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#1
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Why not hold sensor sensivity constant?
Is this a legacy issue or is there more to it?
Thanks, Ron |
#2
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Why not hold sensor sensivity constant?
In article .com,
" writes Is this a legacy issue or is there more to it? I don't understand the question. Sensitivity should be set to enable you to obtain the desired depth of field and motion freezing (or blurring) required without needlessly compromising noise. Although I can think of one photographer who would have loved to have the worst noise you can get on a P&S in poor light instead of playing with film and chemicals a couple of decades back. -- Ian G8ILZ |
#3
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Why not hold sensor sensivity constant?
wrote in message oups.com... Is this a legacy issue or is there more to it? I assume you are talking about the ISO setting. Cranking up the ISO means cranking up the gain between the sensor outputs and the A/D converter inputs which is very handy in low-light situations (and others). It comes at the cost of more noise but is still a very worthwhile feature. On some digital cameras, the increase in noise is modest. |
#4
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Why not hold sensor sensivity constant?
In message .com,
" wrote: Is this a legacy issue or is there more to it? It is probably either practically impossible or extremely expensive to make an analog-to-digital conversion that can cover the full dynamic range of the sensor, so different ISOs are available to use different subsets of the sensor's dynamic range. 12 bits is what most cameras digitize to, and that is totally inadequate for low-light shots when the 4096 values are used to represent the full dynamic range of the sensor. A shot taken 4 stops under-exposed at ISO 100 looks like garbage compared to the same shot taken at ISO 1600, with only 1/16 the dynamic range of the sensor amplified for the digitization. It would require very high quality 16-bit digitization to be able to get the same quality at ISO 100 as you get with 12-bit ISO 1600. -- John P Sheehy |
#5
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Why not hold sensor sensivity constant?
I get it. Thanks. It's like selecting a cam in a car appropriate for
you driving style. If only we could all afford twelve valves per cylinder. |
#6
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Why not hold sensor sensivity constant?
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#8
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Why not hold sensor sensivity constant?
" wrote:
I get it. Thanks. It's like selecting a cam in a car appropriate for you driving style. If only we could all afford twelve valves per cylinder. Your analogy is very good. Unfortunately the article you replied to was not correct as regards to dynamic range. But a cam doesn't change the dynamic range... it just puts the precision at different points in that range, which is exactly what ISO adjustments do. -- Floyd L. Davidson http://www.apaflo.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
#9
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Why not hold sensor sensivity constant?
Floyd Davidson wrote:
[] In fact most of the sensors in use today have a dynamic range that is very well matched to a 12 bit AD codec. The better sensors are just slightly better, and could benefit from a 14 bit codec, but since 12 codes provide a dynamic range far beyond what is typically available at all other stages (printing or displaying on a monitor), there is little purpose in using a 14 bit codec. Well, not quite. When using a 12-bit linear encoded sensor, gamma-corrected for an 8-bit JPEG file, the steps at the darkest end are due to the 12-bit resolution, and not to the 8-bit JPEG. The step at the darkest end in an 8-bit JPEG is 1/200,000 of full scale. The step at the darkest end of a 12-bit linear encoding is just 1/4095 of full scale. David |
#10
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Why not hold sensor sensivity constant?
"David J Taylor" wrote:
Floyd Davidson wrote: [] In fact most of the sensors in use today have a dynamic range that is very well matched to a 12 bit AD codec. The better sensors are just slightly better, and could benefit from a 14 bit codec, but since 12 codes provide a dynamic range far beyond what is typically available at all other stages (printing or displaying on a monitor), there is little purpose in using a 14 bit codec. Well, not quite. When using a 12-bit linear encoded sensor, As I noted, most RAW formats are not using 12 bit linear, and there is no reason to assume the codec is linear either. gamma-corrected for an 8-bit JPEG file, the steps at the darkest end are due to the 12-bit resolution, and not to the 8-bit JPEG. The step at the That might be true. It might not too. It depends of course on the RAW format from which the JPEG is derived. As I noted in the original article, as well as above, that is not necessarily linear. Regardless, that has *nothing* to do with my paragraph that you quoted above, which discusses the *dynamic range*, not the pecision of the data. darkest end in an 8-bit JPEG is 1/200,000 of full scale. The step at the darkest end of a 12-bit linear encoding is just 1/4095 of full scale. Which can be changed by either using a non-linear codec, or by simply putting an analog amplifier in front of the codec, with 3 dB steps labeled "ISO". All of which was mentioned in the article to which you have replied. -- Floyd L. Davidson http://www.apaflo.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
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