definition:
The Sony's sensor DR is able to fill full theoretical 14bit space at base ISO....16384:1. The Canon's sensor DR isn't able to fill that.
Just an idea for the lay crowd.... And why this board is still stuck on SNR flames
You're welcome POTN!!!
